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IONIZINC RADIATION Fig 42-3 The relotion*hip of various electromagnetic radiations in the energy spectrum Reprinted with permission from "Atomic Radiation," Q 1957 by RCA Semico Co, lne As a general rule, if a known radionuclide u present, the kind of radiation, the energy of die radiation, the decay chains or daugh ter products, and the tune necessary to reach a certain level of radiation can be predicted. Conversely, if an unknown radio nuclide is present, sufficient measurements will lead to precise identification of the radionuclide For example--because radionuclide of the element iron is chemically the same as its nonradioacfave counterpart, stable iron, some of it can be mixed with the nonradioacbve iron In order to tag it so that it can be followed in a process (or a corro sion test) to detenmoe what is happening to it By the same token, persons working with certain radioactive materials can easily de tect the presence of the radioactive materials in minute amounts In the case of a radio nuclide which has a very short half-life and which is disintegrating rapidly, the weight of the material may be very mmnt but die magnitude of the exposure to disintegrating atoms of the material may be very great Guide level concentrations may be found in Handbook 69 published by the National Bureau of Standards The statement that die acceptable breath ing levels of some materials are literally id terms of disintegrating atoms per day im plies that these materials are extremely toxic They are, but as a general rule they are still measurable and quickly detectable Many toxic (but not radioactive) materials are used routinely m industry, and it may take hours or days to evaluate the extent of the risk Radionuclides, in contrast, usu ally can be readily detected with appropri ate instruments Units of radiation measurement Radiation may be expressed in several different units The International Commis sion of Radiological Units and Measure ments (ICRU) issued a report0 m 1962 defining units and measurements Some of these units follow U S Department of Commerce, National Bureau of Standards, Washington, DC Radiation Quantities and Units Handbook 84. Nov 1982 See also National Safety Council Industrial Data Sheets Nos 461 and 475, 'Beta Ray Sealed Sources and X-Rays 'in Industry. 42-8