Strength Function Determinations Using Fast Neutrons

Abstract

Using the ${\mathrm{Li}}^7(p, n){\mathrm{Be}}^7$ reaction as a source of neutrons, strength function determinations have been made on a number of intermediate and heavy elements at average neutron energies between 65 kev and 360 kev. The strength functions $\frac{{〈{{\gamma }_l}^2〉}_{\mathrm{Av}}}{\overline{D}}$ are obtained from measurements of the deviation from exponential attenuation of the neutrons passing through a sample of the element being studied. Values of $\frac{{〈{{\gamma }_0}^2〉}_{\mathrm{Av}}}{\overline{D}}$ at lower energies exhibit qualitatively the dependence on atomic weight predicted by the optical model, in agreement with previous measurements. For elements in the region $A=90\mathrm{}$, the rapid increase with energy of the $\frac{{〈{{\gamma }_0}^2〉}_{\mathrm{Av}}}{\overline{D}}$ obtained assuming only $S$-wave interactions suggests appreciable $P$-wave interactions are taking place. The data for these elements have been analyzed to yield $\frac{{〈{{\gamma }_1}^2〉}_{\mathrm{Av}}}{\overline{D}}$.