Pu-239(N, 2n) Pu-238 Cross Section Measurement Using A Recoil Method

A new measurement of the Pu-239(n, 2n) Pu-238 cross section was performed at 7.1, 7.7, and 9.3-MeV incident neutron energy using an activation technique to help resolve inconsistencies in the existing database above the threshold of the reaction. The method is based on the collection of Pu-238 nuclei produced in the (n, 2n) reaction. Although never used before to obtain a neutron cross section, this recoil technics overcomes the difficulty of having deposits of Pu-239 of extremely high purity. The collection efficiency must be determined using previously published data at higher energy, and our measurements are relative to these points. The neutrons were produced via the H-2(d, n) He-3 reaction. The incident neutron flux was determined via the Al-27(n,alpha) Na-24 standard reaction. The present measurements are consistent with the previous data and disagree with the JEFF3.3 evaluation.