Average level width of the compound nucleus

Abstract

The ratio of average level width to average level spacing of the compound nucleus in a strongly-overlapping-resonance region has been obtained by the self-indication measurement of the fluctuations in the neutron total cross sections. The observed ratios for Al, Si, and S with the excitation energy of 11–13 MeV are explained in terms of the strong-interaction model of the compound-formation process, though the observed values for Mn, Fe, Co, Ni, Cu, and Zn are systematically smaller than the calculated ones. The fluctuation in the excitation function of the nuclear reaction is analysed under the condition that the energy resolution or the energy step of the measurement is much larger than the average total width and spacing of the compound states. An apparent period of the fluctuation and a width of the energy-correlation function of the cross section are obtained as functions of the resolution or the energy step. As a result of the present analyses, it is pointed out that the average level width of the compound nucleus is not necessarily larger than the one predicted by the above-mentioned simple model of the compound process.