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Fear of Radiation – Is it rational?

Executive Summary

Fear of RadiationRadiation is all around us. We are continually exposed to natural background radiation, which seems to be without any problem. Yes, high doses of ionizing radiation are harmful and potentially lethal to living beings, but these doses must be high. Moreover, what is not harmful in high doses? Even a high amount of water can be lethal to living beings.

The truth about low-dose radiation health effects still needs to be found. It is unknown whether these low doses of radiation are detrimental or beneficial (and where is the threshold). Some studies claim that small doses of radiation given at a low dose rate stimulate the defense mechanisms. Moreover, ionizing radiation can have health benefits in medicine, for example, in diagnostics, where X-rays are used to produce pictures of the inside of the body. We do not claim that everything is OK, and it also depends on the type of radiation and tissue which was exposed.

But finally, if you compare risks, which arise from the existence of the radiation, natural or artificial, with risks, which arise from everyday life, then you must conclude that fear of radiation is irrational. Humans are often inconsistent in our treatment of perceived risks. Even though two situations may have similar risks, people will find one situation permissible and another unjustifiably dangerous.

The problem of ionizing radiation lies in the fact that the radiation is invisible and not directly detectable by human senses. People can neither see nor feel radiation, and therefore, they feel fear of this invisible threat.

ionizing radiation - hazard symbol
Ionizing radiation – hazard symbol

How Dangerous is Radiation

Radiation is all around us. In, around, and above the world we live in. It is a natural energy force that surrounds us, and it is a part of our natural world that has been here since the birth of our planet. From the beginning of time, all living creatures have been, and are still being, exposed to ionizing radiation.

For example, potassium-40 is one of the isotopes contributing to humans’ internal exposure. Traces of potassium-40 are found in all potassium, the most common radioisotope in the human body. Higher amounts can also be found in bananas. Does it mean eating bananas must be dangerous? Of course not.

Explanation - Banana Equivalent Dose

In all cases, the intensity of radiation matters. Banana equivalent dose is intended as a general educational example to compare a dose of radioactivity to the dose one is exposed to by eating one average-sized banana. One BED is often correlated to 10-7 Sievert (0.1 µSv). The radiation exposure from consuming a banana is approximately 1% of the average daily exposure to radiation, which is 100 banana equivalent doses (BED). A chest CT scan delivers 58,000 BED (5.8 mSv). A lethal dose, which kills a human with a 50% risk within 30 days (LD50/30) of radiation, is approximately 50,000,000 BED (5000 mSv). However, this dose is not cumulative in practice, as the principal radioactive component is excreted to maintain metabolic equilibrium. Moreover, there is also a problem with the collective dose.

The BED is only meant to inform the public about the existence of very low levels of natural radioactivity within a natural food. It is not a formally adopted dose measurement.

Whether the source of radiation is natural or artificial, whether it is a large dose of radiation or a small dose, there will be some biological effects. In general, ionizing radiation is harmful and potentially lethal to living beings. Still, it can have health benefits in medicine, for example, in radiation therapy for treating cancer and thyrotoxicosis.

But where is the threshold between positive and negative effects of radiation?””
What does danger mean?””

In the following thoughts, we try to summarize facts and hypotheses which can help you understand the problem. It is all about the risks from exposure to ionizing radiation and the consistency in all risks of everyday life. But first, we have to summarize key facts about ionizing radiation.

The intensity of Radiation – Dose and Dose Rate

radiation protection pronciples - time, distance, shielding
Principles of Radiation Protection – Time, Distance, Shielding

The intensity of ionizing radiation is a key factor determining the health effects of exposure to radiation. It is similar to being exposed to heat radiation from a fire (in fact, it is also transferred by photons). If you are too close to a fire, the intensity of thermal radiation is high, and you can get burned. If you are at the right distance, you can withstand it without any problems, and it is comfortable. If you are too far from a heat source, the insufficiency of heat can also hurt you. In a certain sense, this analogy can be applied to radiation from ionizing radiation sources.

In short, to get burned (deterministic effects and demonstrable stochastic effects) by ionizing radiation, you must be exposed to a high amount of radiation. But almost every time, we are talking about so-called low doses. As written today, the protection system is based on the LNT hypothesis, a conservative model used in radiation protection to estimate the health effects of small radiation doses. This model is excellent for setting up a protection system for all use of ionizing radiation. This model assumes that there is no threshold point and risk increases linearly with a dose, i.e., the LNT model implies that there is no safe dose of ionizing radiation. If this linear model is correct, natural background radiation is the most hazardous radiation source to general public health, followed by medical imaging as a close second. It must be added that the research during the last two decades is very interesting and show that small doses of radiation given at a low dose rate stimulate the defense mechanisms. Therefore the LNT model is not universally accepted, with some proposing an adaptive dose-response relationship where low doses are protective, and high doses are detrimental. Many studies have contradicted the LNT model and shown an adaptive response to low dose radiation resulting in reduced mutations and cancers. On the other hand, it is very important to know what type of radiation a person is exposed to.

Natural Background Radiation

Natural and Artificial Radiation SourcesNatural background radiation is ionizing radiation that originates from various natural sources. From the beginning of time, all living creatures have been, and are still being, exposed to ionizing radiation. This radiation is not associated with any human activity. Radioactive isotopes exist in our bodies, houses, air, water, and soil. We all are also exposed to radiation from outer space.

Sources of Natural Background Radiation

We divide all these natural radiation sources into three groups:

LNT Model and Hormesis Model
Alternative assumptions for the extrapolation of the cancer risk vs. radiation dose to low-dose levels, given a known risk at a high dose: LNT model and hormesis model.

You can not go through life without radiation. The danger of ionizing radiation lies in the fact that the radiation is invisible and not directly detectable by human senses. People can neither see nor feel radiation, yet it deposits energy into the body’s molecules.

But don’t worry. The doses from background radiation are usually very small (except for radon exposure). A low dose means additional small doses comparable to the normal background radiation (10 µSv = average daily dose received from natural background). The problem is that, at very low doses, it is practically impossible to correlate any irradiation with certain biological effects. This is because the baseline cancer rate is already very high, and the risk of developing cancer fluctuates by 40% because of individual lifestyle and environmental effects, obscuring the subtle effects of low-level radiation.

Intensity - Acute and Chronic Doses

The biological effects of radiation and their consequences depend strongly on the level of dose rate obtained. Dose rate is a measure of radiation dose intensity (or strength). Low-level doses are common in everyday life. In the following points, a few examples of radiation exposure can be obtained from various sources.

  • 05 µSv – Sleeping next to someone
  • 09 µSv – Living within 30 miles of a nuclear power plant for a year
  • 1 µSv – Eating one banana
  • 3 µSv – Living within 50 miles of a coal power plant for a year
  • 10 µSv – Average daily dose received from natural background
  • 20 µSv – Chest X-ray

It is very important to distinguish between doses received over short and extended periods from biological consequences. Therefore, the biological effects of radiation are typically divided into two categories.

  • Acute Doses. An “acute dose” (short-term high-level dose) occurs over a short and finite period, i.e., within a day.
  • Chronic Doses. A “chronic dose” (long-term low-level dose) is a dose that continues for an extended period, i.e., weeks and months so that it is better described by a dose rate.

High doses tend to kill cells, while low doses tend to damage or change them. High doses can cause visually dramatic radiation burns and/or rapid fatality through acute radiation syndrome. Acute doses below 250 mGy are unlikely to have any observable effects. Acute doses of about 3 to 5 Gy have a 50% chance of killing a person some weeks after the exposure if a person receives no medical treatment.

Low doses spread out over long periods don’t cause an immediate problem to any body organ. The effects of low doses of radiation occur at the level of the cell, and the results may not be observed for many years. Moreover, some studies demonstrate that most human tissues exhibit a more pronounced tolerance to the effects of low-LET radiation in case of a prolonged exposure compared to a one-time exposure to a similar dose.

See also: Lethal Dose

Deterministic and Stochastic Effects

In radiation protection, most adverse health effects of radiation exposure are usually divided into two broad classes:

  • Deterministic effects are threshold health effects related directly to the absorbed radiation dose, and the severity of the effect increases as the dose increases.
  • Stochastic effects occur by chance, generally occurring without a threshold dose level. The probability of occurrence of stochastic effects is proportional to the dose, but the effect’s severity is independent of the dose received.

Deterministic Effects

Deterministic effects (or non-stochastic health effects) are health effects that are related directly to the absorbed radiation dose, and the severity of the effect increases as the dose increases. Deterministic effects have a threshold below which no detectable clinical effects do occur. The threshold may be very low (of the order of magnitude of 0.1 Gy or higher) and may vary from person to person. For doses between 0.25 Gy and 0.5 Gy, slight blood changes may be detected by medical evaluations, and for doses between 0.5 Gy and 1.5 Gy, blood changes will be noted. Symptoms of nausea, fatigue, and vomiting occur.

Once the threshold has been exceeded, the severity of an effect increases with the dose. This threshold dose is because radiation damage (serious malfunction or death) of a critical population of cells (high doses tend to kill cells) in a given tissue needs to be sustained before an injury is expressed in a clinically relevant form. Therefore, deterministic effects are also termed tissue reactions. They are also called non-stochastic effects to contrast with chance-like stochastic effects (e.g., cancer induction).

Deterministic effects are not necessarily more or less serious than stochastic effects. High doses can cause visually dramatic radiation burns and/or rapid fatality through acute radiation syndrome. Acute doses below 250 mGy are unlikely to have any observable effects. Acute doses of about 3 to 5 Gy have a 50% chance of killing a person some weeks after the exposure if a person receives no medical treatment. Deterministic effects can ultimately lead to a temporary nuisance or fatality. Examples of deterministic effects:

Examples of deterministic effects are:

  • Acute radiation syndrome, by acute whole-body radiation
  • Radiation burns, from radiation to a particular body surface
  • Radiation-induced thyroiditis, a potential side effect of radiation treatment against hyperthyroidism
  • Chronic radiation syndrome from long-term radiation.
  • Radiation-induced lung injury, from, for example, radiation therapy to the lungs

Stochastic Effects

Stochastic effects of ionizing radiation occur by chance, generally occurring without a threshold level of dose. The probability of occurrence of stochastic effects is proportional to the dose, but the effect’s severity is independent of the dose received. The biological effects of radiation on people can be grouped into somatic and hereditary effects. Somatic effects are those suffered by the exposed person, and hereditary effects are those suffered by the offspring of the individual exposed. Cancer risk is usually mentioned as the main stochastic effect of ionizing radiation, but also hereditary disorders are stochastic effects.

According to ICRP:

(83) On the basis of these calculations, the Commission proposes nominal probability coefficients for detriment-adjusted cancer risk as 5.5 x 10-2 Sv-1 for the whole population and 4.1 x 10-2 Sv-1 for adult workers. For heritable effects, the detriment-adjusted nominal risk in the whole population is estimated as 0.2 x 10-2 Sv-1 and in adult workers as 0.1 x 10-2 Sv-1.

Special Reference: ICRP, 2007. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann. ICRP 37 (2-4).

The SI unit for effective dose, the sievert, represents the equivalent biological effect of depositing a joule of gamma rays energy in a kilogram of human tissue. As a result, one sievert represents a 5.5% chance of developing cancer. Note that the effective dose is not intended as a measure of deterministic health effects, which is the severity of acute tissue damage that is certain to happen, measured by the quantity absorbed dose.

Biological Effects and Dose Limits

In radiation protection, dose limits are set to limit stochastic effects to an acceptable level and to prevent deterministic effects completely. Note that stochastic effects arise from chance: the greater the dose, the more likely the effect. Deterministic effects normally have a threshold: above this, the severity of the effect increases with the dose. Dose limits are a fundamental component of radiation protection, and breaching these limits is against radiation regulation in most countries. Note that the dose limits described in this article apply to routine operations. They do not apply to an emergency situation when human life is endangered. They do not apply in emergency exposure situations where an individual attempts to prevent a catastrophic situation.

The limits are split into two groups, the public and occupationally exposed workers. According to ICRP, occupational exposure refers to all exposure incurred by workers in the course of their work, except for

  1. excluded exposures and exposures from exempt activities involving radiation or exempt sources
  2. any medical exposure
  3. the normal local natural background radiation.

The following table summarizes dose limits for occupationally exposed workers and the public:

dose limits - radiation
Table of dose limits for occupationally exposed workers and the public.
Source of data: ICRP, 2007. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann. ICRP 37 (2-4).

Source of data: ICRP, 2007. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann. ICRP 37 (2-4).

According to the recommendation of the ICRP in its statement on tissue reactions of 21. April 2011, the equivalent dose limit for the eye lens for occupational exposure in planned exposure situations was reduced from 150 mSv/year to 20 mSv/year, averaged over defined periods of 5 years, with no annual dose in a single year exceeding 50 mSv.

Limits on effective dose are for the sum of the relevant, effective doses from external exposure in the specified period and the committed effective dose from intakes of radionuclides in the same period. For adults, the committed effective dose is computed for 50 years after intake, whereas for children, it is computed for the period up to 70 years. The effective whole-body dose limit of 20 mSv is an average value over five years, and the real limit is 100 mSv in 5 years, with not more than 50 mSv in any year.

Controversy of LNT Model

As was written previously (LNT model), today, the protection system is based on the LNT hypothesis, a conservative model used in radiation protection to estimate the health effects of small radiation doses. This model is excellent for setting up a protection system for all use of ionizing radiation. Compared to the hormesis model, the LNT model assumes that there is no threshold point and risk increases linearly with a dose, i.e., the LNT model implies that there is no safe dose of ionizing radiation. If this linear model is correct, natural background radiation is the most hazardous radiation source to general public health, followed by medical imaging as a close second.

The LNT model is primarily based on Japan’s life span study (LSS) of atomic bomb survivors. However, while this pattern is undisputed at high doses, this linear extrapolation of risk to low doses is challenged by many recent experiments involving cell mechanisms. There is also high uncertainty involved in estimating risk using only epidemiological studies. The problem is that, at very low doses, it is practically impossible to correlate any irradiation with certain biological effects. This is because the baseline cancer rate is already very high, and the risk of developing cancer fluctuates by 40% because of individual lifestyle and environmental effects, obscuring the subtle effects of low-level radiation. Government and regulatory bodies assume an LNT model instead of a threshold or hormesis not because it is the more scientifically convincing but because it is, the more conservative estimate.

In the case of low doses, its conservativeness (linearity) has enormous consequences. The model is sometimes wrongly (perhaps intentionally) used to quantify the cancerous effect of collective doses of low-level radioactive contamination. A linear dose-effect curve makes it possible to use collective doses to calculate the detrimental effects on an irradiated population. It is also argued that the LNT model had caused an irrational fear of radiation since every microsievert can be converted to the probability of cancer induction, however small this probability is. For example, if ten million people receive an effective dose of 0.1 µSv (the equivalent of eating one banana), then the collective dose will be S = 1 Sv. Does it mean there is a 5.5% chance of developing cancer for one person due to eating bananas? Note that, for high doses, one sievert represents a 5.5% chance of developing cancer.

The problem with this model is that it neglects many defense biological processes that may be crucial at low doses. The research during the last two decades is very interesting and shows that small doses of radiation at a low dose rate stimulate the defense mechanisms. Therefore the LNT model is not universally accepted, with some proposing an adaptive dose-response relationship where low doses are protective, and high doses are detrimental. Many studies have contradicted the LNT model and shown an adaptive response to low dose radiation resulting in reduced mutations and cancers.

Type of Radiation – High-LET x Low-LET

Radiation weighting factors - current - ICRP
Source: ICRP Publ. 103: The 2007 Recommendations of the International Commission on Radiological Protection

This section is about the fact that there are several types of ionizing radiation, and each type of radiation interacts with matter differently. When discussing the radiation intensity, we must consider which type of radiation we are exposed to. For example, alpha radiation tends to travel only a short distance and does not penetrate very far into a tissue, if at all. Therefore, alpha radiation is sometimes treated as non-hazardous since it cannot penetrate the surface layers of human skin. This is naturally true, but this is not valid for internal exposure to alpha radionuclides. When inhaled or ingested, alpha radiation is much more dangerous than other types of radiation. Note that the radiation weighting factor for alpha radiation is equal to 20. Biological effects of any radiation increase with the linear energy transfer (LET) were discovered. In short, the biological damage from high-LET radiation (alpha particles, protons, or neutrons) is much greater than that from low-LET radiation (gamma rays).

Shielding of Ionizing RadiationIonizing radiation is categorized by the nature of the particles or electromagnetic waves that create the ionizing effect. These particles/waves have different ionization mechanisms and may be grouped as:

  • Directly ionizing. Charged particles (atomic nuclei, electrons, positrons, protons, muons, etc.) can ionize atoms directly by fundamental interaction through the Coulomb force if it carries sufficient kinetic energy. These particles must move at relativistic speeds to reach the required kinetic energy. Even photons (gamma rays and X-rays) can ionize atoms directly (despite they are electrically neutral) through the Photoelectric effect and the Compton effect, but secondary (indirect) ionization is much more significant.
  • Indirectly ionizing. Indirect ionizing radiation is electrically neutral particles and therefore does not interact strongly with matter. The bulk of the ionization effects is due to secondary ionizations.

External x Internal Exposure

As was written, it is crucial whether we are exposed to radiation from external or internal sources. This is similar to other dangerous substances. Internal exposure is more dangerous than external exposure since we carry the radiation source inside our bodies, and we cannot use any of the radiation protection principles (time, distance, shielding). The intake of radioactive material can occur through various pathways such as ingesting radioactive contamination in food or liquids, inhalation of radioactive gases, or through intact or wounded skin. In this place, we have to distinguish between radiation and contamination. Radioactive contamination consists of radioactive material that generates ionizing radiation. It is the source of radiation, not radiation itself. Anytime radioactive material is not in a sealed radioactive source container and might be spread onto other objects, radioactive contamination is possible. For example, radioiodine, iodine-131, is an important radioisotope of iodine. Radioiodine plays a major role as a radioactive isotope present in nuclear fission products. It is a major contributor to health hazards when released into the atmosphere during an accident. Iodine-131 has a half-life of 8.02 days. The target tissue for radioiodine exposure is the thyroid gland. The external beta and gamma dose from radioiodine present in the air is quite negligible compared to the committed dose to the thyroid resulting from breathing this air.

Internal Dose Uptake

If the radiation source is inside our body, we say it is internal exposure. The intake of radioactive material can occur through various pathways such as ingesting radioactive contamination in food or liquids, inhalation of radioactive gases, or through intact or wounded skin. Most radionuclides will give you much more radiation dose if they can somehow enter your body than they would if they remained outside. For internal doses, we first should distinguish between intake and uptake. Intake means what a person takes in, and uptake means what a person keeps.

When a radioactive compound enters the body, the activity will decrease with time due both to radioactive decay and biological clearance. The decrease varies from one radioactive compound to another. For this purpose, the biological half-life is defined in radiation protection.

The biological half-life is the time taken for the amount of a particular element in the body to decrease to half of its initial value due to elimination by biological processes alone when the removal rate is roughly exponential. The biological half-life depends on the rate at which the body normally uses a particular compound of an element. Radioactive isotopes that were ingested or taken in through other pathways will gradually be removed from the body via bowels, kidneys, respiration, and perspiration. This means that a radioactive substance can be expelled before it has had the chance to decay.

As a result, the biological half-life significantly influences the effective half-life and the overall dose from internal contamination. If a radioactive compound with a radioactive half-life (t1/2) is cleared from the body with a biological half-life tb, the effective half-life (te) is given by the expression:

As can be seen, the biological mechanisms always decrease the overall dose from internal contamination. Moreover, if t1/2 is large compared to tb, the effective half-life is approximately the same as tb.

For example, tritium has a biological half-life of about 10 days, while the radioactive half-life is about 12 years. On the other hand, radionuclides with very short radioactive half-lives also have very short effective half-lives. These radionuclides will deliver, for all practical purposes, the total radiation dose within the first few days or weeks after intake.

For tritium, the annual limit intake (ALI) is 1 x 109 Bq. Taking 1 x 109 Bq of tritium will receive a whole-body dose of 20 mSv. The committed effective dose, E(t), is 20 mSv. It does not depend on whether a person intakes this amount of activity in a short or long time. In every case, this person gets the same whole-body dose of 20 mSv.

Contamination versus Radiation

Radioactive contamination consists of radioactive material that generates ionizing radiation and is the source of radiation, not radiation itself. Anytime radioactive material is not in a sealed radioactive source container and might be spread onto other objects, radioactive contamination is possible. Radioactive contamination may be characterized by the following points:

  • Radioactive contamination consists of radioactive material (contaminants) that may be solid, liquid, or gaseous. Large contaminants can be visible, but you cannot see radiation produced.
  • When released, contaminants can be spread by air, water, or mechanical contact.
  • We cannot shield against contamination.
  • We can mitigate contamination by protecting the integrity of barriers (source container, fuel cladding, reactor vesselcontainment building)
  • Since contaminants interact chemically, they may be contained within objects such as the human body.
  • We can eliminate contamination by many mechanical, chemical (decontaminate surfaces), or biological processes (biological half-life).
  • It is of the highest importance which material is the radioactive contaminant (half-life, mode of decay, energy).

Ionizing radiation is formed by high-energy particles (photonselectrons, etc.) that can penetrate matter and ionize (to form ions by losing electrons) target atoms to form ions. Radiation exposure is the consequence of the presence nearby the source of radiation. Radiation exposure as a quantity is defined as a measure of the ionization of material due to ionizing radiation. The danger of ionizing radiation lies in the fact that the radiation is invisible and not directly detectable by human senses. People can neither see nor feel radiation, yet it deposits energy into the molecules of the body. The energy is transferred in small quantities for each interaction between radiation and a molecule, and there are usually many such interactions. Unlike radioactive contamination, radiation may be characterized by the following points:

  • Radiation consists of high-energy particles that can penetrate matter and ionize (to form ions by losing electrons) target atoms. Radiation is invisible and not directly detectable by human senses. It must be noted that beta radiation is indirectly visible due to Cherenkov radiation.
  • Unlike contamination, radiation cannot be spread by any medium. It travels through materials until it loses its energy. We can shield radiation (e.g., by standing around the corner).
  • Exposure to ionizing does not necessarily mean that the object becomes radioactive (except for very rare neutron radiation).
  • Radiation can penetrate barriers, but a sufficiently thick barrier can minimize all effects.
  • Unlike contaminants, radiation cannot interact chemically with matter and cannot be bound inside the body.
  • It is not important which material is the source of certain radiation. The only type of radiation and energy matters.
Airborne Contamination

Airborne contamination is particularly important in nuclear power plants, which must be monitored. Contaminants can become airborne, especially during reactor top head removal, reactor refueling, and during manipulations within the spent fuel pool. The air can be contaminated with radioactive isotopes, especially particulate form, which poses a particular inhalation hazard. This contamination consists of various fission and activation products that enter the air in gaseous, vapor, or particulate form. There are four types of airborne contamination in nuclear power plants, namely:

  • Particulates. Particulate activity is an internal hazard because it can be inhaled. Transportable particulate material taken into the respiratory system will enter the bloodstream and be carried to all parts of the body. Non-transportable particulates will stay in the lungs with a certain biological half-life. For example, Sr-90, Ra-226, and Pu-239 are radionuclides known as bone-seeking radionuclides. These radionuclides have long biological half-lives and are serious internal hazards. Once deposited in bone, they remain unchanged in amount during the individual’s lifetime. The continued action of the emitted alpha particles can cause significant injury. Over many years, they deposit all their energy in a tiny volume of tissue because the range of the alpha particles is very short.
  • Noble gases. Radioactive noble gases, such as xenon-133, xenon-135, and  krypton-85, are present in reactor coolant, especially when fuel leakages are present. As they appear in coolant, they become airborne, and they can be inhaled and exhaled right after inhaling because the body does not react chemically with them. If workers work in a noble gas cloud, their external dose is about 1000 times greater than the internal dose. Because of this, we are only concerned about the external beta and gamma dose rates.
  • Iodine 131 - decay schemeRadioiodine. Radioiodineiodine-131, is an important radioisotope of iodine. Radioiodine plays a major role as a radioactive isotope present in nuclear fission products. It is a major contributor to health hazards when released into the atmosphere during an accident. Iodine-131 has a half-life of 8.02 days. The target tissue for radioiodine exposure is the thyroid gland. The external beta and gamma dose from radioiodine present in the air is quite negligible compared to the committed dose to the thyroid resulting from breathing this air. The biological half-life for iodine inside the human body is about 80 days (according to ICRP). Iodine in food is absorbed by the body and preferentially concentrated in the thyroid, where it is needed for the functioning of that gland. When 131I is present in high levels in the environment from radioactive fallout, it can be absorbed through contaminated food and accumulate in the thyroid. 131I decays with a half-life of 8.02 days with beta particle and gamma emissions. As it decays, it may cause damage to the thyroid. The primary risk from exposure to high levels of 131I is the chance of radiogenic thyroid cancer in later life. For 131I, ICRP has calculated that if you inhale 1 x 106 Bq, you will receive a thyroid dose of HT = 400 mSv (and a weighted whole-body dose of 20 mSv).
  • Tritium. Tritium is a byproduct of nuclear reactors. The most important source (due to releases of tritiated water) of tritium in nuclear power plants stems from the boric acid, commonly used as a chemical shim to compensate for an excess of initial reactivity. Note that tritium emits low-energy beta particles with a short range in body tissues and, therefore, poses a risk to health as a result of internal exposure only following ingestion in drinking water or food, or inhalation or absorption through the skin. The tritium taken into the body is uniformly distributed among all soft tissues. According to the ICRP, a biological half-time of tritium is 10 days for HTO and 40 days for OBT (organically bound tritium) formed from HTO in the body of adults. As a result, for an intake of 1 x 109 Bq of tritium (HTO), an individual will get a whole-body dose of 20 mSv (equal to the intake of 1 x 106 Bq of 131I). While for PWRs, tritium poses a minor risk to health, for heavy water reactors, it contributes significantly to a collective dose of plant workers. Note that “Air saturated with moderator water at 35°C can give 3 000 mSv/h of tritium to an unprotected worker (See also: J.U.Burnham. Radiation Protection). The best protection from tritium can be achieved using an air-supplied respirator. Tritium cartridge respirators protect workers only by a factor of 3. The only way to reduce skin absorption is by wearing plastics. In PHWR power plants, workers must wear plastics for work in atmospheres containing more than 500 μSv/h.

Consistency in all Risks

Finally, it is all about the risks of exposure to ionizing radiation and the consistency in all risks of everyday life. In general, danger (also risk or peril) is the possibility of something bad happening. A situation with a risk of something bad happening is called dangerous, risky, or perilous. Yes, ionizing radiation sounds very dangerous, but how exactly dangerous is radiation?

Humans are often inconsistent in our treatment of perceived risks. Even though two situations may have similar risks, people will find one situation permissible and another unjustifiably dangerous. For radiation risks, doses to the public must be kept under 1 mSv/year. Even for the very conservative case of linear no-threshold assumption, one millisievert represents a 0.0055% chance of some detrimental health effects. Two points:

  • In our opinion, this is an acceptable risk. On average, annual doses from natural background radiation are about 3.7 mSv/year (10 µSv = average daily dose received from natural background).
  • Moreover, the problem with this model is that it neglects many defense biological processes that may be crucial at low doses. The research during the last two decades is very interesting and shows that small doses of radiation at a low dose rate stimulate the defense mechanisms.

Annually received dose of 1 mSv causes very conservatively about 0.0055% chance of some detrimental health effects. In April 2012, a year after the Fukushima accident, cleanup efforts were supposed to be happening wherever the radiation dose exceeded government regulations. Entire towns are still off limits because the annual dose from the ground is projected to be greater than 50 mSv or even 20 mSv, leaving many people in the area homeless and jobless. But did anyone take into account the health effects of this evacuation. The consequences of low-level radiation are often more psychological than radiological. Forced evacuation from a radiological or nuclear accident may lead to social isolation, anxiety, depression, psychosomatic medical problems, reckless behavior, and even suicide. Such was the outcome of the 1986 Chernobyl nuclear disaster in Ukraine. A comprehensive 2005 study concluded that “the mental health impact of Chernobyl is the largest public health problem unleashed by accident to date.” But what if the threshold model is true, and doses of up to 100 mSv/yr result in no detectable health risks? This would mean that people are being unnecessarily kept away and prevented from working on their farms for negligible health effects. Recall that the annual dose in some parts of Araxa, Brazil is higher than 20 mSv. In contrast, the average dose examined in the three-country nuclear worker studies was 30-40 mSv/yr. These studies found no significant increase in solid cancers or leukemias from those doses.

Another point of view can be obtained when we consider all everyday life risks. What about risks that arise from transportation. Nearly 1.25 million people die in road crashes each year, on average 3,287 deaths a day. Road crashes are the leading cause of death among young people ages 15-29 and the second leading cause of death worldwide among young people ages 5-14. On the road, people don’t realize the kinetic energy of a car. So why do we not stop driving cars? Yes, transportation is today essential, but so are the peaceful uses of radiation. And what about smoking cigarettes? Cigarettes also contain polonium-210, originating from the decay products of radon, which stick to tobacco leaves. Polonium-210 emits a 5.3 MeV alpha particle, which provides most of the equivalent dose. Heavy smoking results in a dose of 160 mSv/year to localized spots at the bifurcations of segmental bronchi in the lungs from the decay of polonium-210. This dose is not readily comparable to the radiation protection limits since the latter deal with whole body doses. In contrast, the dose from smoking is delivered to a very small portion of the body.

Finally, we would like to discuss a very interesting fact. It is generally known that the increasing use of nuclear power and electricity generation using nuclear reactors will lead to a small but increasing radiation dose to the general public. But it is not generally known that power generation from coal also creates additional exposures, and, what is more interesting. In contrast, exposure levels are very low, and the coal cycle contributes more than half of the total radiation dose to the global population from electricity generation. The nuclear fuel cycle contributes less than one-fifth of this. The collective dose, which is defined as the sum of all individual effective doses in a group of people over the period or during the operation being considered due to ionizing radiation, is:

  • 670-1400 man Sv for coal cycle, depending on the age of the power plant,
  • 130 man Sv for nuclear fuel cycle,
  • 5-160 man Sv for geothermal power,
  • 55 man Sv for natural gas
  • 03 man Sv for oil

Yes, these results should be seen from the perspective of the share of each technology in worldwide electricity production. Since 40 percent of the world’s energy was produced by the coal cycle in 2010 and 13 percent by nuclear, the normalized collective dose will be about the same:

  • 7 – 1.4 man Sv/GW.a (man sievert per gigawatt year) for coal cycle
  • 43 man Sv/GW.a (man sievert per gigawatt year) for nuclear fuel cycle

Special Reference: Sources and effects of ionizing radiation, UNSCEAR 2016 – Annex B. New York, 2017. ISBN: 978-92-1-142316-7.

See also: Radiation Exposures from Electricity Generation

References:

Radiation Protection:

  1. Knoll, Glenn F., Radiation Detection and Measurement 4th Edition, Wiley, 8/2010. ISBN-13: 978-0470131480.
  2. Stabin, Michael G., Radiation Protection, and Dosimetry: An Introduction to Health Physics, Springer, 10/2010. ISBN-13: 978-1441923912.
  3. Martin, James E., Physics for Radiation Protection 3rd Edition, Wiley-VCH, 4/2013. ISBN-13: 978-3527411764.
  4. U.S.NRC, NUCLEAR REACTOR CONCEPTS
  5. U.S. Department of Energy, Instrumentation, and Control. DOE Fundamentals Handbook, Volume 2 of 2. June 1992.

Nuclear and Reactor Physics:

  1. J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
  2. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
  3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
  4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
  5. W.S.C. Williams. Nuclear and Particle Physics. Clarendon Press; 1 edition, 1991, ISBN: 978-0198520467
  6. G.R.Keepin. Physics of Nuclear Kinetics. Addison-Wesley Pub. Co; 1st edition, 1965
  7. Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.
  8. U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
  9. Paul Reuss, Neutron Physics. EDP Sciences, 2008. ISBN: 978-2759800414.

See above:

Radiation Protection