Nuclear information obtainable from low energy neutron spectroscopy

Abstract

The results of measurements of thermal-neutron cross sections, level distributions in the resonance region,${{\overline {\Gamma _n^0 } } \mathord{\left/ {\vphantom {{\overline {\Gamma _n^0 } } D}} \right. \kern-\nulldelimiterspace} D}$ ratios, and determinations of the effective nuclear radius from potential:.scattering of slow neutrons are considered.

A discrepancy in the results of measurements of the thermal-neutron fission cross secticn in U²³⁵ is noted. The distribution of levels exhibits a deficiency in small spacings as compared with a random distribution, i. e., there seems to be a “repulsion” of levels. The dependence of${{\overline {\Gamma _n^0 } } \mathord{\left/ {\vphantom {{\overline {\Gamma _n^0 } } D}} \right. \kern-\nulldelimiterspace} D}$ on atomic number A is nonmonotonic, in accordance with the complex-potential model of the nucleus; however there is a considerable discrepancy between the experimental data and theory for atomic numbers in the neighborhood of 100. The effective radius determined from potential scattering of slow neutrons indicates a nonmonotonic dependence on A, in agreement with the model of a semi-transparent nucleus with smeared-out edges.