Test of Statistical Theory of Nuclear Reactions at 24 keV

Neutron-activation cross sections have been measured for about 40 nuclei. An Sb-Be photoneutron source was used for the measurements. The cross sections were measured relative to ${\mathrm{I}}^{127}$, whose cross section was taken equal to 0.82 b. With these measured values of the cross sections, calculations were made using the statistical theory of nuclear reactions, to obtain information about the parameter $\xi =\frac{D}{2\pi \Gamma \gamma }$, where $D$ is the average level spacing and ${\Gamma }_{\gamma }$ the radiation width. These values of $\xi$ were compared with those obtained from low-energy resonance parameters. In general there is good agreement between the calculated and the observed values of $\xi$, which shows that the statistical theory is valid at this energy for all types of nuclei. It was also found that $\xi$ is a smoothly varying function of the capture cross section $\sigma$.