Some activation measurements and a comparison with theoretical (n, 2n) cross sections and isomeric cross section ratioss

Abstract

Cross sections are measured for the reactions Co 59(n, 2n), Zn 64(n, 2n) and Zn 64(n, p) in the energy range 13.8–14.8 MeV. At 14.7±0.3 MeV a value of 20±5 μb is obtained for the S 32(n, t) cross section and an upper limit of 0.1 mb for Ca 40(n, t). The Co 58 isometric cross section ratio for the (n, 2n) reaction and ratios reported for other reactions leading to Co 58 are compared with theory and shown to be consistent with a value of approximately 4 for the parameter σ which characterises the dependence of the nuclear level density on angular momentum. Using nuclear temperatures derived from spectrum measurements(n, 2n) cross sections calculated from the Weisskopf-Ewing formula are shown to be in good agreement with experimental results for cases in which the implicit theoretical assumption (that the second particle emitted is always a neutron) is valid. A simple criterion is derived to identify cases in which the assumption is invalid.