How well understood are the long-term effects of nuclear radiation?

How well understood are the long-term effects of nuclear radiation?

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Sometimes, when people are concerned about radiation, it is not because it is precisely quantified how dangerous it is, but because we don't know how dangerous it is.

How well understood are the long-term effects of nuclear radiation, for example on cancer? (As opposed to short-term effects such as acute radiation sickness, which is easy to quantify)

I assume this can be researched from an epidemiological approach (Wikipedia mentions an epidemiological study on the atomic bombing of Hiroshima and Nagasaki, for example), and also from an experimental approach.

Also, is the effects of radiation easy to understand, or difficult? My assumption is that something physical, like radioactivity, would be easier to understand than the effects of more complicated things, like complicated organic chemicals or obesity.

The three major nuclear incidents I can think of are the Japanese atomic bomb attacks, the Chernobyl disaster, and Fukushima disaster. Of course other nuclear incidents have occurred, but usually give much higher doses to far fewer people.

Many studies have been done on the survivors from the atomic bomb attacks, and increased rates of cancer have been the strongest conclusion. This review article looks at those studies for both cancer and non-cancer effects. Leukemia is the most well known cancer to be caused by radiation, and excess leukemia was discovered in bomb survivors within 5 years of the attacks. Rates of most solid tumors had increased by 10 years after the attacks. However "Even 55 years after the bombings over 40% of the Life Span Study cohort remain alive", indicating that the amount of radiation most people were exposed to wasn't enough to kill them. Here is another article on atomic bomb survivors.

The Chernobyl accident was a very different type of exposure, but many people were exposed to radioactive materials. Immediately after the disaster, the "liquidators" received high doses of radiation while cleaning up the site and building the containment structures, but very few have died from radiation exposure. While the environment around the power plant did suffer in the years after the accident, after the humans moved away the environment has greatly improved. Thyroid cancer rates increased due to Iodine-131 exposure, especially among those exposed as children, but rates were still low. Yellow = adults Blue = Adolescents Red = Children.

It is too soon to draw many conclusions about the Fukushima accident, but some studies (7, 8) have tried to predict the number of cancer cases that will be caused by it. In general the rates are expected to be low, with far fewer deaths than were caused by the earthquake and tsunami that caused the accident.

A few instances exposed small numbers of people to very high doses, and are interesting from a radiation safety veiwpoint. The infamous "Demon Core" killed 2 scientists in separate accidents while handling the core. The Goiania incident involved men breaking into an old hospital and stealing a radiation source without realizing what it was. They broke the source open and passed the radioactive material around because it looked cool, resulting in several deaths due to acute radiation sickness.

While radiation can be dangerous, with proper precautions we can avoid accidents and disasters. Remember that Chernobyl was a poorly designed Soviet reactor, and that Fukushima was a 50 year old plant that needed both a magnitude 9 earthquake and a 30 foot wave to disable it. Modern nuclear plants can be built safely and provide clean electricity for many decades, and if they are breeder reactors can recycle the used fuel to reduce both the amount and half-life of the material, making storage easier.

General overview of the effects of nuclear testing

The material contained in this chapter is based on official government sources as well as information provided by research institutions, policy organizations, peer-reviewed journals and eye witness accounts.

The CTBTO remains neutral in any ongoing disputes related to compensation for veterans of the nuclear test programmes.

Nuclear weapons have been tested in all environments since 1945: in the atmosphere, underground and underwater. Tests have been carried out onboard barges, on top of towers, suspended from balloons, on the Earth’s surface, more than 600 metres underwater and over 200 metres underground. Nuclear test bombs have also been dropped by aircraft and fired by rockets up to 320 km into the atmosphere.

Frigate Bird nuclear test explosion seen through the periscope of the submarine USS Carbonero (SS-337), Johnston Atoll, Central Pacific Ocean, 1962.

The first nuclear test was carried out by the United States in July 1945, followed by the Soviet Union in 1949, the United Kingdom in 1952, France in 1960, and China in 1964. The National Resources Defense Council estimated the total yield of all nuclear tests conducted between 1945 and 1980 at 510 megatons (Mt). Atmospheric tests alone accounted for 428 mt, equivalent to over 29,000 Hiroshima size bombs.

The amount of radioactivity generated by a nuclear explosion can vary considerably depending upon a number of factors. These include the size of the weapon and the location of the burst. An explosion at ground level may be expected to generate more dust and other radioactive particulate matters than an air burst. The dispersion of radioactive material is also dependent upon weather conditions.

Carbon Dioxide

Nuclear power has been called a clean source of energy because the power plants do not release carbon dioxide. While this is true, it is deceiving. Nuclear power plants may not emit carbon dioxide during operation, but high amounts of carbon dioxide are emitted in activities related to building and running the plants. Nuclear power plants use uranium as fuel. The process of mining uranium releases high amounts of carbon dioxide into the environment. Carbon dioxide is also released into the environment when new nuclear power plants are built. Finally, the transport of radioactive waste also causes carbon dioxide emissions.

How well understood are the long-term effects of nuclear radiation? - Biology


A mobile phone is a phone that can make and receive telephone calls over a radio link while moving around a wide geographic area. It does so by connecting to a cellular network provided by amobile phone operator, allowing access to the public telephone network. By contrast, a cordless telephone is used only within the short range of a single, private base station.The first hand-held cell phone was demonstrated by John F. Mitchelland Martin Cooper of Motorola in 1973, using a handset weighing around 4.4 pounds (2 kg).In 1983, the DynaTAC 8000x was the first to be commercially available. From 1983 to 2014, worldwide mobile phone subscriptions grew from zero to over 7 billion, penetrating 100% of the global population and reaching the bottom of the economic pyramid. In 2014, the top cell phone manufacturers were Samsung, Nokia, Apple, and LG.

Early cell phones were just for talking. Gradually, features like voicemail were added, but the main purpose was talk. Eventually, cell phone manufacturers began to realize that they could integrate other technologies into their phone and expand its features. The earliest smartphones let users access email, and use the phone as a fax machine, pager, and address book.

Just in recent years, cell phone designs have actually started to become larger and simpler, making room for a larger screen and less buttons. Because phones have become mobile media devices, the most desirable aspect is a large, clear, high-definition screen for optimal web viewing. Even the keyboard is being taken away, replaced by a touch screen keyboard that only comes out when you need it

Some Common Features To All Mobile Handsets

The common components found on all phones are:

1. A battery, providing the power source for the phone functions.

2. An input mechanism to allow the user to interact with the phone.

3. The most common input mechanism is a keypad, but touch screens are also found in most smartphones.

4. A screen which echoes the user's typing, displays text messages, contacts and more.

5. Basic mobile phone services to allow users to make calls and send text messages.

6. All GSM phones use a SIM card to allow an account to be swapped among devices. Some CDMA devices also have a similar card called a R-UIM.

7. Individual GSM, WCDMA, iDEN and some satellite phone devices are uniquely identified by an International Mobile Equipment Identity (IMEI) number.

What is a Base Station?

The term base station is used in the context of mobile telephony, wireless computer networking and other wireless communications and in land surveying: in surveying it is a GPS receiver at a known position, while in wireless communications it is a transceiver connecting a number of other devices to one another and/or to a wider area. In mobile telephony it provides the connection between mobile phonesand the wider telephone network.

Health Hazards Of Base Stations

Another area of concern is the radiation emitted by the fixed infrastructure used in mobile telephony, such as base stations and their antennas, which provide the link to and from mobile phones. This is because, in contrast to mobile handsets, it is emitted continuously and is more powerful at close quarters. On the other hand, field intensities drop rapidly with distance away from the base of transmitters because of the attenuation of power with the square of distance.

One popular design of mobile phone antenna is the sector antenna, whose coverage is 120 degrees horizontally and about 𕓃 degrees from the vertical. Because base stations operate at less than 100 watts, the radiation at ground level is much weaker than a cell phone due to the power relationship appropriate for that design of antenna. Base station emissions must comply with safety guidelines. Some countries, however (such as South Africa, for example), have no health regulations governing the placement of base stations.

Mobile Phone Radiation And Health

The effect of mobile phone radiation on human health is a subject of interest and study worldwide, as a result of the increase in mobile phone usage throughout the world. As of November 2011, there were more than 6 billion subscriptions worldwide. Mobile phones use electromagnetic radiation in the microwave range. Other digital wireless systems, such as data communication networks, produce similar radiation.

In 2011, International Agency for Research on Cancer (IARC) classified mobile phone radiation as Group 2B - possibly carcinogenic (not Group 2A - probably carcinogenic - nor the dangerous Group 1). That means that there "could be some risk" of carcinogenicity, so additional research into the long-term, heavy use of mobile phones needs to be conducted. The WHO added in June 2011 that "to date, no adverse health effects have been established as being caused by mobile phone use", a point they reiterated in October 2014. Some national radiation advisory authorities have recommended measures to minimize exposure to their citizens as a precautionary approach.

Some Of The Potential Side Effects Of Exposure To Electromagnetic Radiation

&bull Enzyme Changes That Affect DNA

&bull Increased Risk For Alzheimer&rsquos Disease

&bull Increased Risk For Heart Conditions

&bull Neurological Hormone Changes Linked Impaired Brain Function

Effects Of Mobile Radiation On Living Tissue

Radiation Absorption

Part of the radio waves emitted by a mobile telephone handset are absorbed by the body. The radio waves emitted by a GSM handset are typically below a watt. The maximum power output from a mobile phone is regulated by the mobile phone standard and by the regulatory agencies in each country.

In most systems the cellphone and the base stationcheck reception quality and signal strength and the power level is increased or decreased automatically, within a certain span, to accommodate different situations, such as inside or outside of buildings and vehicles.

The rate at which energy is absorbed by the human body is measured by the Specific Absorption Rate (SAR), and its maximum levels for modern handsets have been set by governmental regulating agencies in many countries.

In the USA, the Federal Communications Commission (FCC) has set a SAR limit of 1.6 W/kg, averaged over a volume of 1 gram of tissue, for the head. In Europe, the limit is 2 W/kg, averaged over a volume of 10 grams of tissue. SAR data for specific mobile phones, along with other useful information, can be found directly on manufacturers' websites, as well as on third party web sites. It is worth noting that thermal radiation is not comparable to ionizing radiation in that it only increases the temperature in normal matter, it does not break molecular bonds or release electrons from their atoms.

Thermal Effects

One well-understood effect of microwave radiation is dielectric heating, in which any dielectric material (such as living tissue) is heated by rotations of polar molecules induced by the electromagnetic field. In the case of a person using a cell phone, most of the heating effect will occur at the surface of the head, causing its temperature to increase by a fraction of a degree. In this case, the level of temperature increase is an order of magnitude less than that obtained during the exposure of the head to direct sunlight. The brain's blood circulation is capable of disposing of excess heat by increasing local blood flow. However, the cornea of the eye does not have this temperature regulation mechanism and exposure of 2&ndash3 hours duration has been reported to produce cataracts in rabbits' eyes at SAR values from 100&ndash140 W/kg, which produced lenticular temperatures of 41 °C. This has known to cause premature cataract in humans.

A image via thermal scans showing heating of the facial skin after 4 hours of phone usage.

*Thermal effects have also known to cause harm to ear drum and impair hearing in the long term.

Blood&ndashBrain Barrier Effects

Swedish researchers from Lund University have studied the effects of mobile radiation on the brain. They found a leakage of albumin into the brain via a permeated blood&ndashbrain barrier. This confirms earlier work on the blood&ndashbrain barrier by Allan Frey, Oscar and Hawkins, and Albert and Kerns.
Prof Leszczynski of Finland's radiation and nuclear safety authority found that, at the maximum legal limit for mobile radiation, one protein in particular, HSP 27, was affected. HSP 27 played a critical role in the integrity of the blood-brain barrier.

Cognitive Effects

A 2009 study, examined the effects of exposure to radiofrequency radiation (RFR) emitted by standard GSM cell phones on the cognitive functions of humans.
The study confirmed longer (slower) response times to a spatial working memory task when exposed to RFR from a standard GSM cellular phone placed next to the head of male subjects, and showed that longer duration of exposure to RFR may increase the effects on performance.
Right-handed subjects exposed to RFR on the left side of their head on average had significantly longer response times when compared to exposure to the right side and sham-exposure.

Electromagnetic Hypersensitivity

Some users of mobile handsets have reported feeling several unspecific symptoms during and after its use ranging from burning and tingling sensations in the skin of the head and extremities, fatigue, sleep disturbances, dizziness, loss of mental attention, reaction times and memory retentiveness, headaches, malaise, tachycardia (heart palpitations), to disturbances of the digestive system. Reports have noted that all of these symptoms can also be attributed to stress and that current research cannot separate the symptoms from nocebo effects.

Genotoxic Effects

In December 2004, a pan-European study named REFLEX (Risk Evaluation of Potential Environmental Hazards from Low Energy Electromagnetic Field (EMF) Exposure Using Sensitive in vitro Methods), involving 12 collaborating laboratories in several countries showed some compelling evidence of DNA damage of cells in in-vitro cultures, when exposed between 0.3 to 2 watts/kg, whole-sample average. There were indications, but not rigorous evidence of other cell changes, including damage to chromosomes, alterations in the activity of certain genes and a boosted rate of cell division.

Australian research conducted in 2009, by subjecting in vitro samples of human spermatozoa to radio-frequency radiation at 1.8 GHz and specific absorption rates (SAR) of 0.4 to 27.5 W/kg showed a correlation between increasing SAR and decreased motility and vitality in sperm, increased oxidative stress and 8-Oxo-2'-deoxyguanosine markers, stimulating DNA base adduct formation and increased DNA fragmentation.

Behavioural Effects

A study shows that exposure to excessive mobile radiation during pregnancy can cause a risk of ADHD in child.

Sperm Count And Sperm Quality

Exposure to SAR values for long times for those men who keep the mobile phones in their lower pockets for most of the time, increases the temperature of groin and the radiation has known to cause considerable lowering of the sperm motility and vitality of sperm.

Tips For Reducing Potential Harmful Effects of Mobile Phone Radiation

1. When on a call, use a wired headset or speakerphone mode. Use a Bluetooth headset, which emits a smaller amount of radiation, only when talking. When not using the headset, keep it off your body.

2. Place the mobile phone away from your body when on a call.

3. Do not carry mobile phones in pockets of pants or in shirts or bras. Use a belt holster designed to shield the body from radiation.

4. Avoid using a mobile phone in a moving car, train, bus, or in rural areas at some distance from a cell tower. Distance from a cell tower will increase the cell phone&rsquos radiation output.

5. Turn the mobile phone off when you don't need to use it.

6. Use a corded landline phone instead of a wireless phone, which also emits radiation.

7. Avoid using mobile phone inside of buildings, particularly those with steel structures, which increases the device's radiation output because signals are not as strong.

8. Do not allow children, whose bodies are more vulnerable to absorbing radiation, to sleep with a cell phone beneath their pillow or keep it at the bedside.

9. Do not allow children under 18 to use a mobile phone except in emergencies.

10. When making a call, do not hold the phone to your ear until after the person on the other line answers. The device emits more radiation before a call goes through.


The conclusion drawn from the investigatory project finally states the mobile radiation is harmful to human health. The effects may not be noted almost immediately, but will be causing adverse effects to the present as well the future generations because of the ability of the radiations to effect and mutate human DNA which have a high potential to cause mutations and new diseases in the future generations. Mobile radiations present a very high risk of brain cancer and tumours in humans and most prominently in children below the age of 5 years.

Precautionary measure should be taken to protect one&rsquos self and family and friends from the harmful effects of mobile radiation. j Mobile radiation might not seem harmful in almost immediate effects but is such a slow poison to cause harmful effects to us and even our future generations, in the long run.

How well understood are the long-term effects of nuclear radiation? - Biology

reprinted with permission from
No Immediate Danger, Prognosis for a Radioactive Earth, by Dr Rosalie Bertell
The Book Publishing Company -- Summertown, Tennessee 38483
ISBN 0-913990-25-2
pages 15-63.

The Problem:
Nuclear Radiation and its Biological Effects

The future of humankind is present today within the bodies of living people, animals and plants -- the whole seedbearing biosphere. This living biosystem which we take so much for granted has evolved slowly into a relatively stable dynamic equilibrium, with predictable interactions between plants and animals, between microscopic and macroscopic life, between environmental pollutants and human health. Changes in the environment disturb this balance in two ways: first, by altering the carefully evolved seed by randomly damaging it, and second, by altering the habitat, i.e. food, climate or environment, to which the seed and/or organism has been adapted, making life for future generations more difficult or even impossible.
Although examples of maladaptation in nature and resulting species extinction abound, our focus here is on human seed, the sperm and ovum, and the effect on it and on the human habitat resulting from increasing ionising radiation in the environment.
The increased use of radioactive materials, which is a direct outgrowth of the current military and energy policies of the developed world, provides an opportunity for gauging what priority these countries give to the health and well-being of individual citizens, and for gauging governments' understanding of the tension between individual and national survival. The first indicator of underlying national priorities is the precision or lack of precision with which health effects are predicted, and the thoroughness with which an audit is taken and the predictions checked against reality. The audit findings should be reported to the person or people affected, and their participation sought in formulating changes in policy to remedy any unanticipated problems. The individual's sense of self-preservation and personal benefit, in such an ideal system, would give realistic feedback to governments on the acceptability of national policy. The combined experiences of governing and governed would forge a national consensus on future directions.

    ABCC Atomic Bomb Casualty Commission. Now called Radiation Effects Research Foundation (RERF)

  • Microcurie: one-millionth of a curie.
    (3.7 x 10^4 disintegrations per second) mCi is the symbol used.
  • Picocurie: one-millionth of a microcurie.
    (3.7 x 10^-2 disintegrations per second) pCi is the symbol used.

  • Natural background radiation --
    emissions from radioactive chemicals which are not man-made. These chemicals include uranium, radon, potassium and other trace elements. They are made more hazardous through human activities such as mining and milling, since this makes them more available for uptake in food, air and water.
  • Background radiation --
    includes emissions from radioactive chemicals which occur naturally and those which result from the nuclear fission process. The meaning of this term is vague. In a licensing process it includes radiation from all sources other than the particular nuclear facility being licensed, even if the source includes a second nuclear facility located on the same site (US regulations). Radioactive chemicals released from a nuclear power plant are called `background' after one year.

The Fissioning Process and its Consequences

In order to understand nuclear technology and its impact on human health, three atomic-level events must be understood: fissioning, activation and ionisation. Fissioning, i.e. the splitting of the uranium or plutonium atom, is responsible for producing radioactive fission fragments and activation products. These in turn cause the ionisation of normal atoms, leading to a chain of microscopic events we may eventually observe as a cancer death or a deformed child.
Radioactive fission products are produced in nuclear reactors. They are variant forms of the ordinary chemicals which are the building blocks of all material and living things. The radioactive forms of these chemicals were, prior to 1943, present in only trace quantities in isolated places in the environment as, for example, in South Africa where it appears that a small nuclear fission reaction occurred spontaneously about 1700 million years ago.
When a uranium atom is split or fissioned, it does not always split in the same place. The two pieces, called fragments, are chemicals of lower atomic weight than uranium. Each fragment receives part of the nucleus and part of the electrons of the original large uranium atom. The uranium atoms, of course, cease to exist after they are split. Instead, more than 80 different possible fission products are formed, each having the chemical properties usually associated with their structure, but having the added capability of releasing ionising radiation. X-rays, alpha particles, beta particles, gamma rays (like X-rays) or neutrons can be released by these `created' chemicals. All these can cause `ionisation', i.e. by knocking an electron out of its normal orbit around the nucleus of an atom they produce two `ions', the negatively charged electron and the rest of the atom which now has a net positive electrical charge.
The atomic structure of fission fragments is unstable. The atom will at some time release the destabilizing particle and return to a natural, low-energy, more stable form. Every such release of energy is an explosion on the microscopic level. With each fissioning, 2 or 3 neutrons are released which can strike a nearby U235 atom causing more fissioning in what is usually called a chain reaction.
The violence of the chain reaction is such that it can also yield what are called activation products, i.e. it can cause already existing chemicals in air, water or other nearby materials to absorb energy, change their structure slightly and become radioactive. As these high-energy forms of natural materials eventually return to their normal stable state, they can also release ionising radiation. About 300 different radioactive chemicals are created with each chain reaction.[1] It takes hundreds of thousands of years for all the newly formed radioactive chemicals to return to a stable state.
In a nuclear power plant the fissioning takes place inside the zirconium or magnesium alloy cladding which encloses the fuel rods. Most of the fission fragments are trapped within the rods. However, the activation products can be formed in the surrounding air, water, pipes and containment building. The nuclear plant itself becomes unusable with time and must eventually be dismantled and isolated as radioactive waste.
After fissioning, the fuel rods are said to be `spent'. They contain the greatest concentration of radioactivity of any material on the planet earth -- many hundreds of thousands of times the concentration in granite or even in uranium mill tailings (waste). The spent fuel rods contain gamma radiation emitters (which are similar to X-ray emitters) so they must not only be isolated from the biosphere, but they must also be shielded with water and thick lead walls. Direct human exposure to spent fuel rods means certain death.
In reprocessing, spent fuel rods are broken open and the outer cladding is dissolved in nitric acid. The plutonium is separated out for use in nuclear weapons or for fuel in a breeder or mixed oxide nuclear reactor. The remaining highly radioactive debris is stored as liquid in large carbon or stainless steel drums, awaiting some kind of solidification and burial in a permanent repository. Waste of lower radioactivity is buried in dirt trenches or -- as in Windscale (Sellafield) in England -- piped out to sea. The spent nuclear fuel rods and liquid reprocessing waste are called `high level radioactive waste'. It must be kept secure for hundreds of thousands of years -- essentially forever. Lower level waste may be equally long-lived, but it is less concentrated.
In above-ground nuclear weapon testing, there is no attempt to contain any of the fission or activation products. Everything is released into the air and on to the land. Some underground tests are also designed to release most of the radioactive particles these are called crater shots or shots with unstemmed holes. Even when below-ground shots are designed to be contained, they normally lose the radioactive gases and some particulates. The radionuclides trapped in the ground can also migrate downwards in the earth to water reservoirs which provide irrigation and drinking water for human purposes, although this process is slow. Radioactive debris piped out to sea can be washed back on shore or can contaminate fish.
In all nuclear reactions, some radioactive material -- namely the chemically inert or so-called `noble' gases, other gases, radioactive carbon, water, iodine, and small particulates of plutonium and other transuranics (i.e. chemicals of higher atomic number than uranium) -- is immediately added to the air, water and land of the biosphere. In the far-distant future, all the long-lived radioactive material, even that now stored and trapped, will mix with the biosphere unless each generation repackages it. Our planet earth is designed to recycle everything.
The radioactive chemicals which escape to the biosphere can combine with one another or with stable chemicals to form molecules which may be soluble or insoluble in water which may be solids, liquids or gases at ordinary temperature and pressure which may be able to enter into biochemical reactions or be biologically inert. The radioactive materials may be external to the body and still give off destructive penetrating radiation. They may also be taken into the body with air, food and water or through an open wound, becoming even more dangerous as they release their energy in close proximity to living cells and delicate body organs. They may remain near the place of entry into the body or travel in the bloodstream or lymph fluid. They can be incorporated into the tissue or bone. They may remain in the body for minutes or hours or a lifetime. In nuclear medicine, for example, radioactive tracer chemicals are deliberately chosen among those quickly excreted by the body. Most of the radioactive particles decay into other radioactive `daughter' products which may have very different physical, chemical and radiological properties from the parent radioactive chemical. The average number of such radioactive daughters of fission products produced before a stable chemical form is reached, is four.
Besides their ability to give off ionising radiation, many of the radioactive particles are biologically toxic for other reasons. Radioactive lead, a daughter product of the radon gas released by uranium mining retains the ability to cause brain damage exercised by non-radioactive lead. Plutonium is biologically and chemically attracted to bone as is the naturally occurring radioactive chemical radium. However, plutonium clumps on the surface of bone, delivering a concentrated dose of alpha radiation to surrounding cells, whereas radium diffuses homogeneously in bone and thus has a lesser localized cell damage effect. This makes plutonium, because of its concentration, much more biologically toxic than a comparable amount of radium. Some allowance for this physiological difference has been made in setting plutonium standards, but there is evidence that there is more than twenty times more damage caused than was suspected at the time of standard setting.[2]
The cellular damage caused by internally deposited radioactive particles becomes manifest as a health effect related to the particular organ damaged. For example, radionuclides lodged in the bones can damage bone marrow and cause bone cancers or leukaemia, while radionuclides lodged in the lungs can cause respiratory diseases. Generalised whole body exposure to radiation can be expressed as a stress related to a person's hereditary medical weakness. Individual breakdown usually occurs at our weakest point. In this way, man-made radiation mimics natural radiation and causes the ageing or breakdown process to be accelerated.

Radioactive Particles and Living Cells: Penetration Power

Radioactive fission products, whether they are biochemically inert or biochemically active, can do biological damage when either outside the body or within.
X-rays and gamma rays are photons, i.e. high-energy light-waves. When emitted by a source, for example, radium or cobalt, located outside the body, they easily pass through the body, hence they are usually called penetrating radiation. The familiar lead apron provided for patients in some medical procedures stops X-rays from reaching reproductive organs. A thick lead barrier or wall is used to protect the X-ray technician. Because X-rays are penetrating, they can be used in diagnostic medicine to image human bones or human organs made opaque by a dye. These internal body parts are differentially penetrable. Where bones absorb the energy, no X-rays hit the sensitive X-ray film, giving a contrast to form the picture of the bones on the radiation-sensitive X-ray plate. High-energy gamma rays, which easily penetrate bone, would be unsuitable for such medical usage because the film would be uniformly exposed. In photography jargon, the picture would be a `white out' with no contrasts. No radiation remains in the body after an X-ray picture is taken. It is like light passing through a window. The damage it may have caused on the way through, however, remains.
Some radioactive substances give off beta particles, or electrons, as they release energy and seek a stable atomic state. These are small negatively charged particles which can penetrate skin but cannot penetrate through the whole body as do X-rays and gamma rays.
Microscopic nuclear explosions of some radioactive chemicals release high-energy alpha particles. An alpha particle, the nucleus of a helium atom, is a positively charged particle. It is larger in size than a beta particle, like a cannon-ball relative to a bullet, having correspondingly less penetrating power but more impact. Alpha particles can be stopped by human skin, but they may damage the skin in the process. Both alpha and beta particles penetrate cell membranes more easily than they penetrate skin. Hence ingesting, inhaling or absorbing radioactive chemicals capable of emitting alpha or beta particles and thereby placing them inside delicate body parts such as the lungs, heart, brain or kidneys, always poses serious threats to human health.[3] Plutonium is an alpha emitter, and no quantity inhaled has been found to be too small to induce lung cancer in animals.
The skin, of course, can stop alpha or beta radiation inside the body tissue from escaping outwards and damaging, for example, a baby one is holding or another person sitting nearby. Also, it is impossible to detect these particles with most whole body `counters' such as are used in hospitals and nuclear installations. These counters can only detect X-rays and gamma rays emitted from within the body.
Splitting a uranium atom also releases neutrons, which act like microscopically small bullets. Neutrons are about one-fourth the size of alpha particles and have almost 2,000 times the mass of an electron. If there are other fissionable atoms nearby (uranium 235 or plutonium 239, for example) these neutron projectiles may strike them, causing them to split and to release more neutrons. This is the familiar chain reaction. It takes place spontaneously when fissionable material is sufficiently concentrated, i.e. forms a critical mass. In a typical atomic bomb the fissioning is very rapid. In a nuclear reactor, water, gas or the control rods function to slow down or to absorb neutrons and control the chain reaction.
Neutrons escaping from the fission reaction can penetrate the human body. They are among the most biologically destructive ot the fission products. They have a short range, however, and in the absence of fissionable material they will quickly be absorbed by non-radioactive materials. Some of these latter become radioactive in the process, as was noted earlier, and are called activation products.

The complexity of setting health standards for exposure to the mixture of radioactive chemicals and ionising particles released in fissioning should be apparent. As a first move towards a reasonable subdivision of the hazard itself, separate standard setting was done for external radiation exposure, i.e. when the radioactive source was outside the body, and internal radiation exposure, i.e. when the radioactive source was inside the body.
Both these categories can then be subdivided into exposures to particular parts of the body or particular internal organs. The biological effect of an X-ray of the pelvic area differs from the biological effect of a dental X-ray, even if the radiation dose to the skin is the same. Plutonium lodged in the lungs has a different biological consequence from plutonium lodged in the reproductive organs. One can also consider exposures to X-rays, gamma rays, alpha or beta particles and neutrons separately, taking each as internal or external to the body.
There are further differences in health effects based on differences between people receiving the radiation. Special consideration needs to be given to those who, because of heredity or previous experience, are more susceptible to further damage than the norm or average. Special consideration should be given to an embryo or foetus, a young child, the elderly or those chronically ill.
The severity of health effects caused by internal exposures will depend on the biological characteristic of the radioactive chemical and the length of time it may be expected to reside in the body. Radioactive cesium, for example, lodges in muscles and is probably completely eliminated from the body in two years. Radioactive strontium lodges in bone and remains there for a lifetime, constantly irradiating the surrounding cells. The usual time required by the body to rid itself of half the radioactive chemical is called the `biological half-life' of that chemical.
Some radiation health effects are observable in the persons exposed some effects are only seen in their children or grandchildren because the damage was to sperm or ovum.
X-rays, gamma rays and neutrons are able to inflict harm on humans even when the radioactive chemical emitting them is outside the body. Beta particles outside the body can cause serious burns and other skin anomalies, including skin cancer. Ionising radiations emitted from within the body by radioactive chemicals taken in by inhalation, ingestion or absorption are even more damaging because they are so close to delicate cell structures. The body is not able to distinguish between radioactive and nonradioactive chemicals and will as readily incorporate the one as the other into tissue, bone, muscle or organs, identifying them as ordinary nutrients. The radioactive chemicals remain in the body until biologically eliminated in urine or faeces, or until they decay into other chemical forms (which may or may not be radioactive). These daughter products and their chemical and radiological properties may be quite different from those of the parent radioactive chemical, for example, radioactive carbon decays into nitrogen. Radiochemical analysis of urine or faeces is the preferred test for most types of internal contamination with alpha or beta particles.

The chaotic state induced within a living cell when it is exposed to ionising radiation has been graphically described by Dr Karl Z. Morgan as a `madman loose in a library'.[4] The result of cell exposure to these microscopic explosions with the resultant sudden influx of random energy and ionisation may be either cell death or cell alteration. The change or alteration can be temporary or permanent. It can leave the cell unable to reproduce (or replace) itself. Radiation damage can cause the cell to produce a slightly different hormone or enzyme than it was originally designed to produce, still leaving it able to reproduce other cells capable of generating this same altered hormone or enzyme. In time there may be millions of such altered cells. This latter mechanism, called biological magnification, can cause some of the chronic diseases and changes we usually associate with old age. One very specific mutation which can occur within the cell is the destruction of the cell's mechanism for resting which normally causes it to cease reproductive activities after cell division. This inability to rest results in a runaway proliferation of cells in one place, which, if not destroyed, will form a tumour, either benign or malignant. The abnormal proliferation of white blood cells is characteristic of leukaemia red blood cell proliferation results in what is called polycythemia vera.
If the radiation damage occurs in germ cells, the sperm or ovum, it can cause defective offspring. The defective offspring will in turn produce defective sperm or ova, and the genetic `mistake' will be passed on to succeeding generations, reducing their quality of life until the family line terminates in sterilisation and/or death.[5] A blighted or abnormal embryonic growth can result in what is called a hydatidiform mole instead of a baby.
Exposure to radiation is also known to reduce fertility, i.e. women become unable to conceive or give birth.
Radiation can also damage an embryo or foetus while it is developing within the mother's womb. This is called teratogenic damage, or the child is said to have a congenital malformation rather than genetic damage. This means the damage is not automatically transmitted. For example, a deaf person, made so by a pre-birth injury, may have children with normal hearing.
The damage done within cells by random releases of the energy of photons, alpha, beta or neutron particles can occur indirectly through an effect called ionisation. As the energised photons or particles speed through the cells, they give energy to the electrons of chemicals already within the cells, enabling some electrons to break free from the rest of the atom or molecule to which they are attached. On the macro-level this would be comparable to an atomic explosion of a magnitude great enough to drive the earth or another planet out of its orbit around the sun. What was an electrically neutral atom or molecule is split into two particles -- a larger positively charged atom or molecule missing one of its electrons, and a small negatively charged electron expelled from its orbit around the nucleus of the atom. Both are called ions and the process is called ionisation.
The complex molecules making up living organisms are composed of long strands of atoms forming proteins, carbohydrates and fats. They are held together by chemical bonds involving shared electrons. If the ionising radiation displaces one of the electrons in a chemical bond, it can cause the chain of atoms to break apart, splitting the long molecule into fragments, or changing its shape by elongation. This is an `ungluing' of the complex chemical bonds so carefully structured to support and perpetuate life. The gradual breakdown of these molecular bonds destroys the templates used by the body to make DNA and RNA (the information-carrying molecules in the cell) or causes abnormal cell division. The gradual natural breakdown of DNA and RNA is probably the cellular phenomenon associated with what we know as `ageing'. It occurs gradually over the years with exposure to natural background radiation from the radioactive substances which have been a part of the earth for all known ages. There is evidence that exposure to medical X-rays accelerates this breakdown process.[6] There is ample reason to think that fission products lodged within the body will cause the same kind of acceleration of ageing. However, unlike medical X-rays, these radioactive chemicals damage cells by their chemical toxicity as well as their radiological properties.
The gradual breakdown of human bio-regulatory integrity through ionising and breakage of the DNA and RNA molecules gradually makes a person less able to tolerate environmental changes, less able to recover from diseases or illness, and generally less able to cope physically with habitat variations.
When the DNA of germ plasm is affected by radiation it can result in chromosomal diseases, such as trisomy 21, more commonly known as Down's Syndrome. Mentally retarded children, victims of Down's Syndrome, have been reported in Kerala, India, an area of high natural radioactivity.[7] Recently, cases of Down's Syndrome have been tentatively linked to women exposed to radioactive releases from the large plutonium fire at Sellafield (Windscale) in 1957.[8] While Down's Syndrome babies have long been associated with births to older women (those with higher accumulated exposure to natural background radiation),[9] the Sellafield-related cases involve women with an average age of 25 years.
So far we have considered the types of ionising radiation, the location of the source outside or within the body, and the difference between exposures to different parts of the body or to different people of various ages and states of health. These will all be important considerations underlying standard setting. Next, we need to be able to measure radiation, i.e. to quantify exposure.

One way to approach the measurement of radiation is to count the number of nuclear transformations or explosions which occur in a given unit of radioactive substance per second. This measure is usually standardised to radium, the first radioactive substance to be discovered and widely used. One gram of radium undergoes 3.7 x 10^10 nuclear transformations or disintegrations per second. The activity of 1 gram of radium is called 1 curie (Ci), named for Madame Marie Curie, a Polish-born French chemist (1867-1934). Marie Curie discovered the radioactivity of thorium, polonium and radium by isolating radium from pitchblende. She and her daughter Irene were among the earliest known radiation victims, both dying of aplastic anaemia.
In recent radiation protection guides, the curie is being replaced by the becquerel, which indicates one atomic event per second. One gram of radium would equal 1 curie of radium or 3.7 x 10^10 becquerels of radium.
The energy released in nuclear disintegrations has the ability to do work, i.e. to move matter. In physics, the erg is a very small unit of work done. Lifting 1 gram of radium 1 centimetre requires 980 ergs of work. Any material exposed to the force from nuclear disintegrations at a rate of 100 ergs/gm is said to absorb one rad, i.e. radiation absorbed dose. There is no direct conversion from curies, which is related to the number of atomic events, to the rad dose, which is energy absorbed in tissue. The curie gives one an estimate of the number of microscopic transformations or explosions per second and the rad is an estimate of the energy release, absorbed by the surrounding tissue. On the macro-level, the word `explosion' tells us only of an event in time. A dynamite explosion or hydrogen bomb explosion adds information about the energy released.
Sometimes radioactivity is measured in counts per minute on a Geiger counter. A nuclear transformation within an energy range measured by the instrument and close enough to the instrument causes a noise or `count'. Most Geiger counters cannot detect alpha particle emitters like plutonium.
The radioactivity of elements which experience nuclear disintegrations is measured relative to radium. For example, it would take more than 1 million grams of uranium to be equivalent in radioactivity, i.e. to have the same number of nuclear events per second as 1 gram of radium has per second. Both 1 million grams of uranium and 1 gram of radium would be measured as 1 Ci. It has been the custom in the past to limit human exposure to uranium more for its toxic chemical properties (it is a heavy metal) than for its radioactivity. This practice may have underestimated damage caused by the biological storing of uranium in the liver.
When uranium decays, it passes through about 12 radioactive forms, called daughter products, before reaching a stable chemical form of lead. One of the radioactive daughter products of uranium is radium. Uranium released into drinking water or incorporated into food and human tissue today will eventually plague the world as radium and its other disintegration products: radon gas and the radioactive forms of polonium, lead and bismuth. The environmental and biochemical forces which may tend to reconcentrate these toxic materials in living cells are not well known. Although uranium occurs naturally, it has become much more available for entering into water, food, living cells and tissue since the mining boom which began shortly after the Second World War.
The activity which takes place in the nucleus of the uranium or radium atom is a `haphazard' event obeying the laws of random probabilities. An atom is characterised by its atomic number, that is, the positively charged particles in its nucleus, and by its atomic mass, expressed in atomic mass units (similar to the concept of weight), which includes both the number of protons (the atomic number) and the number of neutrons in the nucleus. Carbon, the most frequently occurring chemical in living material, is taken as having exactly 12 atomic mass units and other atoms are measured in relation to this. Carbon 14, which is radioactive, has two extra neutrons in its nucleus.
Hydrogen, another example, has an atomic number of 1 and an atomic mass of 1. Isotopes of hydrogen have the same atomic number (that is, the same number of positively charged particles in the nucleus and electrons in orbit around the nucleus) but a higher atomic mass. Deuterium or hydrogen 2, an isotope of hydrogen, has an atomic number of 1 and an atomic mass of 2. It is not radioactive. The increased atomic mass is due to an added neutron in the nucleus. Deuterium is in the `heavy water' used in the Canadian CANDU nuclear reactor. Hydrogen 3, called tritium, is radioactive, with two neutrons and a proton in the nucleus. It is produced in a nuclear reaction.
When radium 226 decays, it loses a positively charged alpha particle from its nucleus. An alpha particle has two protons (positive electrical charges) and a mass of 4 atomic units. This means a reduction in both radium's atomic number and atomic mass. Loss of the alpha particle changes radium 226 (transmutes it) into another element, radon 222. While radium 226 is a radioactive solid under normal conditions, radon 222 is a radioactive gas. Loss of one or more protons changes the chemical element into a different chemical. Absorption or loss of a neutron gives an isotope of the same chemical since chemical properties are determined by the number of protons and electrons in an atom.
The time required for half of any amount of radium 226 to transmute to radon 222 by these small explosions which emit alpha particles is 1,622 years. This is called the physical half-life of radium. Half of the radium literally disappears in that length of time, but radon gas is produced to replace it. Radon gas is radioactive and more mobile in air and water (it dissolves) than the solid radium. The half-life of radon is 3.82 days, after which half the gas will have disintegrated, again releasing alpha particles and transmuting into radioactive polonium 218, which is a solid. With a wind of 10 mph (or kph), the radon gas could travel 1,000 miles (or kilometres) from the point of origin before half of it would have decayed into its solid daughter products and been deposited on soil, leafy vegetables, tobacco, groundwater, human skin, lung tissue, etc. If the material receiving the radioactive daughter product is living, then it can carry the particles into its cells. Such contamination cannot be washed off.
When a negatively charged beta particle is released, there is a transmutation in which a neutron in the nucleus of the atom splits into a proton and an electron, the proton remaining in the nucleus and the electron given off as a fast-moving microscopic bullet. Beta particles are extremely small. The mass of an alpha particle is about 7,400 times that of a beta particle. Thorium 234 decays to uranium 234 (with a short-lived radioactive intermediary) by losing beta particles. Uranium and thorium are different elements, but have the same mass (atomic weight) since a neutron and proton have about the same mass. The thorium neutron becomes the uranium proton. The half-life of thorium 234 is 24.1 days, while the half-life of uranium 234 is 2.50 x 10^5, or 250,000 years. As was pointed out earlier, uranium nuclear events are not as frequent as those in radium, although they are destructive when they occur.
Given 12 grams of thorium 234, we would have 6 grams after 24.1 days, 3 grams after 48.2 days, 1.5 grams after 72.3 days, 0.75 grams after 96.4 days, etc. At the same time, the stock of uranium 234 would be increasing as the thorium decays into the new radioactive chemical.
There is no simple physical or chemical process such as temperature change or chemical bonding which can prevent these radioactive elements from decaying. Their nucleus is unstable and because all elements seek a stable low-energy state, they must at some time release particles in an effort to reach a resting state. The decay takes place in the nucleus of the atom regardless of whether the atom exists singly or is part of a molecule is in the solid, liquid or gaseous state is within the body or outside, and so on. The decay product after a radioactive disintegration may itself be radioactive, so disintegration does not put an end to the biological problems generated by these small explosions. This decay process must be taken into account when estimating the biological effects of internal exposure to radioactive material. Inhaled radon gas quickly becomes radioactive lead, bismuth or polonium in the bloodstream.
One should not confuse physical half-life with biological half-life, i.e. the time required to eliminate half of the material from the body through exhalation, urine or faeces. Cesium 137 and strontium 90 both have physical half-lives of almost thirty years, but cesium 137 is normally excreted from the body within two years while strontium 90 can be incorporated in bone for a lifetime.
One more measure needs to be introduced before radiation protection guides can be understood. Since the various kinds of radiation exposures need to be evaluated for biological impact and not just for the amount of energy absorbed by the tissue, the term rem, roentgen equivalent man (or woman), was introduced. The rem dose is the rad dose times a quality factor Q. For external radiation Q is usually taken as 1, and rads and rems are used interchangeably. However, to reflect the greater biological damage done by alpha particles when inside the body, the rad dose may be multiplied by 20 to give the rem dose. This is another way of saying that the alpha particle does damage of an order of magnitude (20 times) greater when lodged within a tissue, bone or organ. For example, alpha particles giving a 2 rem (or rad) dose to skin would give a 40 rem dose to sensitive lung tissue when inhaled.
Theoretically, the rem dose measures equivalent biological effect, so that damage from X-rays, for example, would be the same as damage from alpha particles, when the dose in rem was the same. Unfortunately, living systems are too complex for such an approach to provide anything more than a good guess.
Sometimes references are made to a `fifty-year effective dose equivalent'. This is the full dose that would be received from an internal radionuclide if the dose were given at one time instead of being spread over two to fifty years.

Linear Energy Transfer (LET)

Measurement of the number of ionisations which radiation causes per unit distance as it traverses the living cell or tissue is called the linear energy transfer of the radiation. The concept involves lateral damage along the path, in contrast to path length or penetration capability. Medical X-rays and most natural background radiation are low LET radiation, while alpha particles have high LET. On the average, fission fragments have high LET.
The density of ionisation causes special problems in sperm and ova because the damage (protein breakage) is concentrated within a few cells. The two-year sterility of Japanese fishermen exposed to fallout from the 1954 hydrogen bomb test is probably an example of this effect. Sperm and the cells which produce sperm were damaged beyond their capability of prompt repair.
As a young girl in St George, Utah, USA, Elizabeth Catalan used to stand outdoors and watch the mushroom clouds raised by the Nevada nuclear tests float overhead. She has never been able to have children. She, like some other women in St George, is unable to carry a foetus to birth. Elizabeth's father, president of a local college, died prematurely of leukaemia. He used to go horse-riding with three friends and was frequently outside when the grey clouds laden with radioactive chemicals went over. Three of the four men are now dead from cancer.
Elizabeth's sister died in her late twenties of a thyroid disease which may have been caused by the radioactive iodine released in the atomic blasts. Elizabeth and her mother attribute many of their abnormal health problems, and those of family and friends, to the atomic fallout. No government studies have been undertaken to confirm or deny these claims. However, the situation was so widely recognised as abnormal by the local population that the Governor of Utah has filed a court claim against the US Federal Government for wrongful deaths of the people of Utah. About a thousand individual damage claims have entered the courts in the USA, and as part of the trial preparations Dr Carl Johnson undertook a detailed study of the Mormon population of Utah exposed to the fallout. It is reasonable to conclude that the health problems reported by the people of Utah are typical of what could be expected on the basis of theoretical radiobiology.[10]
On 10 May 1984, US District Court Judge Bruce S. Jenkins ruled on the first twenty-four claims of US government negligence in its conduct of nuclear testing. He has awarded $2.6 million in damages to ten claimants. This landmark, 489-page, carefully worded decision is expected to be appealed against by the US Federal Government.
In order to have a quantitative sense of the frequency of the different cell effects caused by radiation exposure, imagine a colony of 1,000 living cells exposed to a 1 rad X-ray (about the dose for one X-ray spinal examination). There would be two or three cell deaths, two or three mutations or irreparable changes in cell DNA and about 100,000 ionisations in the whole colony of cells -- ranging from 11 to 460 ionisations per cell.[11] While cells can repair some damage, no one claims that there is perfect repair even after only one such X-ray.
A comparable 1 rad exposure to neutrons which have higher linear energy transfer (LET) would be expected to cause more cell deaths and more mutations. The ionisations caused would range from 145 to 1,100 per cell.
Alpha particles which occur naturally would cause roughly 10 times as many cell deaths and mutations, and 3,700 to 4,500 ionisations per cell. Alpha particles have high linear energy transfer.
The average number of cell deaths and mutations caused by fresh fission particles (i.e. those present soon after detonation of a nuclear bomb) would be even greater, with the ionisations as frequent as 130,000 per cell.[12] In nuclear reactors, most of these extremely high-energy early fission fragments are enclosed within the fuel rod. In a nuclear bomb blast, they are all released but they decay very quickly and do not persist long in the environment.
If instead of thinking of a colony of living cells, we think of a person exposed to 1 rad (again about the skin dose from one spinal X-ray) of 1 MeV (million electron volts) energy, this corresponds to 2.2 billion (US) photons per cm^2 acting on the body. In the words of Karl Morgan, `It is inconceivable that all the billions of irradiated and damaged cells would be completely repaired.'[13] This unrepaired damage accumulates, eventually causing a reduction in the level of health that is normal for a particular age.
Stated very simply, ionising radiation seriously disrupts the chemistry of the cell. It can also kill or permanently change the cell. Every exposure to ionising radiation has this effect, and it is not possible for the body to perfectly repair all of the damage. Whether or not the residual unrepaired damage is of concern to the individual exposed is a personal value judgment. It is not at all clear that ordinary people find the damage `acceptable" unless it initiates a fatal cancer, and yet this is the basis on which radiological safety standards are set in all nations of the world.
R. M. Sievert, the famous radiologist, who had supervised radiation therapy since 1926 at the Karolinska Institute in Stockholm, pointed out at an international meeting in 1950 that `there is no known tolerance level for radiation'.[14] A tolerance level is a level below which there is no damage (sometimes called a threshold). A safety level is ordinarily a fraction (one-tenth) of the tolerance level.[14]

Cell Damage Expressed as a Health Problem

An example to show the connection between cell damage and observable illness in the person exposed might help in understanding the problems posed by radionuclide (radioactive chemical) uptake, i.e. their ingestion, inhalation or absorption with food, air and water, into human bodies, with subsequent cell damage. The thyroid gland contains cells which produce thyroid hormone, which when released into the bloodstream causes the body functions such as breathing, digesting and reacting to stress to proceed at a certain rate. If the thyroid is `overactive', one might notice in the person increased pulse rate, nervousness, excitability, loss of body weight and, in females, more frequent menstruation. Such a person is often called `hyperactive' (hyper-thyroidism). A normal amount of thyroid hormone in the blood produces a normally active individual. An `underactive' or `hypoactive' thyroid can result in sluggishness, listlessness, weight gain and irregular and/or infrequent menstrual flow in women (hypothyroidism).
If radioactive iodine (I 131 or I 129) is ingested with food it will enter the blood and tend to accumulate in the thyroid. Radioactive iodine emits high-energy gamma radiation which can destroy thyroid cells, thus reducing total thyroid hormone production in the individual so affected.
A small amount of radioactive iodine would probably kill only a few cells and have little or no noticeable effect on health. However, if many cells are destroyed or altered, the hormone level would noticeably drop or the hormone itself would be slightly changed. The individual would become lethargic and gain weight. If properly diagnosed and severe enough to require medical intervention, this hypoactive thyroid condition can be controlled with artificially ingested thyroid hormone. A mild exposure experienced by a large population could cause a decrease in average thyroid hormone levels and an increase in average body weight, such as is occurring now in the North American population. The USA has been polluted with nuclear industries since 1943 and with radioactive iodine from weapon testing since 1951. Radioactive iodine is routinely released in small quantities by nuclear power plants and in large quantities by nuclear reprocessing plants. It is not part of the natural human environment. The connection between this pollution and the overweight problem has, unfortunately, never been seriously researched. There is no evidence to confirm or deny the hypothesis, but weight increase is a well-known biological response to radioactive iodine. The hypothesis is certainly plausible under the circumstances.
It is possible for thyroid cells to be altered but not killed by the radiation. The cellular growth mechanism may be damaged, allowing a runaway proliferation of cells. This results in a thyroid tumour, either cancerous (malignant), or non-cancerous (benign). Other possible radiation damage includes changes in the chemical composition of the individual's thyroid hormone, altering its action in the body and causing clinically observable symptoms not easily diagnosed or corrected.
There is an extremely remote possibility that these changes will be desirable, but the overall experience of randomly damaging a complex organism like the human body is that it is destructive of health.
An atomic veteran who participated in the nuclear tests which were conducted by the USA in the Bikini atoll in the late 1940s reported that he gained 75 lbs in the four years following his participation. The doctor diagnosed his problem as hypothyroidism. He also suffered from high blood pressure, chronic asthma and frequent bouts of bronchitis and pneumonia. He has had six tumours diagnosed since 1949, when he returned home from military service. Four have been surgically removed.
Damage to the thyroid of a developing foetus can cause mental retardation and other severe developmental anomalies.[15]
Other radionuclides will lodge in other parts of the body. If the trachea, bronchus or lung are exposed, the damage eventually causes speech or respiratory problems. If radioactive particles lodge in the stomach or digestive tract, the heart, liver, pancreas or other internal organs or tissues, the health problems will be correspondingly different and characteristic of the organ damaged. Radionuclides which lodge in the bone marrow can cause leukaemia, depression of the immune system (i.e. the body's ability to combat infectious diseases) or blood diseases of various kinds.
If the radiation dose is high, there is extensive cell damage and health effects are seen immediately. Penetrating radiation doses at 1,000 rad or more cause `frying of the brain' with immediate brain death and paralysis of the central nervous system. This is why no one dared to enter the crippled Three Mile Island nuclear reactor building during the 1979 accident. An average of 30,000 roentgens (or rads) per hour were being reported by instruments within the containment building. This would convert to a 1,000 rad exposure for two minutes spent inside the building. Such a dose to the whole body is invariably fatal.
The radiation dose at which half the exposed group of people would be expected to die, i.e. the 50 percent lethal dose, is 250 rad. The estimate is somewhat higher if only young men in excellent health (e.g. soldiers) are exposed. Between 250 and 1,000 rad, death is usually due to gross damage to the stomach and gut. Below 250 rad death is principally due to gross damage to the bone marrow and blood vessels. A dose of about 200 rad to a foetus in the womb is almost invariably fatal.
Penetrating radiation in doses above 100 rad inflicts severe skin burns. Lower doses produce burns in some people. Vomiting and diarrhoea are caused by doses above about 50 rad. There are some individuals who are more sensitive to radiation, however, showing typical vomiting and diarrhoea radiation sickness patterns with doses as low as 5 rad. An individual may react differently at different times of life or under different circumstances. Below 30 rad, for most individuals, the effects from external penetrating radiation are not immediately felt. The mechanism of cell damage is similar to that described for minute quantities of radioactive chemicals which lodge within the body itself, and our bodies are incapable of `feeling' damage to or death of cells. Only when enough cells are damaged to interfere with the function of an organ or a body system does the individual become conscious of the problem.
By sharpening our perceptions more subtle radiation effects can often become observable where once they went unnoticed. For example, a series of X-rays received by a young child may cause temporary depression of the white blood cells, and ten days to two weeks after the exposure the child will get influenza or some other infectious disease. Ordinarily the parent views the two events as unconnected.
Sometimes one can observe a mutation in a person who has experienced loss of hair after radiation therapy to kill tumour cells: hair that was formerly very straight can be curly when it grows again.
A plant whose flowers are normally white with red tips but which begins to form uniformly red flowers has mutated. Such an event has been observed by persons living in the vicinity of Sellafield in the United Kingdom.
The use of radiation therapy to destroy malignant cells also has observable results. It is rather like surgery in that it is deliberately used to kill the unwanted tumour cells.

Probable Health Effects resulting
from Exposure to Ionising Radiation

Dose in rems
(whole body)
Health effects
1,000 or more Immediate death.
`Frying of the brain'.
600-1,000 Weakness, nausea, vomiting and diarrhoea followed by apparent improvement. After several days: fever, diarrhoea, blood discharge from the bowels, haemorrhage of the larynx, trachea, bronchi or lungs, vomiting of blood and blood in the urine. Death in about 10 days. Autopsy shows destruction of hematopoietic tissues, including bone marrow, lymph nodes and spleen swelling and degeneration of epithelial cells of the intestines, genital organs and endocrine glands.
250-600 Nausea, vomiting, diarrhoea, epilation (loss of hair), weakness, malaise, vomiting of blood, bloody discharge from the bowels or kidneys, nose bleeding, bleeding from gums and genitals, subcutaneous bleeding, fever, inflammation of the pharynx and stomach, and menstrual abnormalities. Marked destruction of bone marrow, lymph nodes and spleen causes decrease in blood cells especially granulocytes and thrombocytes. Radiation-induced atrophy of the endocrine glands including the pituitary, thyroid and adrenal glands.
    From the third to fifth week after exposure, death is closely correlated with degree of leukocytopenia. More than 50% die in this time period.
    Survivors experience keloids, ophthalmological disorders, blood dyscrasis, malignant tumours, and psychoneurological disturbances.
150-250 Nausea and vomiting on the first day. Diarrhoea and probable skin burns. Apparent improvement for about two weeks thereafter. Foetal or embryonic death if pregnant. Symptoms of malaise as indicated above. Persons in poor health prior to exposure, or those who develop a serious infection, may not survive.
    The healthy adult recovers to somewhat normal health in about three months. He or she may have permanent health damage, may develop cancer or benign tumours, and will probably have a shortened lifespan. Genetic and teratogenic effects.
50-150 Acute radiation sickness and burns are less severe than at the higher exposure dose. Spontaneous abortion or stillbirth. Tissue damage effects are less severe. Reduction in lymphocytes and neutrophils leaves the individual temporarily very vulnerable to infection. There may be genetic damage to offspring, benign or malignant tumours, premature ageing and shortened lifespan. Genetic and teratogenic effects.
10-50 Most persons experience little or no immediate reaction. Sensitive individuals may experience radiation sickness. Transient effects in lymphocytes and neutrophils. Premature ageing, genetic effects and some risk of tumours.
0-10 None Premature ageing, mild mutations in offspring, some risk of excess tumours. Genetic and teratogenic effects.

In 1943, Hermann Müller received a Nobel Prize for his work on the genetic effects of radiation and was a dominant figure in developing early radiation exposure recommendations made by the International Commission on Radiological Protection (ICRP).[16] He showed through his work with Drosophila, a fruit fly, that ionising radiation affects not only the biological organism which is exposed but also the seed within the body from which the future generations are formed.
In 1964 Hermann Müller published a paper, `Radiation and Heredity', spelling out clearly the implications of his research for genetic effects (damage to offspring) of ionising radiation on the human species.[17] The paper, though accepted in medical/biological circles, appears not to have affected policy makers in the political or military circles who normally undertake their own critiques of published research. Müller predicted the gradual reduction of the survival ability of the human species as several generations were damaged through exposure to ionising radiation. This problem of genetic damage continues to be mentioned in official radiation-health documents under the heading `mild mutations'[18] but these mutations are not `counted' as health effects when standards are set or predictions of health effects of exposure to radiation are made. There is a difficulty in distinguishing mutations caused artificially by radiation from nuclear activities from those which occur naturally from earth or cosmic radiation. A mild mutation may express itself in humans as an allergy, asthma, juvenile diabetes, hypertension, arthritis, high blood cholesterol level, slight muscular or bone defects, or other genetic `mistakes'. These defects in genetic make-up leave the individual slightly less able to cope with ordinary stresses and hazards in the environment. Increasing the number of such genetic `mistakes' in a family line, each passed on to the next generation, while at the same time increasing the stresses and hazards in the environment, leads to termination of the family line through eventual infertility and/or death prior to reproductive age. On a large scale, such a process leads to selective genocide of families or species suicide.[19]
It soon became obvious that the usual method determining a tolerance level for human exposure to toxic substances was inappropriate for ionising radiation. The health effects were similar to normally occurring health problems and were quite varied, ranging from mild to severe in a number of different human organ systems, and their appearance could be delayed for years or even generations.

Permissible Levels of Exposure

The US National Council on Radiation Protection and Measurement gave expression to the theoretical resolution of this human dilemma by articulating the implicit reasoning behind subsequent radiation protection standards development:[20]

    A value judgment which reflects, as it were, a measure of psychological acceptability to an individual of bearing slightly more than a normal share of radiation-induced defective genes.

This is now an internationally accepted approach to setting standards for toxic substances when no safe level of the substance exists.

In short, this elaborate philosophy recognises the fact that there is no safe level of exposure to ionising radiation, and the search for quantifying such a safe level is in vain. A permissible level, based on a series of value judgments, must then be set. This is essentially a trade-off of health for some `benefit' -- the worker receives a livelihood, society receives the military `protection' and electrical power is generated. Efforts to implement these permissible standards would then logically include convincing the individual and society that the `permissible' health effects are acceptable. This has come to mean that the most undesirable health effects will be infrequent and in line with health effects caused by other socially acceptable industries. Frequently, however, the worker and/or public is given the impression that these `worst' health effects are the only individual health effects. A second implication of the standards-based-on-value-judgments approach is that unwanted scientific research resulting in public scrutiny of these value judgments must be avoided.
The genetic effect considered by standard setters as most unacceptable is serious transmittable genetic disease in live-born offspring. These severely damaged children are usually a source of suffering for the family and an expense for society which must provide special institutions for the mentally and physically disabled. Severely handicapped people rarely have offspring many die, are sterile or are institutionalised before they are able to bear children. Workers and the public are told that the probability of having such severely damaged offspring after radiation exposure within permissible levels is slight. By omission, a mildly damaged child or a miscarriage is implied to be `acceptable'.

From a column in the Yomiuri Shinbun (19 January 1965 evening edition)

A nineteen-year-old girl in Hiroshima committed suicide after leaving a note: `I caused you too much trouble, so I will die as I planned before.' She had been exposed to the atomic bomb while yet in her mother's womb nineteen years ago. Her mother died three years after the bombing. The daughter suffered from radiation illness her liver and eyes were affected from infancy. Moreover, her father left home after the mother died. At present there remain a grandmother, age seventy-five an elder sister, age twenty-two and a younger sister, age sixteen. The four women had eked out a living with their own hands. The three sisters were all forced to go to work when they completed junior high school. This girl had no time to get adequate treatment, although she had an A-bomb victim's health book.
As a certified A-bomb victim, she was eligible for certain medical allowances but the [A-bomb victims' medical care] system provided no assistance with living expenses so that she could seek adequate care without excessive worry about making ends meet. This is a blind spot in present policies for aiding A-bomb victims. Burdened with pain and poverty, her young life had become too exhausted for her to go on . . . .
There is something beyond human expression in her words `I will die as I planned before.'

Quoted in Kenzaburo Oe, Hiroshima Notes, YMCA Press Tokyo (English translator Toshi Yonezawa English editor David L. Swain).

Standard setters judge that the most severe damage done directly to the person exposed is a fatal radiation-induced cancer, and again, this is a rare occurrence when exposure is within permissible levels. All other direct damage is by omission considered `acceptable'.
In its 1959 report recommending occupational standards for internal radiation doses (i.e. radioactive chemicals which are permitted to enter the body through air, water, food or an open wound), the International Commission on Radiological Protection (ICRP) formed the following definition:

This might be paraphrased to say that the general public (governments) may be willing to accept the number of blind, deaf, congenitally deformed, mentally retarded and severely diseased children resulting from the permissible exposure level. Defined this way, the problem becomes primarily an economic one, since society needs to estimate the cost of providing services for the severely disabled. Once reduced to an economic problem, some nations may choose to promote early detection of foetal damage during pregnancy and induced abortion when serious handicap is suspected. When a foetus is aborted prior to sixteen weeks' gestation the event may not need to be reported and included in vital statistics. It becomes a non-happening, and the nation appears to be in `good health', having reduced the number of defective births.
Mild mutations, such as asthma and allergies, are ordinarily not even counted as a `cost' of pollution. The economic burdens, `health costs', fall more on the individual and family than on the government. Their pain and grief do not appear in the risk/benefit equation. Parents and children are unaware of the `acceptable burden' philosophy.
The prediction of the magnitude of the burden of severe genetic ills on an exposed population is essential to this philosophy. However, the data accumulated at Hiroshima and Nagasaki did not give clear answers. Either through ineptitude or loss of survivors of the bombing, who died before their story was told, the researchers failed to find any severe genetic ills clearly attributable to the parental exposure to radiation at low doses.[21] Probably the more fragile individuals in the population died from the blast, fire and trauma of the bombs, the women not surviving long enough to become pregnant.[22]
Governments could not use the research on genetic damage in children of medical radiologists,[23] although this damage was measurable, because, in the early days, radiation exposure to physicians was not measured. No quantitative dose/response estimates could be derived.
Animal studies of radiation-related genetic damage abounded, and the recommending body, ICRP, used (and still uses) mouse studies as a basis of its official predictions of the severe genetic effects of ionising radiation in humans.
As late as 1980, a US National Academy of Science publication from its committee on the Biological Effects of Ionising Radiation[24] stated:

These mouse studies are used as the basis of prediction, and permissible doses are set so that the expected number of severe transmittable genetic effects in children of those exposed could be presumed to be an acceptable burden for governments choosing a nuclear strategy.
The introductory section of ICRP Publication 2, 1959, states:

Mild mutations are notably happenings of a minor nature, normally neither reported nor monitored in the population. They are likely to be statistically hidden by normal biological variations and unconnected in the mind of the individual or his/her physician with the exposure. The publication continues:

In spite of this clarity, no such statistical audit of all health effects including chronic diseases in exposed people and mild mutations in their offspring has ever been done. More than 25 years have expired since this document was published and the world is more than 35 years into the nuclear age.
As late as 1965, ICRP Publication 9[25] stated:

The committee protected itself against accusations of wrongdoing but failed to protect the public from its possible error. It defines its role as recommending, with the responsibility of action to protect worker and public health resting with individual national governments. Governments in turn tend to rely on ICRP recommendations as the best thought of internationally respected experts.
In spite of this uncertainty about responsibility and safety levels for exposure of the public, 5 rem per year, rather than per 30 years, was permitted for workers in the nuclear industry. The 5 rem per 30 years was set as the average dose to a population, with a maximum of 0.5 rem per year (15 rem per 30 years) for any individual member of the public.
For twenty years, between 1945 and 1965, health research on the effects of ionising radiation exposure has focused on estimating (not measuring) the number of excess radiation-induced fatal cancers and excess severe genetic diseases to be expected in a population (i.e. a whole country) given the average estimated exposure to radiation for the country. Disputes among scientists usually have to do with the magnitude of these numbers. Omitted from this research are other radiation-related human tragedies such as earlier occurrence of cancers which should have been deferred to old age or even might not have occurred at all because the individual would have died naturally before the tumour became life-threatening. These are not excess cancers, they are accelerated cancers. This approach also omits other physiological disorders such as malfunctioning thyroid glands, cardio-vascular diseases, rashes and allergies, inability to fight off contagious diseases, chronic respiratory diseases and mildly damaged or diseased offspring. The implications of such `mild' health effects on species survival seem to have either escaped the planners of military and energy technology, or to have been deliberately not articulated. Other obvious limitations of this national averaging approach include the failure to deal with global distribution of air and water with the result that deaths and the cumulative damage to future generations are not limited to one country.
The usual procedure for setting the standard for a toxic substance or environmental hazard is to decide the relevant medical symptoms of toxicity and determine a dose level below which these symptoms do not occur in a normal healthy adult. This cut-off point is sometimes called the tolerance level and it represents a sort of guide to the human ability to compensate for the presence of the toxic substance and maintain normal health. The tolerance level for a substance, if one can be determined, is then divided by a factor (usually 10) to give a safe level. This allows for human variability with respect to the tolerance level and also for biological damage which may occur below the level at which there are visible signs of toxicity, i.e. sub-clinical toxicity.
Human experience with ionising radiation had been recorded for more than fifty years prior to the nuclear age, the early history of handling radioactive material having been fraught with tragedy. The discoverer of the X-ray, W. K. Roentgen, died of bone cancer in 1923, and the two pioneers in its medical use, Madame Marie Curie and her daughter, Irene, both died of aplastic anaemia at ages 67 and 59 respectively. At that time, bone marrow studies were rarely done, and it was difficult, using blood alone, to distinguish aplastic anaemia from leukaemia. Both diseases are known to be radiation-related. Stories of early radiologists who had to have fingers or arms amputated abound. There were major epidemics among radiation workers, such as that among the women who painted the radium dials of watches to make them glow in the dark. Finally, there were the horrifying nuclear blasts in Hiroshima and Nagasaki.
The painful period of growth in understanding the harmful effects of ionising radiation on the human body was marked by periodic lowering of the level of radiation exposures permitted to workers in radiation-related occupations. For example, permissible occupational exposure to ionising radiation in the United States was set at 52 roentgen (X-ray) per year in 1925,[26] 36 roentgen per year in 1934,[27] 15 rem per year in 1949[28] and 5 to 12 rem per year from 1959 (depending on average per year over age 18) to the present.[29] Recently there has been an effort to increase permissible doses of ionising radiation to certain organs such as thyroid and bone marrow[30] in spite of research showing the radiosensitivity of these tissues. This newer trend probably reflects economic rather than physiological pressures, especially given the lack of an acceptable audit of physiological cost.

Radiation Protection Standards

In 1952 the International Commission on Radiological Protection (ICRP) issued its recommendations for limiting human exposure to external sources of radiation. The newly formed organisation accepted the standard agreed upon by nuclear physicists from the USA, Canada and the UK after the Second World War.[31] In 1959 it issued its recommendations for limiting human exposure to internal sources of radiation. The early ICRP dose limits per year were: 5 rem to the whole body, gonads or active bone marrow 30 rem to bone, skin or thyroid 75 rem to hands, arms, feet or legs and 15 rem to all other body parts. These standards applied only to `man-made' sources, other than medical exposures for diagnostic or therapeutic purposes of benefit to the patient exposed.
ICRP Publication 2, in 1959, recommended no more than 5 rem per year external or internal exposure to the whole body due to inhalation, ingestion or absorption of radioactive chemicals into the body. Sometimes this was misinterpreted and workers were permitted to receive up to 5 rem internal and 5 rem external radiation exposure during one year. Another clause allowing averaging doses over years beyond age 18, gave excuse for still higher doses.
In terms of the amount of whole body dose received in a chest X-ray (about 0.03 rem at the present time), this recommendation for workers allowed the equivalent of 400 chest X-rays in some years with a 170 (present-day) chest X-ray average (external and internal) dose a year. Prior to 1970 some X-ray machines used in mass chest X-ray programmes gave as high as 3 rem per chest X-ray.
When one looks at dose to bone marrow, the permissible levels are even more troubling. By 1970 the average bone marrow dose for a chest X-ray was 0.001 to 0.006 rem averaging about 0.005 rem. In terms of dose to bone marrow, the ICRP radiation recommendation for workers permits up to the equivalent bone marrow dose of 1,000 chest X-rays per year.
ICRP recommended that members of the general public should receive no more than one-tenth of the occupational exposure or 0.5 rem per year, the equivalent bone marrow dose of about 100 present-day chest X-rays per year. The bone marrow dose is important for estimating the likelihood of causing bone cancer, leukaemia, aplastic anaemia or other blood disorders. Medical X-rays are less penetrating of bone than of soft tissue, making them valuable for `picturing' the bones. For this reason comparisons between radiation exposures of nuclear workers and medical X-ray exposures are more appropriately based on the bone marrow dose of each than on dose to soft tissue.
These radiation exposure recommendations stayed essentially the same until 1978, when in ICRP Publication 26 a recommendation was made to raise the levels of radiation permitted to humans from man-made sources of radiation (excluding that for medical purposes). For `internal consistency' of the recommendations there was some valid argument for scaling the standards for particular organ exposure in proportion to whole body exposure recommendations -- but scaling down as well as up would have accomplished this. For example, the ICRP reasoned that if the whole body could receive 5 rem per year, the active bone marrow should not be limited to 5 rem per year. This was used as a reason for increasing the permitted bone marrow dose from 5 rem to 42 rem with apparently little regard for the increased damage to bones and blood-producing organs.
ICRP Publication 26 also reiterates the need to allow human exposure in order to enjoy the `economic and social benefits' of the nuclear industries. It is difficult to understand how this conclusion was reached when so much new research is available documenting human illness associated with the present permissible exposure levels.[32] Perhaps, in view of contemporary scientific concern for lowering radiation exposures, ICRP Publication 26 recommendations are a political move to hold the line at present regulatory levels. At any rate, it appears to be a document with a political rather than a scientific purpose.
Some national regulatory agencies, such as the Atomic Energy Control Board in Canada, promptly implemented ICRP Publication 26 by increasing allowable radium levels in drinking water, thus reducing the clean-up cost for the uranium mining companies. Since some members of the national radiation protection community in Canada and elsewhere hold seats on ICRP, responsibility for what they recommend nationally cannot credibly be attributed to an international recommending body.

ICRP Publication 2 (1959) is one of special interest since it clearly states that radiation-induced severe genetic defects and cancer deaths resulting from the recommended standards would be expected to be rare and hardly distinguishable from `natural' variations due to non-radiation causes. The document goes on to point out that mild mutations in offspring and general ill health in those exposed would be the most frequent health effects of exposure, but these could not be `detected' except by epidemiological surveys. ICRP Publication 2 made no recommendation that this more subtle widespread degradation of public health be measured, although they mentioned that it could be measured.[33] At no time has there been an effort on the part of governments to document fully the more subtle health effects.
Workers, military service personnel and the general public have been given the impression that exposure to radiation involves a slight risk of dying of cancer and that one's chances of escaping this are better than the chances of escaping an automobile accident. The probabilities of early occurrence of heart disease, diabetes mellitus, arthritis, asthma or severe allergies -- all resulting in a prolonged state of ill health -- are never mentioned. Most people are unaware of the fact that ionising radiation can cause spontaneous abortions, stillbirths, infant deaths, asthmas, severe allergies, depressed immune systems (with greater risk of bacterial and viral infections), leukaemia, solid tumours, birth defects, or mental and physical retardation in children. Most of the above-mentioned tragedies affect the individual or family unit directly and society only indirectly. Dr R. Mole, a member of ICRP and the British NRPB, stated: `The most important consideration is the generally accepted value judgment that early embryonic losses are of little personal or social concern.'[34] There are similar value judgments made with respect to other health effects. The health problems are externalised, i.e. placed beyond the responsibility of government, and they are borne by individuals and their families.
The risk/benefit decision making which arose from balancing `health effects' against `economic and social benefit' is based on risk and benefit to society, i.e. governments, rather than cost to the individual or family unit. Value judgments have been made as to the level of health effects and deaths `acceptable' to the public. Because of military control of A-bomb studies and military need for personnel to handle radioactive materials, many of these value judgments were cloaked in secrecy for the sake of `national security'. The subject was made to seem complicated to outsiders the decisions were reserved for the experts. The now famous words of President Dwight D. Eisenhower, `Keep the public confused'[35] about nuclear fission so that the government could gain public acceptance of above-ground weapon testing in Nevada, have certainly been accomplished. A growing number of people in the USA and elsewhere have lost all faith in statements made by government officials, because of the scientific jargon used to mask the truth.
In the USA, external radiation exposure records (film badge and TLD[a] readings) are carefully kept for workers, but corresponding health records for workers are not kept and analysed nationally. In other countries, especially those with socialised medicine, excellent health records are kept but accurate radiation exposure records are neglected. Collection and analysis of radiation exposure records together with experience of ill health, including chronic long-term (non-fatal) problems, are required in order accurately to assess radiation-related health problems. Merely recording the first cause of death for workers is not sufficient.

  1. TLD -- thermoluminescent dosimeter, used to measure individual radiation doses of workers. It contains radiosensitive chips and must be carefully screened for the kind of radiation it is meant to detect. In a pilot study done in the US some processors of TLDs discovered that some of their chips were completely insensitive to the type of radiation for which they were purchased. See P. Plato and G. Hudson, `Performance Testing of Personnel Dosimetry Services: Alternatives and Recommendations for a Personnel Dosimetry Testing Program', US Nuclear Regulatory Commission (NUREG/CR-1593), 1980, p. 9.

The public is at an even greater disadvantage than the worker. There are no cumulative records of radiation exposures for individual members of the public from nuclear testing, military or commercial nuclear industries anywhere in the world. Because of this record-keeping vacuum, it is difficult, if not impossible, to challenge ICRP predictions.
Inadequate collection of information on public health by governments makes it difficult for scientists concerned about rising radiation exposure levels to document changes in public health. The problem is not that they are poor scientists, but that they do not have access to detailed information, since governments have failed to collect it. The health changes which can be detected, in spite of poor records, represent only a minute proportion of the undocumented whole.
One key to understanding what priority a country places on the health consequences of national defence and energy choices is the precision of its measurements of resultant health effects. Measurements of health effects can be made through controlled animal experiments or observation of the effects of unplanned human exposures. These measurements serve as an audit of human health effects or as an after-the-fact check on the accuracy of predictions. This technique of controlled observation is normally applied when a new drug or new medical procedure is introduced into general use. A prediction must prove its worth in real life.
As one would expect, predictive dose/response estimates for radiation exposure and specifically chosen severe health effects have been prolific in the USA. Not only has the USA maintained a tight control over and interest in research on the Japanese survivors of radiation exposure from the nuclear bombing of Hiroshima and Nagasaki, it also has a system of government-sponsored research laboratories controlled successively by the Atomic Energy Commission, the Energy Research and Development Administration and the Department of Energy. These bodies have been the source of almost all the original research papers published between 1945 and 1977 on the health effects of ionising radiation. Because radiation-related health effects are the result of the production, testing and use of atomic weapons, military goals and military secrecy have influenced both the selection of research questions and release of findings in the USA. The nuclear age is predicated on public acceptance of its consequences, hence `proving' that public acceptance is `rational' has a very high priority for government and industry-employed scientists. They have a vested interest in verifying the status quo.
Prior to the above-ground nuclear weapon test ban in 1963, the USA set off at least 183 atmospheric nuclear tests, more than all the other nations of the world combined. About half these tests were set off near the Pacific Trust Territory of Micronesia, given into US protection by the United Nations after the Second World War, and the other half were set off on the 1,350 square miles at the Nevada Test Site north of Las Vegas. By 1978 the USA had set off an additional 400 nuclear bombs below ground in Nevada, some of which were officially admitted to have `leaked' large amounts of radioactive chemicals. Some of the tests were of UK weapons since it also uses the Nevada test site. Underground tests are still taking place in the USA,[36] the USSR and French Polynesia. In the Northern Hemisphere, above-ground tests have also been detonated by the USSR, China and India and in the Southern Hemisphere by France and South Africa.
The Nevada nuclear tests have spread radiation poisons throughout central and eastern United States and Canada, and produced in the stratosphere a layer of radioactive material which encircles the globe. They also cause nitric oxides to form in the atmosphere which then descend on earth as acid rain. Radioactive chemicals can now be found in the organs, tissues and bones of every individual in the Northern Hemisphere, and the contamination from past nuclear explosions will continue to cause environmental and health problems for hundreds of thousands of years, even if all nuclear activities are stopped today. Siberian tests affect the north polar region.
Pollution of the Southern Hemisphere, though less than in the North, is progressing along the same path. Although the United States and Great Britain have ceased nuclear tests in the Pacific Ocean, France has not ceased them, and it appears that South Africa has begun to test. Brazil, Argentina and other nations are thought to be developing a nuclear weapon capability.
A 1977 report of the United Nations Scientific Committee on the Effects of Atomic Radiation stated that twenty atmospheric nuclear tests -- six in the Northern Hemisphere and fourteen in the Southern Hemisphere -- plus unnumbered underground tests, took place between 1972 and 1977. As a result of this nuclear testing radiation doses to the population increased by about 2 percent in the Northern Hemisphere, and 6 percent in the Southern Hemisphere over the dose estimated in 1970. The nuclear weapon testing carried out between 1972 and 1977 was insignificant when compared to that between 1945 and 1963.

This estimate does not include the dose from radioactive carbon (carbon 14) which, because of its 5730-year half-life, persists in the human food chain and has not yet taken its total human toll. For comparison purposes, 100 mrad is about equal to the amount of radiation a person receives from naturally occurring radiation in one year of chronological ageing. The dose commitment from nuclear weapon testing is spread over a fifty-year period, with most of the dose being delivered in the first year.
There has been no lack of victims of radiation pollution in the West to study both for refinement of predictions of biological harm and checks of adequacy of predictions relative to the real-life situation. Checking adequacy of predictions means including all hidden costs which must eventually be paid, including damage to agriculture and the biosphere. Government oversight should also include full disclosure of findings to the public as a test of the acceptability of such costs and as an evaluation of the judgments made for society by the nuclear experts.

The obvious answer is that we can, of course, find a way to measure gains and losses in health only the will to do so is lacking. In order to measure subtle changes in health a good reporting and recording system is needed, together with protection of privacy for the individual and ongoing biostatistical analysis of the accumulated data. Whole bodies of statistical theory, such as sequential analysis, used for product quality control, and system analysis, used to predict the outcome of a complicated interaction between interdependent variables, need to be used in the public health sector. This could provide a public health technology capable of managing military and industrial technology, able to act as a reality check on predictions and to give an early warning of dangers arising from within the big-system and threatening survival of the nation or, indeed, the human race. Biostatistical detection of problems needs to be followed by pathological, cytological and other confirmatory studies. No such serious systematic commitment to public health is evident relative to this nuclear issue anywhere in the world. Governments seem unaware that economic and military policies can be destructive of human health within the nation.
The radiation issue is further confused by statisticians and public health specialists who claim that there are some inherent and insurmountable problems which make it impossible to monitor the public health effects of pollution.[38] These professionals seem to limit themselves, consciously or unconsciously, to current inadequate data collection systems and mathematical tools. This is like deciding that it is impossible to travel to the moon on the basis that the only transportation possible is a commercial airliner. It will very probably require grass-roots scientific initiatives to cause governments to begin to act as strongly in protection of public health as they act to promote their own economic and military strategies.
Many people have become aware that national security strategies, especially nuclear weapon stockpiling, are increasing individual insecurity. Capital-intensive national economic strategies, designed to balance import/export dollar flow, can cause havoc with the individual citizen who is having to cope with the side effects of inflation and unemployment. Government neglect of health monitoring relative to economic and military strategies is, however, not yet perceived by the public as a serious problem.
It should be obvious that pollution of the environment with fission products will cause a wide variety of physiological changes in people exposed to them. There is little disagreement among scientists with regard to this conclusion.
There is also little controversy about the tragedy caused by uncontrolled fission -- whether deliberately or accidentally unleashed, whether from a nuclear reactor accident or an exploding warhead.
The question which causes controversy is: which health effects should be recognised as important for fiscal planning? `Important' may relate to public acceptance of the problem, or to the money which must be paid out for damage compensation, or the productive years lost through premature disability or death of workers. Once the significant health effects are identified, then quantification of these effects becomes the primary societal goal. This gives rise to scientific controversies. Present scientific controversy on low level radiation has to do with estimating the number of radiation-induced `excess cancer deaths' that are related to a given dose of ionising radiation. Fiscal concern has centered on radiation-induced excess cancers, and scientific concern on predicting this outcome.
These excess cancer numbers are important to planners who wish to show that their development schemes are less harmful than an alternative scheme. They are important to government officials who have to decide whether or not to assume the financial burden of ordering evacuation of a danger zone in a reactor accident like that at Three Mile Island. They are important to insurance companies, since they allow calculation of theoretical liability due to an accident. They are important to legislators who need to balance risks (deaths) against some military or economic benefit. They are important to strategic planners who calculate `collateral damage', i.e. the number of human deaths, after an atomic attack.
These numbers of specifically selected health effects, `radiation-induced excess cancer fatalities', predicted on the basis of the `average man's' reaction to a given average dose of ionising radiation, are of little meaningful use to individuals. Firstly, no one is really an `average man'. Also, populations may vary in the proportion of people with above-average susceptibility to radiation damage. Secondly, a `radiation-induced excess cancer fatality' is one of the least likely of the health problems to occur with exposure to low level radiation. More likely scenarios are radiation acceleration of a cancer caused by some other factor, such as cigarette smoking[b], earlier clinical expression of cancer, benign tumours, or related non-malignant health problems. Thirdly, even if the individual has a cancer it is almost impossible to present evidence to prove that his or her cancer is the excess one which would not have occurred without the radiation exposure. Therefore compensation for damage is almost impossible to obtain. Only one veteran from the USA exposed to radiation in its nuclear bomb programme has ever received compensation: Orvile Kelly. About six months before he died the Veterans Administration admitted that his illness could be attributed to radiation exposure. About 1,000 veteran claims have been refused.[39]

  1. Many researchers believe that the primary carcinogen in cigarettes is polonium 210, a radioactive daughter product of radon gas which is released from uranium mining and i mill tailings.

The usual `rational' approach to risk versus benefit planning by governments is irrational from the point of view of the individual. It undermines the individual's ability to control and understand his or her environment and to hold government accountable to its electorate.
The human body is delicately fashioned and the unique gifts of each person are meant to enrich the human family. Crude quantification of random damage to people which is used to justify political or military gains of the nation may be labelled sophisticated barbarianism. It is the decadent thinking of those who have accepted the rule of force and who envision a future earth ruled by a powerful country (the USA or the USSR) with a monopoly of weapons of mass destruction, able to terrorise all other nations into co-operating with some form of global economy and resource-sharing of their choosing.

A word needs to be said about health physics, a relatively new academic specialty which has emerged since the dropping of the atomic bomb. Systematic study of radiation health questions began at the University of Chicago when the first nuclear reactor began operating on 2 December 1942. Primarily under the leadership of physicists E. O. Wollan, H. M. Parker, C. C. Gamertsfelder, K. Z. Morgan, J. C. Hart, R. R. Coveyou, O. G. Landsverk and L. A. Pardue, it grew to become a recognised graduate-level discipline.[40]
While this was a much-needed specialty, its bias toward the so-called `hard sciences' -- physics, chemistry and engineering -- and neglect of the `soft sciences' -- biology, physiology and psychology -- has tended to create radiation safety officers rather than health professionals.
In a message from the President of the Health Physics Society published in the July 1971 issue of the Health Physics Journal,[41] Dade W. Moeller stated:

Membership of the Health Physics Society is broader than, but includes, licensed health physicists who have passed qualifying examinations. These latter are generally required to have a college degree with a major in physics, chemistry or engineering, and one year of graduate training in radiation measurement and safety practices.
Dade W. Moeller goes on to describe the members who had a college degree:

Even members of the Health Physics Society have complained about the pro-nuclear bias of its publication[42] but seldom has this been expressed as clearly as in this address by Dade Moeller. After reporting a need for 2,000 to 3,000 more health physicists by the year 2000 just to support the operation of nuclear power stations, he urged members to be active: `To paraphrase an old adage, "let's all put our mouth where our money is".'
Unfortunately, the Health Physics Society probably will not be in the vanguard speaking on behalf of workers and members of the public whose health is at risk from nuclear industries. The obvious and outstanding exception to this statement is Dr Karl Z. Morgan who has remained an open, honest and independent student of life. Dr Morgan has spoken out courageously on behalf of lowering worker and public exposures to radiation and avoiding all unnecessary exposures. In so doing he has alienated many of his peers and jeopardised his own research and teaching position. Karl Morgan was a friend of Hermann Müller and he remembers the geneticist's warning about undermining the health of a nation and its children.[43]
The United States, a leading nuclear nation, has failed to provide any reliable human health study either to confirm or to deny its prediction of the human health effects of exposure to chronic low level radiation, or even to provide a systematic health follow-up of the significant groups exposed to radiation so that there will in time be such a reliable study. The predictions of health effects are based primarily on the effects reported at Hiroshima and Nagasaki and the applicability of these estimates to chronic low dose exposure of a normal population has always been doubtful.[21]
The US government has also failed to supply the worker or the public with trained health professionals whose jobs are independent of the nuclear industry and whose training and background would enable them to alert people to a slowly deteriorating health situation. Adequate record-keeping and reporting would force public awareness of the problems, and probably the facing of ultimate questions such as: for what perceived benefit can society sacrifice the health of future generations?
The health physicist, while serving a necessary safety function within nuclear installations, does not fulfil the role of a health advocate in this situation. His or her job is to enforce regulations, not to question them and to support the nuclear plant management even if it is clear that the management is wrong.[44] This is not so much the result of malice as a normal outcome of believing `permissible' is the same as `safe', and trust that present regulations are `very safe'. It thus becomes acceptable to handle radioactive material and to cheat a little on over-exposures.
The first key to understanding governments' commitment to ensuring the survival of individual citizens is its adoption of a verification process for testing its prediction of severe health effects resulting from its economic and military strategies. In the United States, this leads to a preliminary judgment that individuals have been considered expendable. Health damage from radiation associated with military or economic ventures has not been easily traceable to the cause or immediately apparent to the public. No efforts deliberately to trace and make public all the health effects have been made. In fact, when any research has begun to show such effects, the researcher has been `discredited' and his or her funding discontinued.
On the basis of the US government's neglect of follow-up and record keeping on radiation-exposed people, and its lack of concern for mild genetic effects, the unrest of the US public with respect to further development of nuclear technology is highly rational. Continuance of present government neglect and unconcern is at best irrational and at worst genocidal. We may observe the same syndrome of irrational behaviour in other nuclear nations which are experiencing public unrest.
Although the problems inherent in the production of nuclear weapons and nuclear power reach a climax of scale in the United States, they are experienced in all countries with nuclear technology. Where one country may keep excellent public health records, it has poor records of individual radiation exposures. Where another keeps detailed radiation exposure histories, it has no detailed medical history. As long as part of the information is missing, the worker and general public are forced to rely on predictions made by `recognised experts' which are not verified by factual studies. This is really a forecast with no audit allowed. The promotion of nuclear technology in developing nations as the industry loses support in the developed world is even more disturbing.
Before moving on, some of the concepts of radiation protection important for nuclear workers, the general public and medical personnel need to be emphasised. First, an assurance of `no immediate danger' with respect to exposure to ionising radiation is empty when it masks long-term effects resulting from incorporation of radiochemicals in sensitive tissues and/or the results of biological magnification of cell damage or radiation-induced genetic mistakes. Secondly, independent testing of urine, faeces, exhalation, tissues removed in surgery, baby teeth and hair for radioactivity, must become routine laboratory tests for medical diagnostic purposes as we try to cope with the fission product pollution already in the biosphere. Thirdly, when assessing the impact of any leak, abnormal release, normal effluence or waste which is radioactive, it is essential to know the radiochemicals involved: their physical and biological properties, the potential pathways to human beings and the length of time they remain toxic. Fourthly, the health effects of radiation differ with the age of the person exposed, his or her physical status and prior experience.
The second key to governmental priorities in decision-making is found in the historical context of the nuclear development. This is examined later. First we must try to understand the practices of nuclear technology in the military and civil sectors.


Stochastic means random in nature. There is a statistical accounting for all diseases that could be caused by any of several different xenobiotics or carcinogens any random occurrence of a disease that cannot be attributed solely to radiation is stochastic. As far as cancer is concerned, it is extremely difficult to say whether a particular cancer is attributable to a specific exposure because most cancers have a 20-y latency period from exposure to manifestation. Therefore, chronic low-dose radiation exposure effects are seen as stochastic. At diagnostic levels, where doses are low, stochastic effects are random and the odds of having any effect are extremely low. A few people may experience an effect from the radiation exposure, but this cannot be predicted. Radiation risks from diagnostic imaging are considered to be stochastic. Also, heredity effects and carcinogenesis are considered to be stochastic (5).

Ionizing radiation at high doses causes certain specific effects. Therefore, at certain doses, certain predictable outcomes can be determined. These are called nonstochastic, or deterministic, effects. These effects are very predictable and range from blood and chromosome aberrations to radiation sickness to certain death, depending on the dose, dose rate, age, immune capacity of an individual, and type of radiation exposure.

For γ- and x-ray radiation, exposure measured in grays and sieverts (rads and rems) is equal however, this is not true of neutron radiation or when the quality factor is greater than 1 for the conversion between rads and rems. Nonstochastic (deterministic) effects include hematologic syndrome (pancytopenia), erythema, gastrointestinal syndrome (radiation sickness), and central nervous system syndrome (Table 2).

Summary of Nonstochastic (Deterministic) Effects (5)

One concept used to gauge toxicity is that of the lethal dose to 50% of the population (LD50) exposed to the agent observed at a specific time. The LD50 at 30 d (LD50/30) for humans due to ionizing radiation exposure is approximately 2.5–4.5 Gy (250–450 rad). This estimate for humans varies between different sources and is primarily empiric. Therefore, concrete data are not available. In other organisms, the LD50/30 factor has been established through experiments (Table 3) (5).

LD50/30 Values for Different Species (5)

258 Biological Effects of Ionizing Radiation

We hear many seemingly contradictory things about the biological effects of ionizing radiation. It can cause cancer, burns, and hair loss, yet it is used to treat and even cure cancer. How do we understand these effects? Once again, there is an underlying simplicity in nature, even in complicated biological organisms. All the effects of ionizing radiation on biological tissue can be understood by knowing that ionizing radiation affects molecules within cells, particularly DNA molecules.

Let us take a brief look at molecules within cells and how cells operate. Cells have long, double-helical DNA molecules containing chemical codes called genetic codes that govern the function and processes undertaken by the cell. It is for unraveling the double-helical structure of DNA that James Watson, Francis Crick, and Maurice Wilkins received the Nobel Prize. Damage to DNA consists of breaks in chemical bonds or other changes in the structural features of the DNA chain, leading to changes in the genetic code. In human cells, we can have as many as a million individual instances of damage to DNA per cell per day. It is remarkable that DNA contains codes that check whether the DNA is damaged or can repair itself. It is like an auto check and repair mechanism. This repair ability of DNA is vital for maintaining the integrity of the genetic code and for the normal functioning of the entire organism. It should be constantly active and needs to respond rapidly. The rate of DNA repair depends on various factors such as the cell type and age of the cell. A cell with a damaged ability to repair DNA, which could have been induced by ionizing radiation, can do one of the following:

  • The cell can go into an irreversible state of dormancy, known as senescence.
  • The cell can commit suicide, known as programmed cell death.
  • The cell can go into unregulated cell division leading to tumors and cancers.

Since ionizing radiation damages the DNA, which is critical in cell reproduction, it has its greatest effect on cells that rapidly reproduce, including most types of cancer. Thus, cancer cells are more sensitive to radiation than normal cells and can be killed by it easily. Cancer is characterized by a malfunction of cell reproduction, and can also be caused by ionizing radiation. Without contradiction, ionizing radiation can be both a cure and a cause.

To discuss quantitatively the biological effects of ionizing radiation, we need a radiation dose unit that is directly related to those effects. All effects of radiation are assumed to be directly proportional to the amount of ionization produced in the biological organism. The amount of ionization is in turn proportional to the amount of deposited energy. Therefore, we define a radiation dose unit called the rad , as of a joule of ionizing energy deposited per kilogram of tissue, which is

For example, if a 50.0-kg person is exposed to ionizing radiation over her entire body and she absorbs 1.00 J, then her whole-body radiation dose is

If the same 1.00 J of ionizing energy were absorbed in her 2.00-kg forearm alone, then the dose to the forearm would be

and the unaffected tissue would have a zero rad dose. While calculating radiation doses, you divide the energy absorbed by the mass of affected tissue. You must specify the affected region, such as the whole body or forearm in addition to giving the numerical dose in rads. The SI unit for radiation dose is the gray (Gy) , which is defined to be

However, the rad is still commonly used. Although the energy per kilogram in 1 rad is small, it has significant effects since the energy causes ionization. The energy needed for a single ionization is a few eV, or less than . Thus, 0.01 J of ionizing energy can create a huge number of ion pairs and have an effect at the cellular level.

The effects of ionizing radiation may be directly proportional to the dose in rads, but they also depend on the type of radiation and the type of tissue. That is, for a given dose in rads, the effects depend on whether the radiation is x-ray, or some other type of ionizing radiation. In the earlier discussion of the range of ionizing radiation, it was noted that energy is deposited in a series of ionizations and not in a single interaction. Each ion pair or ionization requires a certain amount of energy, so that the number of ion pairs is directly proportional to the amount of the deposited ionizing energy. But, if the range of the radiation is small, as it is for s, then the ionization and the damage created is more concentrated and harder for the organism to repair, as seen in (Figure). Concentrated damage is more difficult for biological organisms to repair than damage that is spread out, so short-range particles have greater biological effects. The relative biological effectiveness (RBE) or quality factor (QF) is given in (Figure) for several types of ionizing radiation—the effect of the radiation is directly proportional to the RBE. A dose unit more closely related to effects in biological tissue is called the roentgen equivalent man or rem and is defined to be the dose in rads multiplied by the relative biological effectiveness.

The image shows ionization created in cells by and radiation. Because of its shorter range, the ionization and damage created by is more concentrated and harder for the organism to repair. Thus, the RBE for s is greater than the RBE for s, even though they create the same amount of ionization at the same energy.

So, if a person had a whole-body dose of 2.00 rad of radiation, the dose in rem would be . If the person had a whole-body dose of 2.00 rad of radiation, then the dose in rem would be . The s would have 20 times the effect on the person than the s for the same deposited energy. The SI equivalent of the rem is the sievert (Sv), defined to be , so that

The RBEs given in (Figure) are approximate, but they yield certain insights. For example, the eyes are more sensitive to radiation, because the cells of the lens do not repair themselves. Neutrons cause more damage than rays, although both are neutral and have large ranges, because neutrons often cause secondary radiation when they are captured. Note that the RBEs are 1 for higher-energy s, s, and x-rays, three of the most common types of radiation. For those types of radiation, the numerical values of the dose in rem and rad are identical. For example, 1 rad of radiation is also 1 rem. For that reason, rads are still widely quoted rather than rem. (Figure) summarizes the units that are used for radiation.

“Activity” refers to the radioactive source while “dose” refers to the amount of energy from the radiation that is deposited in a person or object.

A high level of activity doesn’t mean much if a person is far away from the source. The activity of a source depends upon the quantity of material (kg) as well as the half-life. A short half-life will produce many more disintegrations per second. Recall that . Also, the activity decreases exponentially, which is seen in the equation .

Relative Biological Effectiveness
Type and energy of radiation RBE 1
X-rays 1
rays 1
rays greater than 32 keV 1
rays less than 32 keV 1.7
Neutrons, thermal to slow (<20 keV) 2–5
Neutrons, fast (1–10 MeV) 10 (body), 32 (eyes)
Protons (1–10 MeV) 10 (body), 32 (eyes)
rays from radioactive decay 10–20
Heavy ions from accelerators 10–20
Units for Radiation
Quantity SI unit name Definition Former unit Conversion
Activity Becquerel (bq) decay/s Curie (Ci)
Absorbed dose Gray (Gy) 1 J/kg rad
Dose Equivalent Sievert (Sv) 1 J/kg × RBE rem

The large-scale effects of radiation on humans can be divided into two categories: immediate effects and long-term effects. (Figure) gives the immediate effects of whole-body exposures received in less than one day. If the radiation exposure is spread out over more time, greater doses are needed to cause the effects listed. This is due to the body’s ability to partially repair the damage. Any dose less than 100 mSv (10 rem) is called a low dose , 0.1 Sv to 1 Sv (10 to 100 rem) is called a moderate dose , and anything greater than 1 Sv (100 rem) is called a high dose . There is no known way to determine after the fact if a person has been exposed to less than 10 mSv.

Immediate Effects of Radiation (Adults, Whole Body, Single Exposure)
Dose in Sv 2 Effect
0–0.10 No observable effect.
0.1 – 1 Slight to moderate decrease in white blood cell counts.
0.5 Temporary sterility 0.35 for women, 0.50 for men.
1 – 2 Significant reduction in blood cell counts, brief nausea and vomiting. Rarely fatal.
2 – 5 Nausea, vomiting, hair loss, severe blood damage, hemorrhage, fatalities.
4.5 LD50/32. Lethal to 50% of the population within 32 days after exposure if not treated.
5 – 20 Worst effects due to malfunction of small intestine and blood systems. Limited survival.
>20 Fatal within hours due to collapse of central nervous system.

Immediate effects are explained by the effects of radiation on cells and the sensitivity of rapidly reproducing cells to radiation. The first clue that a person has been exposed to radiation is a change in blood count, which is not surprising since blood cells are the most rapidly reproducing cells in the body. At higher doses, nausea and hair loss are observed, which may be due to interference with cell reproduction. Cells in the lining of the digestive system also rapidly reproduce, and their destruction causes nausea. When the growth of hair cells slows, the hair follicles become thin and break off. High doses cause significant cell death in all systems, but the lowest doses that cause fatalities do so by weakening the immune system through the loss of white blood cells.

The two known long-term effects of radiation are cancer and genetic defects. Both are directly attributable to the interference of radiation with cell reproduction. For high doses of radiation, the risk of cancer is reasonably well known from studies of exposed groups. Hiroshima and Nagasaki survivors and a smaller number of people exposed by their occupation, such as radium dial painters, have been fully documented. Chernobyl victims will be studied for many decades, with some data already available. For example, a significant increase in childhood thyroid cancer has been observed. The risk of a radiation-induced cancer for low and moderate doses is generally assumed to be proportional to the risk known for high doses. Under this assumption, any dose of radiation, no matter how small, involves a risk to human health. This is called the linear hypothesis and it may be prudent, but it is controversial. There is some evidence that, unlike the immediate effects of radiation, the long-term effects are cumulative and there is little self-repair. This is analogous to the risk of skin cancer from UV exposure, which is known to be cumulative.

There is a latency period for the onset of radiation-induced cancer of about 2 years for leukemia and 15 years for most other forms. The person is at risk for at least 30 years after the latency period. Omitting many details, the overall risk of a radiation-induced cancer death per year per rem of exposure is about 10 in a million, which can be written as .

If a person receives a dose of 1 rem, his risk each year of dying from radiation-induced cancer is 10 in a million and that risk continues for about 30 years. The lifetime risk is thus 300 in a million, or 0.03 percent. Since about 20 percent of all worldwide deaths are from cancer, the increase due to a 1 rem exposure is impossible to detect demographically. But 100 rem (1 Sv), which was the dose received by the average Hiroshima and Nagasaki survivor, causes a 3 percent risk, which can be observed in the presence of a 20 percent normal or natural incidence rate.

The incidence of genetic defects induced by radiation is about one-third that of cancer deaths, but is much more poorly known. The lifetime risk of a genetic defect due to a 1 rem exposure is about 100 in a million or , but the normal incidence is 60,000 in a million. Evidence of such a small increase, tragic as it is, is nearly impossible to obtain. For example, there is no evidence of increased genetic defects among the offspring of Hiroshima and Nagasaki survivors. Animal studies do not seem to correlate well with effects on humans and are not very helpful. For both cancer and genetic defects, the approach to safety has been to use the linear hypothesis, which is likely to be an overestimate of the risks of low doses. Certain researchers even claim that low doses are beneficial. Hormesis is a term used to describe generally favorable biological responses to low exposures of toxins or radiation. Such low levels may help certain repair mechanisms to develop or enable cells to adapt to the effects of the low exposures. Positive effects may occur at low doses that could be a problem at high doses.

Even the linear hypothesis estimates of the risks are relatively small, and the average person is not exposed to large amounts of radiation. (Figure) lists average annual background radiation doses from natural and artificial sources for Australia, the United States, Germany, and world-wide averages. Cosmic rays are partially shielded by the atmosphere, and the dose depends upon altitude and latitude, but the average is about 0.40 mSv/y. A good example of the variation of cosmic radiation dose with altitude comes from the airline industry. Monitored personnel show an average of 2 mSv/y. A 12-hour flight might give you an exposure of 0.02 to 0.03 mSv.

Doses from the Earth itself are mainly due to the isotopes of uranium, thorium, and potassium, and vary greatly by location. Some places have great natural concentrations of uranium and thorium, yielding doses ten times as high as the average value. Internal doses come from foods and liquids that we ingest. Fertilizers containing phosphates have potassium and uranium. So we are all a little radioactive. Carbon-14 has about 66 Bq/kg radioactivity whereas fertilizers may have more than 3000 Bq/kg radioactivity. Medical and dental diagnostic exposures are mostly from x-rays. It should be noted that x-ray doses tend to be localized and are becoming much smaller with improved techniques. (Figure) shows typical doses received during various diagnostic x-ray examinations. Note the large dose from a CT scan. While CT scans only account for less than 20 percent of the x-ray procedures done today, they account for about 50 percent of the annual dose received.

Radon is usually more pronounced underground and in buildings with low air exchange with the outside world. Almost all soil contains some and , but radon is lower in mainly sedimentary soils and higher in granite soils. Thus, the exposure to the public can vary greatly, even within short distances. Radon can diffuse from the soil into homes, especially basements. The estimated exposure for is controversial. Recent studies indicate there is more radon in homes than had been realized, and it is speculated that radon may be responsible for 20 percent of lung cancers, being particularly hazardous to those who also smoke. Many countries have introduced limits on allowable radon concentrations in indoor air, often requiring the measurement of radon concentrations in a house prior to its sale. Ironically, it could be argued that the higher levels of radon exposure and their geographic variability, taken with the lack of demographic evidence of any effects, means that low-level radiation is less dangerous than previously thought.

Radiation Protection

Laws regulate radiation doses to which people can be exposed. The greatest occupational whole-body dose that is allowed depends upon the country and is about 20 to 50 mSv/y and is rarely reached by medical and nuclear power workers. Higher doses are allowed for the hands. Much lower doses are permitted for the reproductive organs and the fetuses of pregnant women. Inadvertent doses to the public are limited to of occupational doses, except for those caused by nuclear power, which cannot legally expose the public to more than of the occupational limit or 0.05 mSv/y (5 mrem/y). This has been exceeded in the United States only at the time of the Three Mile Island (TMI) accident in 1979. Chernobyl is another story. Extensive monitoring with a variety of radiation detectors is performed to assure radiation safety. Increased ventilation in uranium mines has lowered the dose there to about 1 mSv/y.

Background Radiation Sources and Average Doses
Source Dose (mSv/y) 3
Source Australia Germany United States World
Natural Radiation – external
Cosmic Rays 0.30 0.28 0.30 0.39
Soil, building materials 0.40 0.40 0.30 0.48
Radon gas 0.90 1.1 2.0 1.2
Natural Radiation – internal
0.24 0.28 0.40 0.29
Medical & Dental 0.80 0.90 0.53 0.40
TOTAL 2.6 3.0 3.5 2.8

To physically limit radiation doses, we use shielding , increase the distance from a source, and limit the time of exposure.

(Figure) illustrates how these are used to protect both the patient and the dental technician when an x-ray is taken. Shielding absorbs radiation and can be provided by any material, including sufficient air. The greater the distance from the source, the more the radiation spreads out. The less time a person is exposed to a given source, the smaller is the dose received by the person. Doses from most medical diagnostics have decreased in recent years due to faster films that require less exposure time.

Typical Doses Received During Diagnostic X-ray Exams
Procedure Effective dose (mSv)
Chest 0.02
Dental 0.01
Skull 0.07
Leg 0.02
Mammogram 0.40
Barium enema 7.0
Upper GI 3.0
CT head 2.0
CT abdomen 10.0

Problem-Solving Strategy

You need to follow certain steps for dose calculations, which are

Step 1.Examine the situation to determine that a person is exposed to ionizing radiation.

Step 2.Identify exactly what needs to be determined in the problem (identify the unknowns). The most straightforward problems ask for a dose calculation.

Step 3.Make a list of what is given or can be inferred from the problem as stated (identify the knowns). Look for information on the type of radiation, the energy per event, the activity, and the mass of tissue affected.

Step 4.For dose calculations, you need to determine the energy deposited. This may take one or more steps, depending on the given information.

Step 5.Divide the deposited energy by the mass of the affected tissue. Use units of joules for energy and kilograms for mass. If a dose in Sv is involved, use the definition that .

Step 6.If a dose in mSv is involved, determine the RBE (QF) of the radiation. Recall that .

Step 7.Check the answer to see if it is reasonable: Does it make sense? The dose should be consistent with the numbers given in the text for diagnostic, occupational, and therapeutic exposures.

Calculate the dose in rem/y for the lungs of a weapons plant employee who inhales and retains an activity of in an accident. The mass of affected lung tissue is 2.00 kg, the plutonium decays by emission of a 5.23-MeV particle, and you may assume the higher value of the RBE for s from (Figure).

Dose in rem is defined by and . The energy deposited is divided by the mass of tissue affected and then multiplied by the RBE. The latter two quantities are given, and so the main task in this example will be to find the energy deposited in one year. Since the activity of the source is given, we can calculate the number of decays, multiply by the energy per decay, and convert MeV to joules to get the total energy.

The activity decays/s. So, the number of decays per year is obtained by multiplying by the number of seconds in a year:

Thus, the ionizing energy deposited per year is

Dividing by the mass of the affected tissue gives

One Gray is 1.00 J/kg, and so the dose in Gy is

First note that the dose is given to two digits, because the RBE is (at best) known only to two digits. By any standard, this yearly radiation dose is high and will have a devastating effect on the health of the worker. Worse yet, plutonium has a long radioactive half-life and is not readily eliminated by the body, and so it will remain in the lungs. Being an emitter makes the effects 10 to 20 times worse than the same ionization produced by s, rays, or x-rays. An activity of is created by only of (left as an end-of-chapter problem to verify), partly justifying claims that plutonium is the most toxic substance known. Its actual hazard depends on how likely it is to be spread out among a large population and then ingested. The Chernobyl disaster’s deadly legacy, for example, has nothing to do with the plutonium it put into the environment.

Risk versus Benefit

Medical doses of radiation are also limited. Diagnostic doses are generally low and have further lowered with improved techniques and faster films. With the possible exception of routine dental x-rays, radiation is used diagnostically only when needed so that the low risk is justified by the benefit of the diagnosis. Chest x-rays give the lowest doses—about 0.1 mSv to the tissue affected, with less than 5 percent scattering into tissues that are not directly imaged. Other x-ray procedures range upward to about 10 mSv in a CT scan, and about 5 mSv (0.5 rem) per dental x-ray, again both only affecting the tissue imaged. Medical images with radiopharmaceuticals give doses ranging from 1 to 5 mSv, usually localized. One exception is the thyroid scan using . Because of its relatively long half-life, it exposes the thyroid to about 0.75 Sv. The isotope is more difficult to produce, but its short half-life limits thyroid exposure to about 15 mSv.

Watch alpha particles escape from a polonium nucleus, causing radioactive alpha decay. See how random decay times relate to the half life. Click to open media in new browser.

Section Summary

  • The biological effects of ionizing radiation are due to two effects it has on cells: interference with cell reproduction, and destruction of cell function.
  • A radiation dose unit called the rad is defined in terms of the ionizing energy deposited per kilogram of tissue:

Conceptual Questions

Isotopes that emit radiation are relatively safe outside the body and exceptionally hazardous inside. Yet those that emit radiation are hazardous outside and inside. Explain why.

Why is radon more closely associated with inducing lung cancer than other types of cancer?

The RBE for low-energy />s is 1.7, whereas that for higher-energy />s is only 1. Explain why, considering how the range of radiation depends on its energy.

Which methods of radiation protection were used in the device shown in the first photo in (Figure)? Which were used in the situation shown in the second photo?

What radioisotope could be a problem in homes built of cinder blocks made from uranium mine tailings? (This is true of homes and schools in certain regions near uranium mines.)

Are some types of cancer more sensitive to radiation than others? If so, what makes them more sensitive?

Suppose a person swallows some radioactive material by accident. What information is needed to be able to assess possible damage?

Problems & Exercises

What is the dose in mSv for: (a) a 0.1 Gy x-ray? (b) 2.5 mGy of neutron exposure to the eye? (c) 1.5 mGy of exposure?

Find the radiation dose in Gy for: (a) A 10-mSv fluoroscopic x-ray series. (b) 50 mSv of skin exposure by an emitter. (c) 160 mSv of and rays from the in your body.

How many Gy of exposure is needed to give a cancerous tumor a dose of 40 Sv if it is exposed to activity?

What is the dose in Sv in a cancer treatment that exposes the patient to 200 Gy of rays?

One half the rays from are absorbed by a 0.170-mm-thick lead shielding. Half of the rays that pass through the first layer of lead are absorbed in a second layer of equal thickness. What thickness of lead will absorb all but one in 1000 of these rays?

A plumber at a nuclear power plant receives a whole-body dose of 30 mSv in 15 minutes while repairing a crucial valve. Find the radiation-induced yearly risk of death from cancer and the chance of genetic defect from this maximum allowable exposure.

In the 1980s, the term picowave was used to describe food irradiation in order to overcome public resistance by playing on the well-known safety of microwave radiation. Find the energy in MeV of a photon having a wavelength of a picometer.

Find the mass of that has an activity of .


    Values approximate, difficult to determine. Multiply by 100 to obtain dose in rem. Multiply by 100 to obtain dose in mrem/y.


gray (Gy) the SI unit for radiation dose which is defined to be linear hypothesis assumption that risk is directly proportional to risk from high doses rad the ionizing energy deposited per kilogram of tissue sievert the SI equivalent of the rem relative biological effectiveness (RBE) a number that expresses the relative amount of damage that a fixed amount of ionizing radiation of a given type can inflict on biological tissues quality factor same as relative biological effectiveness roentgen equivalent man (rem) a dose unit more closely related to effects in biological tissue low dose a dose less than 100 mSv (10 rem) moderate dose a dose from 0.1 Sv to 1 Sv (10 to 100 rem) high dose a dose greater than 1 Sv (100 rem) hormesis a term used to describe generally favorable biological responses to low exposures of toxins or radiation shielding a technique to limit radiation exposure

Plight of the bumblebee

Using a radiation facility at the University of Stirling, we studied the effect of dose rates typically seen in the CEZ on commercial bumblebee colonies that were exposed for a month.

We chose bumblebees for several reasons: first, these insects are essential pollinators so any effects may have consequences for the ecosystem second, there are studies on the impact of pesticides showing how bumblebees respond to stress and third, bumblebees are used within the International System for Radiological Protection (ICRP) which sets guidelines for every country to adhere to. However, at the moment there is little data on how bees respond to chronic radiation exposure.

We found that exposure to dose rates comparable to the CEZ resulted in a reduction in the number of queens produced from colonies – with upper estimates of a 30-45% reduction compared with unexposed colonies. Queens are important because bumblebees are annual, socially organised insects, which means that colonies only live for one year and only the queen reproduces with help from the workers for food collection and colony maintenance. The queens from the previous year will hibernate over winter and start a new colony in the spring.

The health of bumblebee populations is used as an indicator within the International System for Radiological Protection. Shutterstock

The queen starts a new colony and produces workers until the end of summer when she changes to either male or new queen production. Afterwards, the colony dies and the new queens hibernate again.

New queens are significantly larger than males and are considered to be more resource intensive to produce. The more queens produced, the more bumblebees nests there will be the following year. A reduction in queen production is a common response to stress and has been shown in exposure to insecticides.

We also showed that bumblebee colonies grew more slowly when exposed to radiation, reaching peak weight a week later than unexposed colonies. The study did not find an effect on colony weight or how long the colony or individual bees lived. The relationship between dose rate and effects was not linear, which would indicate a proportional increase in radiation would directly result in a decrease in queen production. Instead, the relationship was a curve showing a more significant proportionate response occurred at lower radiation levels.


Epidemiological Studies

One of the first places that we find supporting evidence for radiation hormesis is in the data on atomic bomb survivors. Figure 3 shows leukemia incidence as a function of radiation dose. Note that the data points actually decrease below the natural incidence of leukemia in the low-dose range. Many scientists have tried to write off this part of the graph as a statistical artifact, but it certainly resembles the proposed hormetic effect of radiation illustrated in Figure 2.

Incidence of leukemia as function of radiation dose in atomic bomb survivors in Japan. (Reprinted with permission of (3).)

Two studies have looked at death rates in areas of high natural background radiation. One study in China compared an area with average radiation exposure of 2.31 mSv/y (231 mrem/y) with a similar area with only 0.96 mSv/y (96 mrem/y) average exposure (9). The cancer mortality rate was lower in the high-background group, but this difference was statistically significant only in the 40- to 70-y age group (i.e., those who had the greatest lifelong exposure to high background levels of radiation). A study in India showed an inverse correlation between background radiation levels and cancer incidence and mortality (10).

Because there is less attenuation of cosmic radiation at high altitudes, a region at high altitude can be studied as a high-background area. One such study used 2 regions: a low-altitude region (<300 m [1,000 ft] 825,000 inhabitants) and a high-altitude region (>900 m [3,000 ft] 350,000 inhabitants) (11). The cancer death rate was lower in the high-altitude group. This study was controlled for industrialization, urbanization, and ethnicity but not for smoking or diet, which may limit its value.

Two studies have considered the effect of occupational radiation exposure among nuclear industry workers. One in Canada found that nuclear industry workers had cancer mortality that was 58% of the national average (12). In the same study, nonnuclear power industry workers had cancer mortality equal to 97% of the national average, thus discrediting in this case the “healthy worker effect” that often is a problem in epidemiology. Matanoski et al. (13) reported on 700,000 U.S. shipyard workers, including 108,000 nuclear shipyard workers. The 29,000 nuclear shipyard workers with the highest cumulative doses (>5 mSv) had a 24% lower death rate (from all causes) than 33,000 nonnuclear workers, a group with a death rate equal to that of the general population.

The study that caught the attention of the health physics community was published by Bernard Cohen of the University of Pittsburgh (14). Cohen studied the relationship between home radon levels and lung cancer rates, with the idea that he could prove or disprove the LNT hypothesis at low radiation doses. Radon is a daughter in the 238 U decay chain. Because its natural state is gaseous, it can be inhaled into the lungs. If it decays there, it becomes a heavy metal that becomes stuck in the airways and emits α-particles. Thus, increased home radon levels are expected to result in an increased incidence of lung cancer. Cohen deliberately chose this study because it fits the population averaging used by the LNT paradigm: in large populations exposed to low but measurable amounts of radon, an increase in cancer rates should be detectable.

Cohen’s study compared lung cancer death rates with radon levels in 1,600 counties in the United States. He found that the death rate from lung cancer decreased 7% for each additional 0.027 Bq/L (pCi/L) of radon in the air. No one believed this at first, including Cohen. He reanalyzed his data to correct for migration patterns, smoking, and 54 other socioeconomic variables. He continued to find a negative relationship between radon levels and lung cancer death rates.

Cohen’s study was highly controversial in the health physics community, because it so completely contradicted the LNT paradigm. A major criticism of the study was that it assumed that average exposure determines average risk, whereas most epidemiological studies relate individual exposures to individual risks. Cohen’s response was that the tenets of the LNT paradigm allow population averaging and, therefore, his study design should be a valid test of the hypothesis. The results of Cohen’s analysis continue to spark discussion and debate.

Experimental Studies

In addition to epidemiological studies, we should also examine experimental data before we endorse the idea of radiation hormesis. Actual experimental evidence of the repair of radiation damage has been available since 1960, when Elkind and Sutton-Gilbert (15) demonstrated the phenomenon of sublethal damage and its repair. A lethal dose of radiation, when split into 2 portions and separated by 2 h or more, produces much less cell killing than the same dose administered at one time.

More recent studies have sought to demonstrate a hormetic effect of radiation. In one experiment, lymphocytes irradiated with 1.5 Gy (150 rad) demonstrated 30%–40% chromosome breakage. When preirradiated with 0.01–0.03 Gy (1–3 rad), followed by 1.5 Gy (150 rad), the chromosome breakage dropped to 15%–20% (16). Another study demonstrated not only a decrease in mutations when cells were preirradiated compared with nonpreirradiated cells, but also showed that the kinds of mutations in preirradiated cells were qualitatively different than in cells not preirradiated (17). A third study showed that a single low dose of radiation (0.001 Gy [0.1 rad]) reduced the probability that a cell would undergo neoplastic transformation (18).

Radiation exposure can be shown to activate cellular protection and repair mechanisms. Feinendegen et al. (19) demonstrated that the glutathione levels in cells increase for about 5 h after a radiation exposure. In the same time period, DNA synthesis is inhibited. Early enzymatic repair of DNA damage is roughly doubled in cells irradiated with 0.25 Gy (25 rad) followed by 2 Gy (200 rad) compared with cells irradiated only with 2 Gy (20).

Low levels of radiation exposure have also been shown to have a stimulatory effect on the immune system. Hashimoto et al. (21) implanted tumors in the leg muscles of rats. The rats were then treated in 3 groups: total-body irradiation, local irradiation of the implant site, and no radiation (control). Those rats receiving 2 Gy (200 rad) total-body irradiation demonstrated fewer metastases, more CD8+ T-lymphocytes in the spleen, and more lymphocytes infiltrating the tumor compared with the local irradiation and control groups. Neither radiation regimen had any effect on the growth rate of the implanted tumor itself.

Several other lines of evidence demonstrate the hormetic effect of radiation. The survivors of the atomic bombs at Hiroshima and Nagasaki, as a group, are living longer than a control group (5). In the 1940s and 1950s, Lorenz and colleagues exposed mice and guinea pigs to 110 mR/d until their natural deaths. The exposed animals had longer life spans by 2%–14% and 50% greater body weight than unexposed controls (22).

A small amount of radiation risk is involved in the nuclear stress test. This can be minimised by exposing the individual to a basic standardised protocol and performing additional detailed testing only if needed.

The closest alternative and non radiation alternative test is a Stress Echocardiography Test. In this investigation the heart functioning is studied using an ultrasound machine. Stress echocardiography results might vary with the skill of the person conducting the test and operator variability exists. Nuclear stress on the other hand is not much operator dependent and the results are more comprehensive.

Another alternative to nuclear stress test is a CT Coronary Angiography. This uses radiation and is done after injecting intravenous contrast medium and then taking pictures of the blood vessels in the coronary circulation. This is also a non operator dependent test.

Watch the video: 3 Ways to Express Your Thoughts So That Everyone Will Understand You. Alan Alda. Big Think (July 2022).


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