MEASURED COMPOSITE DELAYED NEUTRON SPECTRA FROM FISSION OF U-235, U-238 AND Pu-239 AND DERIVED SIX-GROUP SPECTRA


Walter A. Schier, David J. Pullen, Gus P. Couchell, Mahmoud, H. Haghighi, Eric S. Jacobs, Marcel F. Villani and Paul R. Bennett

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