Download Reducing Your Risk of Radiation Exposure and

Reducing Your Risk of Radiation Exposure and Contamination
Kristina E. Huffman, M.M.Sc., D.A.B.R.; Licensed and Board Certified Medical Physicist;
Furloughed Alaska Airline First Officer
This fact sheet is designed to provide basic information pertaining to exposure from radioactive
materials as well as steps that can be taken to reduce the risk of exposure. Radiation in very general terms
refers to the transfer of energy from one body to another. It can take several forms: electromagnetic
waves such as x-ray and gamma radiation, or particulate in the form of alpha or beta particle emissions.
The difference between the two forms is important to providing the foundation for understanding how
you can reduce your risk from exposure.
X-ray and gamma radiation are very high energy electromagnetic waves. Unlike visible light and
radio waves, x-ray and gamma radiation possess sufficient energy to ionize (or separate an electron from)
an atom. This property of being able to ionize an atom is what poses the greatest hazard from exposure to
x-ray and gamma radiation. X-ray and gamma radiation are commonly used in the medical industry for
diagnostic imaging and therapeutic treatments. Radiation in these forms harnesses the energy of the
associated electromagnetic waves as they pass through the body. Exposure to x-ray and gamma radiation
does not result in any residual radioactivity in the body after the source of radiation is removed. Sources
of radioactive material that emit gamma-rays are considered inherently radioactive, but the gamma
radiation is a product of the process of radioactive decay. Since the radioactive sources are typically
sealed, the resulting exposure is still external or occurring from the outside of the body. Once the
radioactive source is removed, exposure no longer occurs. X-ray and gamma radiation have the ability to
penetrate deep within the human body. The higher the energy associated with the x-ray or gamma
radiation, the greater the penetrating ability. X-ray and gamma radiation are equivalent to one another,
but arise from different mechanisms. X-rays are the result of man-made processes or those not associated
with nuclear decay. Gamma radiation is always the result of nuclear decay processes.
Spectrum of electromagnetic radiation from high to low energy
Particulate radiation takes the form of particles which can hold a negative, positive or neutral
charge. Beta particles are electrons and are ejected from an atoms nucleus during radioactive decay.
Since beta particles have an associated charge, they will interact and slow down much faster in tissue than
electromagnetic radiation. Typically beta particles will only have a range of several feet in air or
approximately one centimeter in tissue. Separating yourself from a radioactive material decaying by beta
particle emissions will aid in reducing your exposure from external sources. Once a radioactive material
that is decaying via beta particle emission is ingested or inhaled, it can become a source of continual
1 irradiation internally to the body. Contaminated air, food, or water can introduce radioactive elements
internally and cause harm to tissues in the body. In the air, beta particles can easily be stopped by a thick
sheet of plastic or a glass of water which with serve to absorb the radiation.
Beta particle emission as the result of nuclear decay from a radioactive atom
Alpha particles consist of two neutrons (neutral particles) and two protons (positively charged
particle), and ire identical to a nucleus of a helium atom. Since alpha particles are heavy compared to
other types of radiation and have a residual positive electrostatic charge, they interact strongly with
material that they encounter and readily give up their energy in the process. If inhaled or ingested, alpha
particles continuously irradiate the body internally and can pose a hazard. In the air, alpha particles are
easily shielded by an object as thin as a sheet of paper.
Alpha particle: identical to the nucleus of a helium atom
As outlined above, different types of radiation differ in their mode of creation, their ability to
penetrate the body, and the hazards that they pose. Understanding the basic types of radiation will aid in
understanding the hazards posed by some of the common radioactive materials associated with nuclear
power plant incidents and accidents.
Penetrating ability and corresponding shielding for different forms of radiation
Unsealed radioactive sources or radioactive material that is dispersed readily in the air, present a
different hazard. Since unsealed sources can take the form of gases, liquids, and solids, they have the
ability to be retained by the body resulting in continuous internal exposure. Radioactive materials can
take the form of a volatile gas, powder, dust, liquid, or other solid. These sources can be transported from
one location to another by way of people, vehicles, or other modes of transport. Once present in food and
2 water supplies, it can be ingested and absorbed by the intestinal tract. Once airborne in the form of dust,
it can be inhaled into the lungs and either deposit locally in lung tissue or pass into the blood stream.
When a radioactive material enters the body, it subjects a person to a continual source of internal
exposure. Depending upon the type of radioactive material, it can be absorbed by the thyroid gland,
muscle tissue, or bone posing longer term health risks. Depending upon the type of radioactive material
the physical form, mode of uptake, and longer term risks will differ. Radioactive materials differ in the
type of radiation that they emit, the energy associated with the radiation, the mode of uptake within the
body, the time that it takes the body to eliminate the radioactive material, the tissues that tend to absorb
the radioactive isotope, the longer term risks associated with exposure to the isotope, and the types of
agents used to aid in protecting the body or facilitating elimination of the source. Understanding the
differences is an important aspect of reducing your risk from exposure to these radioactive elements.
Nuclear power plants harness energy from radioactive fuel rods. While the details of
understanding how a nuclear power plant operates are less important, understanding the types of
radioactive isotopes that pose a risk in an incident or accident is vital to reducing exposure risk. Fuel rods
are generally composed of heavy fissile material such as Uranium-235 and Plutonium-239 in the form of
metal oxides. These elements can be made to undergo a nuclear fission reaction, which serves as the fuel
source for the reactor. By-products of the fission reactions as well as natural radioactive decay of these
elements give rise to other radioactive elements. The most prominent and relevant elements include
Iodine-131, Cesium-137, and Strontium-90. In the event of a nuclear power plant accident, these
radioactive elements have the potential to cause harm if dispersed.
Iodine-131 (commonly abbreviated as I-131) is produced by the fission or splitting of Uranium
atoms. I-131 is a radioactive isotope and has the same physical properties as other forms of iodine, but
decays over time. Iodine is a non-metallic, purplish-black crystalline solid. It has the capability of
sublimating, which means that it can go directly from a solid to a gas without first becoming liquid.
Iodine sublimes to a deep violet vapor at room temperature. The radioactive iodine that is present in fuel
rods can be released uncontrollably into the atmosphere in a volatile gaseous form if the integrity of the
fuel rod is compromised. Radioactive iodine can enter the body through ingestion or inhalation. It
dissolved easily in water, thus posing a potential hazard to water supplies. It can settle on to grass or
other food supplies for cows, and be passed on to humans through their milk. Once it enters the body, it
is taken up by the thyroid gland through the blood supply. Since radioactive iodine has the same
chemical properties as non-radioactive iodine, the thyroid gland does not distinguish between the two
types. I-131 is also taken up in lesser quantities by other tissues in the body. As a general rule, I-131 has
an approximate 8 day nuclear half-life. This means that it takes 8 days for half of all of the I-131 atoms to
decay. As the I-131 decays, it emits a negatively charged particle called a beta particle. Once it enters
the body, radioactive iodine has a biological half-life of 100 days. This means that it takes the body 100
days to eliminate half of the radioactive iodine that it absorbs. During this time the I-131 continues to
irradiate the body internally, posing a longer term health risk. Long term exposure to I-131 can cause
nodules or cancer of the thyroid gland. A radio-assay of the thyroid gland can be used to estimate the
level of exposure to I-131. Since the thyroid gland readily collects iodine, potassium iodide tablets are
frequently administered to block the absorption of radioactive iodine by the thyroid gland in the event of
unintended exposure. If the thyroid gland collects an over-abundance of this non-radioactive iodine, any
further excess will remain in the blood and be eliminated by the body. It should be noted that
3 administering large doses of iodine in the form of potassium iodide tablets can have some serious health
effects and should only be taken in emergency situations at the recommendation of a health care
professional.
Cesium-137 (commonly abbreviated as Cs-137) is created when a Uranium or Plutonium atom
absorb a neutron particle and undergo fission. Cesium is a soft, malleable, silvery-white metal. It is one
of only three metals that take liquid form at near room temperature. It also binds to chlorides to form a
powder. Cs-137 has the potential to contaminate soil and even take the form of dust resulting in airborne
dispersion. Walking on contaminated soil can facilitate the spread of Cs-137 beyond the contamination
site. Once airborne, Cs-137 can disperse well beyond the initial area contaminated either in the air or
carried on the surface of objects, and result in contaminated water supplies. Cs-137 can enter the body
either through ingestion or inhalation. Once it enters the body, Cs-137 is distributed fairly uniformly in
the tissues of the body. As Cs-137 decays it emits a negatively charged particle (called a beta particle)
and a relatively strong gamma-ray. Due to the strong gamma-ray that is emitted during decay, Cs-137
poses a significant risk of both internal and external exposure. Despite its biological half-life being 70
days, Cs-137 has a nuclear half life of roughly 30 years. As a result, even after Cs-137 is eliminated from
the body, it continues to pose a hazard of exposure to those in the vicinity. Ingestion of Cs-137 can be
treated with the prescription agent Prussian Blue, which binds to it chemically and accelerates its
elimination from the body. Long term risks associated with Cs-137 exposure include increased cancer
risk.
Strontium-90 (commonly abbreviated as Sr-90) is a by-product of the fission of Uranium and
Plutonium used in nuclear reactors. Large amounts of Sr-90 were introduced into the atmosphere and
dispersed worldwide during weapons testing in the 1950s and 1960s. Similar to iodine, Strontium comes
in radioactive and nonradioactive forms. Both forms have the same physical properties. Strontium is a
soft malleable metal, similar to lead. It is very chemically reactive and only found naturally in
compounds. In its pure form Sr-90 has a silver luster appearance. When introduced to air it takes on a
yellowish appearance, and can additionally ignite when introduced to air under certain conditions. Sr-90
decays via beta particle emission, and has a nuclear half-life of roughly 29 years. This in turn means that
it takes 29 years for half of the Sr-90 to decay to its daughter products. Sr-90 has a biological half-life of
a little over 49 years, which in turn means that it takes the body 49 years to eliminate half of the Sr-90
that is absorbed by the body. In the decay process, Sr-90 decays to another isotope which also is
radioactive and undergoes further decay via beta particle emission. While Sr-90 can be inhaled as a
contaminant in dust, it is more commonly ingested through the intake of contaminated food and water
supplies. Once in the body, Sr-90 behaves in a similar chemical manner to calcium. As a result, it is
readily absorbed by bone and teeth. Roughly 70-80% of the Sr-90 that is ingested is eliminated by the
body. The other 20-30% is deposited in bone and approximately 1% is distributed throughout other
tissues in the body. Long term risks of internal Sr-90 exposure include bone cancer, cancer of the soft
tissues surrounding bone, and leukemia. The most common test for exposure to Sr-90 is bioassay through
urinalysis. The test, if performed soon after exposure, can estimate the relative exposure to Sr-90.
Seaweed and alginates found in large brown algae such as Kelp and Alaria have the potential to reduce
the amount of Sr-90 that is absorbed through the intestinal walls of the body. Studies at the EPA’s
Environmental Toxicology Lab in Oak Ridge Tennessee have also determined that alginates could bind to
and eliminate strontium-90 from the body including from bone tissue.
4 Basic radiation protection and good radiation safety practices involve employing three very
simple principles: (1) time, (2) shielding, and (3) distance. The principle of time translates simply into
minimizing the time that you are exposed to a radioactive source. If radioactivity is present in greater
quantities in the atmosphere, minimizing the time that you spend outside exposed to the general
atmosphere will help to reduce risk. The second principle of shielding involves placing something
between you and the source of radiation that will tend to absorb the radiation and provide a shielding
effect. As mentioned in previous paragraphs, different types of radiation require differing types of
shielding. While a thin barrier such as a mask, goggles, or protective clothing will protect against alpha
radiation, they will offer no protection from x-ray or gamma radiation which require lead or concrete to
adequately shield. Sealing clothing in a seal-proof bag will limit further contamination from any articles
that you are wearing that becomes contaminated with dust or other particulates. The third principle
involves providing the maximum amount of distance between you and the source of the radiation. The
greater the separation between you and the radioactive source will significantly reduce your risk of
exposure. Radiation exposure will be reduced by a factor of four every time that you double your
distance from the radioactive source. This is commonly referred to as inverse square law and offers an
excellent means for minimizing risk of exposure to radioactive sources.
Overall there are a number of steps that one can take to minimize and reduce the risk of exposure
in an environment with elevated levels of radioactivity. Remaining indoors will reduce exposure by
separating you from the source of the radiation. Buildings can serve as effective barriers from some air
borne radioactive isotopes. Once indoors, one can further reduce the risk of contamination by not using
sources of ventilation such as air conditioners that would tend to draw contaminated air from outside the
building. Drinking liquid and consuming food products that are known to come from sources that are not
contaminated is another means of reducing risk of internal exposure through ingestion. Drinking bottled
water is but one effective example of minimizing the risk of ingesting radioactive isotopes. In the event
that clothing or other articles are thought to have become contaminated, sealing them in an air-tight bag
(such as one with a zipper lock) will prevent further contamination. Washing contaminants off of the skin
will reduce the risk of continued exposure and even possible ingestion from contaminants that remain on
the skin surface. These are a few methods that can be taken to reduce exposure risk in an environment
where radioactivity is present. While many of the radioactive isotopes mentioned above are utilized in
the treatment of cancer, they do so by destroying cells. It is important to note that while this process aids
in the eradication of cancer as a short term effect, it can also lead to the formation of secondary cancers as
a longer term effect. This is an important concept to keep in mind when considering why it is important
to minimize exposure to these radioactive isotopes. Knowledge and performance of good radiation safety
practices can go a long way in minimizing the risk associated with radiation exposure.
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