DESCRIPTORS: (*Gamma rays, *Ionization chambers, Measurement following *Thermal neutrons, *Fission of *Plutonium, Radio active isotopes, Isotopic cross section.) (Radiochemistry, Analysis, Radioactive decay, Gamma emission.) (Test reactors, Nuclear reactions, Experimental data, Tables.) Gamma ionization chamber readings are given for the products of thermal neutron fission of Pu-239 for the period from 1 second to about 22 hours following fission. Using spectral data on U-235 fission products and ionization chamber efficieny with gamma energy, the energy release rate of Pu-239 fission products is determined as a function of time. The results are compared with those attained for U-235 fission products. (Author).

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