DELAYED GAMMA RAYS FROM FISSION.

Abstract : Studies of delayed gamma rays from fission at early times were conducted using the pulsed beams of neutrons and bremsstrahlung x rays from an electron linear accelerator to produce fissions. Measurements of the energy spectrum of isomeric gamma rays from the neutron fission of Pu239 and U235 were performed. The intensities of delayed gamma rays from the neutron fission of U235 and Pu239 were measured as a function of time between 60 microsec and 30 msec. Results of the spectrum and intensity measurements gave a complete description of delayed gamma rays from U235 (n, F) and Pu239 (n, F) for the time interval from 50 microsec to 30 msec. The intensities of delayed gamma rays from photofission of U235, Pu239, and U238 were measured at early times, starting at 2 microsec after fission. An intense short-lived component with an apparent half-life of a few usec was observed for all three cases of photofission. For both U235 and Pu239, the intensity of delayed gamma rays in the isomeric time region from photofission is almost the same as that from neutron fission but is appreciably lower in the plateau region. (Author)