Nick Connor

Radiation is all around us. In, around, and above the world we live in. It is a natural energy force that surrounds us. It is a part of our natural world that has been here since the birth of our planet. All living creatures, from the beginning of time, have been, and are still being, exposed to ionizing radiation. Ionizing radiation is generated through nuclear reactions, nuclear decay, by very high temperature, or via acceleration of charged particles in electromagnetic fields.

Radiation Exposures from Coal Cycle

The public is also exposed to radiation from so called “enhanced sources of naturally occurring radioactive material”. This means also industries such as metal mining, coal mining and power production from coal creates additional exposures due to densification of naturally occurring radionuclides. Coal is the predominant source of energy used to produce electricity today. Coal cycle is a process chain consisting of a series of differing stages. For the coal cycle, the life cycle includes:

• coal mining,
• power plant operation,
• coal ash deposits.

According to the UNSCEAR, power generation from coal and entire coal cycle contribute more than half of the total radiation dose to the global population from electricity generation. This statement will seem paradoxical to many readers, since it’s not commonly known that non-nuclear energy sources release any radiation into the environment. But power generation from coal also creates additional exposures to public. Even nuclear fuel cycle releases less radiation into the environment than coal cycle and any other major energy source.

The problem is coal itself and especially coal ash (fly ash). Coal, a combustible black or brownish-black sedimentary rock, contains a substantial amount of the radioactive elements uranium and thorium. According to the UNSCEAR, the average specific activity of both uranium-238 and thorium-232 in coal is generally around 20 Bq/kg (range 5-300 Bq/kg). Coal mines in Freital, Germany, which have uranium concentrations of 15000 Bq/kg coal, are an exception. Burning coal gasifies its organic materials, concentrating its inorganic components into the remaining waste, called fly ash. Around 10% of coal is fly ash. Fly ash is hazardous and toxic to human beings and some other living things, and fly ash also contains the radioactive elements uranium and thorium, which are concentrated by a factor of 10. It must be emphasized, even fly ash does not possess any health hazards to the public. There are a few restrictions on the use of fly ash in landfill and road construction. Most restrictions are on the use in building construction, where it can result in increased exposures especially from radon. In any case, we don’t want to cause any irrational fear of radiation from coal. It does not mean, that it must be dangerous. In case of radiation from electricity generation, the doses are usually very, very low. Moreover, these results cannot be used to determine whether one form of energy generation is preferable to another.

The collective dose, which results from coal cycle is:

• 670-1400 man Sv for coal cycle, depending on the age of the power plant,

When considering the amount of electricity generated in the year 2010 by each technology, the coal cycle resulted in the largest collective dose to the global public and workers combined, followed by the nuclear fuel cycle. Of the remaining technologies, geothermal energy and combustion of natural gas were the next largest contributors.

The normalized collective dose (per gigawatt and year) is:

• 0.7 – 1.4 man Sv/GW.a (man sievert per gigawatt year) for coal cycle

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

In the following points we try to express ranges of radiation exposure from electricity generation together with doses from, which 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

The above doses are related to public exposure. If we consider occupational exposure, regarding the coal mining and fly ash deposits, the collective dose is higher especially for coal miners. Coal miners as a group receive the largest collective dose of radiation, through enhanced exposure to naturally occurring radionuclides.

Note that, the collective effective dose is often used to estimate the total health effects, but according to the ICRP this should be avoided (see more: Collective Dose).

See also:

Electricity Generation

In radiation therapy, the aim of the treatment is to deliver a very high dose to the tumour, but as little dose as possible to the surrounding healthy tissue. In this case, we are not talking about low doses. Using beams of high-energy gamma rays from cobalt-60 or from accelerators, localized high dose of radiation is delivered to tumour and this radiation tend to kill tumour cells. The amount of radiation used in photon radiation therapy is measured in grays (Gy), and varies depending on the type and stage of cancer being treated.

For curative cases, the typical dose for a solid epithelial tumor ranges from 60 to 80 Gy (locally), while lymphomas are treated with 20 to 40 Gy. Note that, this is not the effective dose. A gray is unit of absorbed dose, which is defined as the amount of energy deposited by ionizing radiation in a tumour.

See also:

Medical Exposures

Nuclear medicine is a medical science that involves the application of radioactive substances for diagnostic and treatment purposes. Nuclear medicine uses a very small amounts of radioactive materials called radiotracers, which are taken internally, for example, intravenously or orally. Then, external detectors (gamma cameras) capture and form images from the radiation emitted by the radiotracers. Sometimes the radioactive drug can be used in the treatment itself: an example is the treatment of thyroid disease with I-131. Nuclear medicine imaging is unlike a diagnostic X-ray, where external radiation is passed through the body to form an image. It also provides unique information that often cannot be obtained using other imaging procedures.

Average effective dose for most nuclear medicine procedures varies between 0.3 and 20 mSv. The common bone scan with 600 MBq of technetium-99m has an effective dose of approximately 3.5 mSv. These doses can be compared with the average annual effective dose from background radiation of about 3 mSv.

In the following points we try to express enormous ranges of radiation exposure as well as a few doses from medical sources.

• 1 µSv – Eating one banana
• 1 µSv – Extremity (hand, foot, etc.) X-ray
• 5 µSv – Dental X-ray
• 10 µSv – Average daily dose received from natural background
• 40 µSv – A 5-hour airplane flight
• 100 µSv – Chest X-ray
• 600 µSv – mammogram
• 1 000 µSv – Dose limit for individual members of the public, total effective dose per annum
• 3 650 µSv – Average yearly dose received from natural background
• 5 800 µSv – Chest CT scan
• 10 000 µSv – Average yearly dose received from natural background in Ramsar, Iran
• 20 000 µSv – single full-body CT scan
• 80 000 µSv – The annual local dose to localized spots at the bifurcations of segmental bronchi in the lungs caused by smoking cigarettes (1.5 packs/day).
• 175 000 µSv – Annual dose from natural radiation on a monazite beach near Guarapari, Brazil.
• 5 000 000 µSv – Dose that kills a human with a 50% risk within 30 days (LD50/30), if the dose is received over a very short duration.

As can be seen, low-level doses are common for everyday life.

See also:

Medical Exposures

Diagnostic X-rays use a very small dose of ionizing radiation to produce pictures of the inside of the body. Diagnostic X-ray exams account for about 90% of the radiation dose the population receives from medical sources. Chest X-rays (about 100 µSv) are the most common and they account for about 25% of all X-ray exams, followed by X-rays of the shoulder, pelvis and limbs (another 25%) and dental X-rays (10%). Note that, there is no direct evidence of radiation ever causing any harm at the exposure levels encountered with diagnostic radiological examinations.

X-rays belong to so called low-LET radiation. It was discovered, biological effects of any radiation increases with the linear energy transfer (LET). 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, X-rays). This is because the living tissue can more easily repair damage from radiation that is spread over a large area than that which is concentrated in a small area. Of course, at very high levels of exposure X-rays can still cause a great deal of damage to tissues.

In the following points we try to express enormous ranges of radiation exposure as well as a few doses from medical sources.

• 1 µSv – Eating one banana
• 1 µSv – Extremity (hand, foot, etc.) X-ray
• 5 µSv – Dental X-ray
• 10 µSv – Average daily dose received from natural background
• 40 µSv – A 5-hour airplane flight
• 100 µSv – Chest X-ray
• 600 µSv – mammogram
• 1 000 µSv – Dose limit for individual members of the public, total effective dose per annum
• 3 650 µSv – Average yearly dose received from natural background
• 5 800 µSv – Chest CT scan
• 10 000 µSv – Average yearly dose received from natural background in Ramsar, Iran
• 20 000 µSv – single full-body CT scan
• 80 000 µSv – The annual local dose to localized spots at the bifurcations of segmental bronchi in the lungs caused by smoking cigarettes (1.5 packs/day).
• 175 000 µSv – Annual dose from natural radiation on a monazite beach near Guarapari, Brazil.
• 5 000 000 µSv – Dose that kills a human with a 50% risk within 30 days (LD50/30), if the dose is received over a very short duration.

As can be seen, low-level doses are common for everyday life.

See also:

Medical Exposures

In general, radiation exposures from medical diagnostic examinations are low (especially in diagnostic uses). Doses may be also high (only for therapeutic uses), but in each case, they must be always justified by the benefits of accurate diagnosis of possible disease conditions or by benefits of accurate treatment. These doses include contributions from medical and dental diagnostic radiology (diagnostic X-rays), clinical nuclear medicine and radiation therapy.

The medical use of ionizing radiation remains a rapidly changing field. In any case, usefulness of ionizing radiation must be balanced with its hazards. Nowadays a compromise was found and most of uses of radiation are optimized. Today it is almost unbelievable that x-rays was, at one time, used to find the right pair of shoes (i.e. shoe-fitting fluoroscopy). Measurements made in recent years indicate that the doses to the feet were in the range 0.07 – 0.14 Gy for a 20 second exposure. This practice was halted when the risks of ionizing radiation were better understood.

In the following points we try to express enormous ranges of radiation exposure as well as a few doses from medical sources.

• 1 µSv – Eating one banana
• 1 µSv – Extremity (hand, foot, etc.) X-ray
• 5 µSv – Dental X-ray
• 10 µSv – Average daily dose received from natural background
• 40 µSv – A 5-hour airplane flight
• 100 µSv – Chest X-ray
• 600 µSv – mammogram
• 1 000 µSv – Dose limit for individual members of the public, total effective dose per annum
• 3 650 µSv – Average yearly dose received from natural background
• 5 800 µSv – Chest CT scan
• 10 000 µSv – Average yearly dose received from natural background in Ramsar, Iran
• 20 000 µSv – single full-body CT scan
• 80 000 µSv – The annual local dose to localized spots at the bifurcations of segmental bronchi in the lungs caused by smoking cigarettes (1.5 packs/day).
• 175 000 µSv – Annual dose from natural radiation on a monazite beach near Guarapari, Brazil.
• 5 000 000 µSv – Dose that kills a human with a 50% risk within 30 days (LD50/30), if the dose is received over a very short duration.

As can be seen, low-level doses are common for everyday life.

Health Effects of Medical Exposures

The medical use of ionizing radiation remains a rapidly changing field. In each case, usefulness of ionizing radiation must be balanced with its hazards. Nowadays a compromise was found and most of uses of radiation are optimized. We must emphasize, eating bananas, working as airline flight crew or living in locations with, also increase your annual dose. Some medical treatments and diagnostic examinations also cause radiation doses. But it does not mean, that it must be dangerous. In each case, intensity of radiation also matters. It is very similar as for heat from a fire (less energetic radiation). If you are too close, the intensity of heat radiation is high and you can get burned. If you are at the right distance, you can withstand there without any problems and moreover it is comfortable. If you are too far from heat source, the insufficiency of heat can also hurt you. This analogy, in a certain sense, can be applied to radiation also from radiation sources.

In some cases of medical exposures, we are talking (except radiotherapy) about so called “low doses”. Low dose here means additional small doses comparable to the normal background radiation (10 µSv = average daily dose received from natural background). The doses are very very low and therefore the probability of cancer induction could be almost negligible. Secondly, and this is crucial, the truth about low-dose radiation health effects still needs to be found. It is not exactly known, whether these low doses of radiation are detrimental or beneficial (and where is the threshold). Government and regulatory bodies assume a LNT model instead of a threshold or hormesis not because it is the more scientifically convincing, but because it is the more conservative estimate. Problem of this model is that it neglects a number of defence biological processes that may be crucial at low doses. 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 many of these have shown adaptive response to low dose radiation resulting in reduced mutations and cancers. This phenomenon is known as radiation hormesis.

 

See also:

Medical Exposures

Radiation is all around us. In, around, and above the world we live in. It is a natural energy force that surrounds us. It is a part of our natural world that has been here since the birth of our planet. All living creatures, from the beginning of time, have been, and are still being, exposed to ionizing radiation. Ionizing radiation is generated through nuclear reactions, nuclear decay, by very high temperature, or via acceleration of charged particles in electromagnetic fields.

Radiation Exposures from Electricity Generation

In this chapter, we would like to discuss a very interesting fact. It is generally known, 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, power generation from coal also creates additional exposures, and, what is more interesting, while exposure levels are very low, 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 are defined as the sum of all individual effective doses in a group of people over the time 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
• 0.03 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 per cent of the world’s energy was produced by the coal cycle in 2010, and 13 per cent by nuclear, the normalized collective dose will be about the same:

• 0.7 – 1.4 man Sv/GW.a (man sievert per gigawatt year) for coal cycle
• 0.43 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.

The above doses are related to public exposure. If we consider occupational exposure, regarding the mining of rare earth metals needed for construction, by far the largest collective dose to workers per unit of electricity generated assessed by the UNSCEAR came from solar power, followed by wind power. For solar power, occupational collective dose normalized to energy is a factor of forty and eighty larger than for the nuclear fuel cycle and coal cycle, respectively.

Note that, the collective effective dose is often used to estimate the total health effects, but according to the ICRP this should be avoided (see more: Collective Dose).

Radiation Exposures from Nuclear Fuel Cycle

The nuclear fuel cycle is a process chain consisting of a series of differing stages. In general, nuclear fuel cycle consists of steps in the front end (the preparation of the fuel), steps in the service period (fuel burnup), and steps in the back end (reprocessing or disposal of spent nuclear fuel). Radiation exposures from nuclear fuel cycle are, according to UNSCEAR, evaluated from entire life cycle of nuclear fuel and this includes:

• uranium mining, milling and mill tailings,
• fabrication of fuel assemblies
• power plant operation (except accidents),
• spent fuel storage or reprocessing,
• disposal of radioactive waste,
• decommissioning activities.

The collective dose, which results from nuclear fuel cycle is:

• 130 man Sv for nuclear fuel cycle,

Almost half of the contribution to public exposures from the nuclear fuel cycle comes from discharges of natural radionuclides during uranium mining and milling activities.

The normalized collective dose (per gigawatt and year) is:

• 0.43 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.

In the following points we try to express ranges of radiation exposure from electricity generation together with doses from, which 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

The above doses are related to public exposure. If we consider occupational exposure, regarding the uranium mining, power plant workers etc., the collective dose is higher especially uranium miners. The miners are surrounded by rocks and sloshing through ground water that is exuding radon.

Note that, the collective effective dose is often used to estimate the total health effects, but according to the ICRP this should be avoided.

Radiation Exposures from Coal Cycle

The public is also exposed to radiation from so called “enhanced sources of naturally occurring radioactive material”. This means also industries such as metal mining, coal mining and power production from coal creates additional exposures due to densification of naturally occurring radionuclides. Coal is the predominant source of energy used to produce electricity today. Coal cycle is a process chain consisting of a series of differing stages. For the coal cycle, the life cycle includes:

• coal mining,
• power plant operation,
• coal ash deposits.

According to the UNSCEAR, power generation from coal and entire coal cycle contribute more than half of the total radiation dose to the global population from electricity generation. This statement will seem paradoxical to many readers, since it’s not commonly known that non-nuclear energy sources release any radiation into the environment. But power generation from coal also creates additional exposures to public. Even nuclear fuel cycle releases less radiation into the environment than coal cycle and any other major energy source.

The problem is coal itself and especially coal ash (fly ash). Coal, a combustible black or brownish-black sedimentary rock, contains a substantial amount of the radioactive elements uranium and thorium. According to the UNSCEAR, the average specific activity of both uranium-238 and thorium-232 in coal is generally around 20 Bq/kg (range 5-300 Bq/kg). Coal mines in Freital, Germany, which have uranium concentrations of 15000 Bq/kg coal, are an exception. Burning coal gasifies its organic materials, concentrating its inorganic components into the remaining waste, called fly ash. Around 10% of coal is fly ash. Fly ash is hazardous and toxic to human beings and some other living things, and fly ash also contains the radioactive elements uranium and thorium, which are concentrated by a factor of 10. It must be emphasized, even fly ash does not possess any health hazards to the public. There are a few restrictions on the use of fly ash in landfill and road construction. Most restrictions are on the use in building construction, where it can result in increased exposures especially from radon. In any case, we don’t want to cause any irrational fear of radiation from coal. It does not mean, that it must be dangerous. In case of radiation from electricity generation, the doses are usually very, very low. Moreover, these results cannot be used to determine whether one form of energy generation is preferable to another.

The collective dose, which results from coal cycle is:

• 670-1400 man Sv for coal cycle, depending on the age of the power plant,

When considering the amount of electricity generated in the year 2010 by each technology, the coal cycle resulted in the largest collective dose to the global public and workers combined, followed by the nuclear fuel cycle. Of the remaining technologies, geothermal energy and combustion of natural gas were the next largest contributors.

The normalized collective dose (per gigawatt and year) is:

• 0.7 – 1.4 man Sv/GW.a (man sievert per gigawatt year) for coal cycle

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

In the following points we try to express ranges of radiation exposure from electricity generation together with doses from, which 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

The above doses are related to public exposure. If we consider occupational exposure, regarding the coal mining and fly ash deposits, the collective dose is higher especially for coal miners. Coal miners as a group receive the largest collective dose of radiation, through enhanced exposure to naturally occurring radionuclides.

Note that, the collective effective dose is often used to estimate the total health effects, but according to the ICRP this should be avoided (see more: Collective Dose).

Health Effects of Radiation Exposures from Electricity Generation

We must emphasize, eating bananas, working as airline flight crew or living near coal or nuclear power plant increases your annual dose rate. But it does not mean, that it must be dangerous. In each case, intensity of radiation also matters. It is very similar as for heat from a fire (less energetic radiation). If you are too close, the intensity of heat radiation is high and you can get burned. If you are at the right distance, you can withstand there without any problems and moreover it is comfortable. If you are too far from heat source, the insufficiency of heat can also hurt you. This analogy, in a certain sense, can be applied to radiation also from radiation sources.

In case of radiation from electricity generation, we are talking usually about so called “low doses”. Low dose here means additional small doses comparable to the normal background radiation (10 µSv = average daily dose received from natural background). The doses are very very low and therefore the probability of cancer induction could be almost negligible. Secondly, and this is crucial, the truth about low-dose radiation health effects still needs to be found. It is not exactly known, whether these low doses of radiation are detrimental or beneficial (and where is the threshold). Government and regulatory bodies assume a LNT model instead of a threshold or hormesis not because it is the more scientifically convincing, but because it is the more conservative estimate. Problem of this model is that it neglects a number of defence biological processes that may be crucial at low doses. 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 many of these have shown adaptive response to low dose radiation resulting in reduced mutations and cancers. This phenomenon is known as radiation hormesis.

See also:

Man-made Sources

In general, nuclear fallout is the residual radioactive material from a nuclear blast that “falls out” of the sky after an atmospheric explosion.  Fallout can also refer to nuclear reactor accidents, although a nuclear reactor does not explode like a nuclear weapon. The isotopic signature of fallout from nuclear blast is very different from the fallout from a serious power reactor accident.

In case of radiation doses from fallout, we consider the residual radioactive material from nuclear tests (not from reactor accidents) that were performed particularly in the two periods from 1954 to 1958 and from 1961 to 1962. According to the UNSCEAR, about 502 atmospheric tests, with a total fission and fusion yield of 440 Mt, were conducted.

Special Reference: Sources and effects of ionizing radiation, Annex B. UNSCEAR. New York, 2010. ISBN: 978-92-1-142274-0.

Fallout from a nuclear tests consist of fission fragments and neutron activation products. When a blast takes place on the ground or in the atmosphere near the ground, large amounts of activation products are formed also from surface materials. The fallout is particularly significant in the neighborhood of the test site, since the larger particles and most of debris lands on the ground (local fallout). But smaller particles  may remain aloft in the upper atmosphere for years. These particles can be therefore distributed nearly uniformly around the world, and contribute to so called global fallout. Equivalent doses from global fallout dropped from about 130 μSv/year in 1963 to about 10 μSv/year in recent years.

See also:

Man-made Sources

In addition to chemical, nonradioactive carcinogens, tobacco and tobacco smoke contain small amounts of lead-210 and polonium-210 both of which are radioactive carcinogens. It must be emphasized, cigarettes and tobacco contain also 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 equivalent dose. Due to decay of polonium-210, the annual local dose to localized spots at the bifurcations of segmental bronchi in the lungs caused by smoking cigarettes (1.5 packs/day) is about 80 mSv/year. Heavy smoking results in a dose of 160 mSv/year. This dose is not readily comparable to the radiation protection limits, since the latter deal with whole body doses, while the dose from smoking is delivered to a very small portion of the body. Many researchers believe that doses from polonium-210 are the origin of the high incidence of lung cancer among smokers.

Recall, lead-210 and polonium-210 are daughter nuclei of radon-222. Radon-222 is a gas produced by the decay of radium-226. Both are a part of the natural uranium series. Since uranium is found in soil throughout the world in varying concentrations, also dose from gaseous radon is varying throughout the world. Radon-222 is the most important and most stable isotope of radon. It has a half-life of only 3.8 days, making radon one of the rarest elements since it decays away so quickly. An important source of natural radiation is radon gas, which seeps continuously from bedrock but can, because of its high density, accumulates at the ground. The fact radon is gas plays a crucial role in spreading of all its daughter nuclei. As radon-222 decays into lead-210, lead-210 can be attached to dust of moisture particles and it can be sticked to tobacco leaves. When these particles are concentrated by smoking and inhaled as smoke, some of lead-210 is retained by the body. Since lead-210 is a weak beta emitter, it does not cause major doses, but polonium-210 does.

See also: Radon – Health Effects

The polonium-210, the decay product of lead-210, emits a 5.3 MeV alpha particle, which provides most of equivalent dose. Alpha particles, that belongs to high-LET radiation, are fairly massive and carry a double positive charge, so they tend to travel only a short distance and do not penetrate very far into tissue if at all. However alpha particles will deposit their energy over a smaller volume (possibly only a few cells if they enter a body) and cause more damage to those few cells (more than 80 % of the absorbed energy from radon is due to the alpha particles). Therefore, the radiation weighting factor for alpha radiation is equal to 20. An absorbed dose of 1 mGy by alpha particles will lead to an equivalent dose of 20 mSv.

Special Reference: Sources and effects of ionizing radiation, Annex B. UNSCEAR. New York, 2010. ISBN: 978-92-1-142274-0.

See also:

Man-made Sources

Radiation is used in variety of medical examinations and treatments. Doses from medical radiation sources are determined, whether a person underwent a treatment or not. In general, radiation exposures from medical diagnostic examinations are low (especially in diagnostic uses). Doses may be also high (only for therapeutic uses), but in each case, they must be always justified by the benefits of accurate diagnosis of possible disease conditions or by benefits of accurate treatment. These doses include contributions from medical and dental diagnostic radiology (diagnostic X-rays), clinical nuclear medicine and radiation therapy.

The medical use of ionizing radiation remains a rapidly changing field. In any case, usefulness of ionizing radiation must be balanced with its hazards. Nowadays a compromise was found and most of uses of radiation are optimized. Today it is almost unbelievable that x-rays was, at one time, used to find the right pair of shoes (i.e. shoe-fitting fluoroscopy). Measurements made in recent years indicate that the doses to the feet were in the range 0.07 – 0.14 Gy for a 20 second exposure. This practice was halted when the risks of ionizing radiation were better understood.

In the following points we try to express enormous ranges of radiation exposure as well as a few doses from medical sources.

• 1 µSv – Eating one banana
• 1 µSv – Extremity (hand, foot, etc.) X-ray
• 5 µSv – Dental X-ray
• 10 µSv – Average daily dose received from natural background
• 40 µSv – A 5-hour airplane flight
• 100 µSv – Chest X-ray
• 600 µSv – mammogram
• 1 000 µSv – Dose limit for individual members of the public, total effective dose per annum
• 3 650 µSv – Average yearly dose received from natural background
• 5 800 µSv – Chest CT scan
• 10 000 µSv – Average yearly dose received from natural background in Ramsar, Iran
• 20 000 µSv – single full-body CT scan
• 80 000 µSv – The annual local dose to localized spots at the bifurcations of segmental bronchi in the lungs caused by smoking cigarettes (1.5 packs/day).
• 175 000 µSv – Annual dose from natural radiation on a monazite beach near Guarapari, Brazil.
• 5 000 000 µSv – Dose that kills a human with a 50% risk within 30 days (LD50/30), if the dose is received over a very short duration.

As can be seen, low-level doses are common for everyday life.

Health Effects of Medical Exposures

The medical use of ionizing radiation remains a rapidly changing field. In each case, usefulness of ionizing radiation must be balanced with its hazards. Nowadays a compromise was found and most of uses of radiation are optimized. We must emphasize, eating bananas, working as airline flight crew or living in locations with, also increase your annual dose. Some medical treatments and diagnostic examinations also cause radiation doses. But it does not mean, that it must be dangerous. In each case, intensity of radiation also matters. It is very similar as for heat from a fire (less energetic radiation). If you are too close, the intensity of heat radiation is high and you can get burned. If you are at the right distance, you can withstand there without any problems and moreover it is comfortable. If you are too far from heat source, the insufficiency of heat can also hurt you. This analogy, in a certain sense, can be applied to radiation also from radiation sources.

In some cases of medical exposures, we are talking (except radiotherapy) about so called “low doses”. Low dose here means additional small doses comparable to the normal background radiation (10 µSv = average daily dose received from natural background). The doses are very very low and therefore the probability of cancer induction could be almost negligible. Secondly, and this is crucial, the truth about low-dose radiation health effects still needs to be found. It is not exactly known, whether these low doses of radiation are detrimental or beneficial (and where is the threshold). Government and regulatory bodies assume a LNT model instead of a threshold or hormesis not because it is the more scientifically convincing, but because it is the more conservative estimate. Problem of this model is that it neglects a number of defence biological processes that may be crucial at low doses. 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 many of these have shown adaptive response to low dose radiation resulting in reduced mutations and cancers. This phenomenon is known as radiation hormesis.

Diagnostic X-rays – Radiation Doses

Diagnostic X-rays use a very small dose of ionizing radiation to produce pictures of the inside of the body. Diagnostic X-ray exams account for about 90% of the radiation dose the population receives from medical sources. Chest X-rays (about 100 µSv) are the most common and they account for about 25% of all X-ray exams, followed by X-rays of the shoulder, pelvis and limbs (another 25%) and dental X-rays (10%). Note that, there is no direct evidence of radiation ever causing any harm at the exposure levels encountered with diagnostic radiological examinations.

X-rays belong to so called low-LET radiation. It was discovered, biological effects of any radiation increases with the linear energy transfer (LET). 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, X-rays). This is because the living tissue can more easily repair damage from radiation that is spread over a large area than that which is concentrated in a small area. Of course, at very high levels of exposure X-rays can still cause a great deal of damage to tissues.

Nuclear Medicine – Radiation Doses

Nuclear medicine is a medical science that involves the application of radioactive substances for diagnostic and treatment purposes. Nuclear medicine uses a very small amounts of radioactive materials called radiotracers, which are taken internally, for example, intravenously or orally. Then, external detectors (gamma cameras) capture and form images from the radiation emitted by the radiotracers. Sometimes the radioactive drug can be used in the treatment itself: an example is the treatment of thyroid disease with I-131. Nuclear medicine imaging is unlike a diagnostic X-ray, where external radiation is passed through the body to form an image. It also provides unique information that often cannot be obtained using other imaging procedures.

Average effective dose for most nuclear medicine procedures varies between 0.3 and 20 mSv. The common bone scan with 600 MBq of technetium-99m has an effective dose of approximately 3.5 mSv. These doses can be compared with the average annual effective dose from background radiation of about 3 mSv.

Radiation Therapy – Radiation Doses

In radiation therapy, the aim of the treatment is to deliver a very high dose to the tumour, but as little dose as possible to the surrounding healthy tissue. In this case, we are not talking about low doses. Using beams of high-energy gamma rays from cobalt-60 or from accelerators, localized high dose of radiation is delivered to tumour and this radiation tend to kill tumour cells. The amount of radiation used in photon radiation therapy is measured in grays (Gy), and varies depending on the type and stage of cancer being treated.

For curative cases, the typical dose for a solid epithelial tumor ranges from 60 to 80 Gy (locally), while lymphomas are treated with 20 to 40 Gy. Note that, this is not the effective dose. A gray is unit of absorbed dose, which is defined as the amount of energy deposited by ionizing radiation in a tumour.

See also:

Man-made Sources

There are two distinct groups exposed to man-made radiation sources. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) itemized types of human exposures as:

• public exposure, which is the exposure of individual members of the public and of the population in general
• occupational radiation exposure, which is the exposure of workers in situations where their exposure is directly related to or required by their work

Occupational Exposure from Man-made Radiation Sources

As was written, occupational exposure is the exposure of workers in situations where their exposure is directly related to or required by their work. According to ICRP, occupational exposure refers to all exposure incurred by workers in the course of their work, with the exception of

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

In general, occupationally exposed individuals work in the following areas:

• Fuel cycle facilities
• Industrial radiography
• Radiology departments (medical)
• Nuclear medicine departments
• Radiation oncology departments
• Nuclear power plants
• Government and university research laboratories

Such individuals are exposed to varying types and amounts of radiation, depending on their specific jobs and the sources with which they work. For that reason, most regulatory bodies require to limit occupational exposure to adults working with radioactive material to 5000 mrem (50 mSv) per year. Toward that end, employers carefully monitor the exposure of these individuals using instruments called dosimeters worn on a position of the body representative of its exposure. In most situations of occupational exposure the effective dose, E, can be derived from operational quantities using the following formula:

The committed dose is a dose quantity that measures the stochastic health risk due to an intake of radioactive material into the human body.

See also: Dose Monitoring

See also:

Man-made Sources