Radiation Widths of Bound Nuclear Levels in the Vicinity of the Neutron Threshold

The radiation widths of bound nuclear levels excited by ($\gamma ,{\gamma }^{\prime }$) reactions in nuclei ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$, ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}$, ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{86}{}_{}{}^{}\mathrm{Sr}$, ${}_{}{}^{80}{}_{}{}^{}\mathrm{Se}$, and ${}_{}{}^{66}{}_{}{}^{}\mathrm{Zn}$ have been measured. The present results together with results published by other authors using ($\gamma ,{\gamma }^{\prime }$) reactions are summarized and compared with similar results obtained in capture reactions of thermal and resonance neutrons. The expected properties of the nuclear levels obtained by extrapolation of the giant-dipole resonance to lower energies are compared with the present experimental data. The fluctuation in partial radiative widths from these bound levels is shown to be compatible with the Porter-Thomas distribution.