Absolute measurements of the cross section for fission of235U by 1.9-MeV and 2.4-MeV neutrons using the method of time-correlated associated particles

Abstract

This paper presents the results of absolute TCAP measurements of 235U fission cross sections at neutron energies E n of 1.9 and 2.4 MeV. These energy points lie in the range 1-5 MeV, where the existing experimental data have the greatest discrepancy (10% or more) and are in two groups: with higher values of oj and a convex form of the dependence oj (En) and with lower values of oj and a concave form (i.e., the values of the cross sections cannot be brought into agreement by renormalization). The ENDF/BVlibrary estimate that is accepted at the present time is midway between the two. The results of previous TCAP measurements for 2.6-MeV neutrons belong to the group with lower values of aj. In this study, the D(d, n) 3He reaction at a deuteron-beam energy E d = 3 MeV was used to obtain neutrons. The reaction kinematics in this case is such that neutrons of the required energy are emitted into the rear hemisphere and the associated helions are emitted