Absolute measurement of the 242Pu neutron-capture cross section

The absolute neutron-capture cross section of Pu-242 was measured at the Los Alamos Neutron Science Center using the Detector for Advanced Neutron-Capture Experiments array along with a compact parallel-plate avalanche counter for fission-fragment detection. The first direct measurement of the Pu-242(n,gamma) cross section was made over the incident neutron energy range from thermal to approximate to 6 keV, and the absolute scale of the (n,gamma) cross section was set according to the known Pu-239(n, f) resonance at E-n,E-R = 7.83 eV. This was accomplished by adding a small quantity of Pu-239 to the Pu-242 sample. The relative scale of the cross section, with a range of four orders of magnitude, was determined for incident neutron energies from thermal to approximate to 40 keV. Our data, in general, are in agreement with previous measurements and those reported in ENDF/B-VII. 1; the Pu-242(n,gamma) cross section at the E-n,E-R = 2.68 eV resonance is within 2.4% of the evaluated value. However, discrepancies exist at higher energies; our data are approximate to 30% lower than the evaluated data at E-n approximate to 1 keV and are approximately 2 sigma away from the previous measurement at E-n approximate to 20 keV.