Report on 238Pu(n,x) surrogate cross section measurement

The goal of this year's effort is to measure the {sup 238}Pu(n,f) and {sup 238}Pu(n,2n) cross section from 100 keV to 20 MeV. We designed a surrogate experiment that used the reaction {sup 239}Pu(a,a{prime}x) as a surrogate for {sup 238}Pu(n,x). The experiment was conducted using the STARS/LIBERACE experimental facility located at the 88 Inch Cyclotron at Lawrence Berkeley National Laboratory in January 2010. A description of the experiment and status of the data analysis is given. In order to obtain a reliable {sup 238}Pu(n,x) cross section we designed the experiment using the surrogate ratio technique. This technique allows one to measure a desired, unknown, cross section relative to a known cross section. In the present example, the {sup 238}Pu(n,x) cross section of interest is determined relative to the known {sup 235}U(n,x) cross section. To increase confidence in the results, and to reduce overall uncertainties, we are also determining the {sup 238}Pu(n,x) cross section relative to the known {sup 234}U(n,x) cross section. The compound nuclei of interest for this experiment were produced using inelastic alpha scattering. For example, {sup 236}U(a,a{prime}x) served as a surrogate for {sup 235}U(n,x); analogous reactions were considered for the other cross sections. Surrogate experiments determine the probabilitiesmore » for the decay of the compound nuclei into the various channels of interest (fission, gamma decay) by measuring particle-fission (p-f) or particle?gamma (p?g) reaction spectra. By comparing the decay probabilities associated with the unknown cross section to that of a known cross section it is possible to obtain the ratio of these cross sections and thus determine the unknown, desired cross section.« less