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| Fig. 1: Three Types of Ionizing Radiation. (Source: Wikimedia Commons) |
Usually when people think of radioactive materials they think of uranium and plutonium. However, there are many different sources of radioactive materials that we come in contact with every day. Naturally Occurring Radioactive Material (NORM) is a radioactive element that originates in the earth's crust. [1] Some common NORMs are different isotopes of radium, radon, thorium, uranium, and potassium. [1-7] Radioactive isotopes can cause health problems to people in large exposure situations. For example, antiques such as some old clocks, watches, and instrument dials that glowed in the dark contained radium or tritium. [3] Dial painters would lick the paint brush to create a fine tip and the large exposure to the ionizing radiation from the radium in the paint caused bone cancer to develop in some of the painter's jaws. [3]
So what is ionizing radiation? Ionizing radiation is produced when electrons are stripped away from atoms. [2] Three types of ionizing radiation produced from radioactive decay are alpha particles, beta particles, and gamma rays. [2] Alpha particles are heavy particles that are composed of two protons and two neutrons. [2] The heaviest unstable radioactive isotopes from elements like uranium, radium, and polonium produce alpha particles that are very energetic. [2] However, since the alpha particles are so massive, they quickly lose energy which allows them to be easily stopped; for example with a sheet of paper as seen in Fig. 1. [2] While alpha particles do not have enough energy to penetrate the outer layer of human skin, alpha particles can cause damage to living tissue and DNA if they are inhaled or swallowed. [2] The second type of ionizing radiation comes from beta particles. [2] Beta particles are small particles that are produced during radioactive decay from unstable atoms such as H-3, C-14, and Sr-90. [2] While beta particles can penetrate human skin and cause skin burns, beta particles create the most damage to living tissue and DNA when ingested. [2] Beta particles can also travel further than alpha particles and can be stopped by a thin layer of clothing or metals like aluminum shown in Fig. 1. [2] The third type of ionizing radiation is gamma rays. [3] Gamma rays are mass-less waves of photons that can penetrate through the human body causing damage to tissue and DNA. [2] As seen in Fig. 1, in order to stop the penetrating gamma rays, very dense materials such as inches thick lead or feet of concrete need to be employed. [2]
Radiation is all around us from sources that are natural and man-made. Even though we cannot eliminate radiation from our surroundings, we should be aware of the sources of radioactive materials. This will focus on sources of NORM found on Earth and from space.
NORM that originated from the Earth's crust is referred to as primordial radionuclides. [4] Where radionuclides are radioactive atoms with unstable nuclei. Examples of primordial radionuclides found in the soil are U-235, U-238, Th-232, and K-40. [4] These radionuclides have very long half-lives of hundreds of million years and are captured in the rock-cycle. [4] Radionuclides can also become incorporated into the soil as a result of industrial processes, nuclear fallout from atmospheric testing of nuclear weapons, accidents from nuclear plants, or improper storage of nuclear waste. [4] The radionuclides that are concentrated and produced from industrial processing are typically categorized as technologically-enhanced naturally-occurring radioactive material (TENORM). [5] One example of generating TENORMs is from the waste produced by drilling for oil and gas. [5] Primarily Ra-226, Ra-228, and Rn were found in the fluids and mud created to drill for oil and gas. [5] These radionuclides are then released in the surrounding environment as the radon gas escapes into the atmosphere and the water and mud are placed into ponds or pits for evaporation, re-use, or recovery. [5] This can put the workers at an increased risk of developing cancer if they inhale the radon gas or are too exposed to the gamma rays and beta particles generated by the radium isotopes. [5] As a result of this risk, safety guidelines are put into place to protect the workforce and public from radiation exposure. [5] Another industrial source of TENORM originates from coal-fired power plant emissions. [6] Uranium and thorium, along with their radioactive decay products, and K-40 are not consumed when burning coal and are therefore concentrated in the resulting ash. [6] Fly ash is the portion of the ash produced after burning the coal that is too small to be captured and escapes from the boiler and goes into the atmosphere. [6] The problem with fly ash is that it contains some of the radionuclides thus becomes another source of TENORM. [6] Current regulations are helping to encourage the use of better technology to capture and reduce the amount of fly ash that escapes into the atmosphere consequently reducing the worker's and public's exposure to the radioactive particles. [6] The implementation of technology to reduce the amount of fly ash into the environment is very important in reducing the health risk to everyone surrounding the coal power plant, because a coal burning power plant producing fly ash releases 100 times more radiation than a nuclear power plant producing the same amount of energy. [7]
According to the EPA in 2006, 8% of our radiation exposure derives from outer space including from our sun. [8] Cosmogenic radionuclides are produced and deposited by stable nuclides of atoms being bombarded by cosmic ray interactions. [4] Examples of cosmogenic radionuclides include: C-14, H-3, and Be-7 and the majority of these radionuclides have shorter half-lives compared to primordial radionuclides. [4] Exposure to cosmic radiation increases with increasing elevation therefore people who live in higher elevations and/or fly on airplanes experience a higher dose of cosmogenic radionuclides. [8] While radon is absorbed through breathing and cosmic particles are absorbed through the skin, the air provides shielding between us and cosmic radiation. [8] Thus the more air between us and space, the more shielding we have from cosmic radiation. [8]
It is known that too much exposure to radioactive materials, including NORM and TENORM, has health consequences including causing cancer, damaging human tissue, and DNA. [2-8] Therefore, it is important to be aware of the sources generating radiation and how you can protect yourself and reduce exposure to NORM.
© Andrea Eller. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] P. T. Underhill. Naturally Occurring Radioactive Materials: Principles and Practices, (CRC Press, 1996) pp. xi and 2.
[2] "Radiation: Fact, Risks, and Realities," U.S. Environmental Protection Agency, EPA-402-K-10-008, April 2012.
[3] "Radioactive Materials in Antiques" U.S. Environmental Protection Agency, EPA 402-F-06-024, April 2006.
[4] "Radionuclides in Soil" U.S. Environmental Protection Agency, EPA 402-F-06-051, April 2006.
[5] "Radioactive Waste from Oil and Gas Drilling" U.S. Environmental Protection Agency, EPA 402-F-06-038, April 2006.
[6] "Coal-Fired Power Plant Emissions" U.S. Environmental Protection Agency, EPA 402-F-06-028, April 2006.
[7] M. Hvistendahl, "Coal Ash Is More Radioactive than Nuclear Waste" Scientific American, 13 Dec 07.
[8] "Radionuclides in Air" U.S. Environmental Protection Agency, EPA 402-F-06-048, April 2006.
