NEUTRON INDUCED FISSION CROSS SECTION RATIOS FOR 232Th, 235,238U, 237Np AND 239Pu FROM 1 TO 400 MeVLos Alamos National Laboratory, MS D449, Los Alamos, New Mexico 87545 U.S.A. A.D. Carlson, O.A. Wasson National Bureau of Standards, Gaithersburg, Maryland U.S.A. N.W. Hill Oak Ridge National Laboratory, Oak Ridge, Tennessee U.S.A Time-of-flight measurements of neutron induced fission cross section ratios for 232Th, 235,238U, 237Np, and 239Pu, were performed using the WNR high intensity spallation neutron source located at Los Alamos National Laboratory. A multiple-plate gas ionization chamber located at a 20-m flight path was used to simultaneously measure the fission rate for all samples over the energy range from 1 to 400 MeV. Because the measurements were made with nearly identical neutron fluxes, we were able to cancel many systematic uncertainties present in previous measurements. This allows us to resolve discrepancies among different data sets. In addition, these are the first neutron-induced fission cross section values for most of the nuclei at energies above 30 MeV. |