Radiological Risk Assessment for King County Wastewater Treatment Division Page: 18 of 51
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2.3 Characteristics of Radioactive Materials that May Be Used for Malicious
Purposes
The characteristics of selected radionuclides are given in the Table 1. These are of particular interest
because they are plentiful in relatively large amounts. Half-lives and principal radiation types are shown.
The D-values are internationally-recognized dangerous amounts of these radionuclides (International
Atomic Energy Agency (IAEA) 2003) in units of curies or terabecquerels (TBq), where 1 Ci = 0.037
TBq. For the most common chemical forms of these radionuclides, note the incredibly small mass
associated with a dangerous amount of radioactivity. As shown in the last three columns, these
radioactive materials may have industrial, medical, or defense uses.
Table 1. List of radionuclides of concern. Some emit more than one kind of radiation. D-values are
threshold values for dangerous amounts in curies, terabecquerels, and milligrams (mg) if the
radionuclide is not diluted with non-radioactive material. Use or origin indicates where the
radionuclides may be in use.
Radiation D-value Use or
Origin
Radionuclide Symbol Half-life c Ci TBq mg
co E
co .0 D)_ _
cobalt-60 60Co 5 years p y 0.8 0.03 0.7 x x
strontium-90 Sr 28 years p 30 1 450 x x
molybdenum- 99Mo 66 hours p y 8 0.3 0.017 x
99
iodine-131 I 8 days p y 5 0.2 0.04 x
cesium-137 Cs 30 years p y 3 0.1 44 x x
iridium-192 Ir 75 days p y 2 0.08 0.2 x x
radium-226 226Ra 1600 years a p y 1 0.04 1,000 x
uranium U4.5 billion a weak - x x
years
americium-241 Am 432 years a y 2 0.06 580 x x
plutonium Pu 24,000 years a p weak 2 0.06 - x x
2.4 Amounts that affect humans
Radiation is like money in one sense: you can't talk meaningfully about it unless you know how much
you're talking about! There are amounts of radioactive material that are so small that they are of no
concern.
Furthermore, radioactive materials exist in nature. Radioactive uranium, thorium and potassium-40 are
primordial radioactive materials that have been on earth since the dawn of time. They are found
everywhere and occur in trace amounts in all food and beverage. All human beings have eaten these trace
amounts all of their lives, and all contain traces of these radioactive materials.8
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Strom, Daniel J. Radiological Risk Assessment for King County Wastewater Treatment Division, report, August 5, 2005; Richland, Washington. (https://digital.library.unt.edu/ark:/67531/metadc902140/m1/18/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.