S. S. Kovalenko

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

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

Cross section of the237Np(n, 2n)236Np(22.5 h) reaction, caused by252Cf spontaneous fission neutrons

The authors used the direct method of determining sigma /sub n,2n/ on /sup 252/Cf spontaneous fission neutrons. The cross section of the reaction was measured by means of the relative method using activation threshold detectors with known cross sections for neutrons from the Cf spectrum. A figure shows response functions of various threshold reactions with respect to the spectrum of /sup 252/Cf spontaneous fission neutrons. It was necessary for the authors to determine which of the cross sections contained the larger systematic error.

The long-lived236Np isomer's fission cross section for thermal neutrons

Conflicting findings on the correlations between fission cross section and target-nucleus spin for several nuclei, viz., a large cross section corresponding to a high spin, prompted the authors to verify such a correlation by repeating the measurement of the familiar fission cross section of Np 236 (zeta) by using analogous methods of chemical purification of the substance and identification of the fragments as were used in the case of Np(s) 236.

Measurement of the cross sections of the reaction237Np(n, 2n)236Np (22.5 h) for neutron energies in the range 7–10 MeV

This paper presents experimental results of the study of the energy dependence of the cross section for the formation of /sup 236/PU in the reaction /sup 237/Np (n, 2n). Together with the results for neutron energies near 14 MeV, they present the possibility for describing this cross section in the entire energy interval of importance for fast reactors. The urgency of a theoretical study of the reaction examined here remains, taking into account the quantum characterisitics of the low-lying levels.