since exposures to people depend not only on half-life but also the © pathway of_ the radioactivity from the air or water into and out of the body and the effectiveness of the radiation given off. Further, there are many radionuclides formed in the fission process with a very short half-life (i. e., @ few seconds, minutes or hours). The half-life is so short that it is not meaningful to relate half-life to exposure. The problem with such categorization is illustrated by the following Table : Of relative radiotoxicity taken in part from International Atomic Energy Agency (IAFA) documents. ; * Fe This radiotoxicity classification is pased. upon the radiological and biological half-life as well as other factors related to inhalation. The classification of radiotoxicity changes wren / the radionuclides enter man by other routes such as ingestion. t Table* | Radiotoxicity High © Nuclide Plutonium-239 Strontium-90 Grams per | Half-life curle 24,360 years 27.7 years 16.2 6.96 x 10 -3 Type of radiation Alpha beta, plus . yttrium 90 gamma** Medium upper Medium lower Low Iodine-131 Strontium-89 8.08 days 50.5 days Phosphorous-32 14.22 days Tron-59, 45.1 days Uranium-235 7.1 x-:10Y Tritiun ¥daughter products 12.26 years years 8.06 x 1076 beta and gam 3.44 x 107? | beta, plus yttrium 89 3.49 x 107° beta 1.02 x 10-4 beta 2,03 x 10°? L.65 x 10° gamnea* beta alpha t Derived trom IAFA Tectmical Report Series No. 15, A Basic Toxicity Classi- fication of Radionuclides, 1963