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D. G. OLSON, 194 Meat Lab, Iowa State University, Ames, IA 50011

There are two types of irradiation sources that can be used for food. These sources are radioactive nuclides and electricity. The two radioactive nuclides that are approved are cobalt-60 and cesium-137. Both of these nuclides emit gamma rays, which are photons containing no mass. The gamma rays have energies from .66 to 1.3 MeV allowing deep penetration into foods. Absorption of energy of the gamma rays decreases exponentially as it travels through the food. At least two sides of the boxes or pallets containing food need to be exposed to the source to obtain the lowest maximum-to-minimum dose ratio. Licensing of gamma facilities is controlled by the Nuclear Regulatory Commission or by Agreement States. Using electricity, electrons are generated and accelerated to energies up to 10 MeV, which is the highest electron energy permitted for foods. Electrons have a small mass which limits penetration into foods. With 10 MeV electrons, depth of penetration into foods, with densities similar to water, is limited to about 3.7 cm with one-sided exposure or about 8.6 cm with two-sided exposure. Depth of penetration decreases at lower electron energies. Electron energy can be converted to x-rays by placing a metal (usually tungsten or tantalum) target in the electron beam path. Conversion to x-rays is limited to electrons with energies no greater than 5 MeV. X-rays are photons with no mass and can penetrate foods similar to gamma rays. There is only about 8% efficiency in the conversion of electron energy to x-ray energy. Very high powered electron beam machines would be needed in x-ray production facilities to account for the low conversion efficiency. Licensing of electron beam facilities is controlled by State Departments of Public Safety.