Neutron Giant Resonances—Nuclear Ramsauer Effect

Abstract

Three continuous families of broad maxima and minima are observed in neutron total cross sections between 0.1 and 100 Mev. All shift smoothly to higher energy with increasing mass number. The relationships among the families, their energy-mass number dependence, and their detailed locations can be understood in terms of a semiclassical treatment of a simplified optical model. The oscillations are seen to result from interference between the part of the neutron wave which has traversed the nucleus with the part which has gone around. This nuclear situation is analogous to the Ramsauer effect in electron interactions with noble gases. An alternative explanation of the broad maxima as due to resonances of single partial waves is not valid because in general several partial waves are simultaneously important and because the partial wave characteristics change rapidly as one traverses a continuous family of maxima. The widths of the broad maxima are related more to the parameters of the real potential well than to the depth of the imaginary potential well.