MEASURED COMPOSITE DELAYED NEUTRON SPECTRA FROM FISSION OF U-235, U-238 AND Pu-239 AND DERIVED SIX-GROUP SPECTRA
Department of Physics and Applied Physics
University of Lowell, Lowell, MA 01854, U.S.A.
Delayed neutron (DN) energy spectra have been measured as a function of delay time after fission for U-235, U-238 and Pu-239 using a helium jet transfer system for fission product transfer. Beta-neutron correlations were used for background suppression and for energy determination by the neutron time-of-flight method. Each spectrum spans a DN energy range of 0.01 - 4.00 MeV. The U-235 and Pu-239 spectra show marked similarity, while those from the fast fission of U-238 are considerably more energetic. DN six-group spectra for U-235, U-238 and Pu-239 have been deduced from these measurements using a constrained least-squares iterative method.
KEYWORDS: fission delayed neutrons; 235U, 238U, 239Pu; time-dependent spectra; derived six-group spectra