DELAYED GAMMA RAYS FROM FISSION. Technical Report, August 1, 1965--July 31, 1966.

Measurements of the energy spectrum of delayed gamma rays from the neutron fission of Pu^S^ ^jj^j ^2 35 ^g^e performed with a Nal detector at a number of time intervals between 2 ysec and 80 ysec.The data showed three new prominent gamma rays with energies of 205, 390, and 1330 keV; two unresolved gamma rays having energies of approximately 110 keV; and the six gamma rays with energies of 260, 460, 720, 850, 910, and 1250 keV which were observed in previous studies for t > 50 ysec after fission.Absolute intensities of the new gamma rays were obtained using the normalization factor derived from the relative intensities of the last six gamma rays and their previously determined absolute intensities.The 205-, 390-, and 1330-keV gamma rays probably result from the cascade decay of a single isomer which has a half life of 3.4+0.4ysec and fission yields of 1.30+0.32and 0.63+0.21percent per fission of Pu^^^ and U^^^, respectively.Half lives and yields were also obtained for the two 110-keV gamma rays, but the results are tentative because of uncertainties in the data.The fission yields, cascade gamma rays, and half lives' of the isomers responsible for early delayed gamma rays from U^^^ (n,F) and Pu^^^ (n,F) have been summarized and total intensities and energy emission rates of gamma rays with energies greater than 140 keV have been presented as a function of time after fission over the range from 2 ysec to 25 msec.