Systematics of Neutron Separation Energies

Photoneutron thresholds for 73 isotopes have been measured by radioactivity and neutron detection methods using a 25-Mev betatron. The neutron separation energies inferred from the observed thresholds are in general agreement with the values predicted from mass data and reaction energies. Several discrepancies are observed between threshold and neutron binding energies where ground state transitions require a spin change $>~\frac{7}{2}$. For these nuclei, the threshold energies are consistent with neutron emission leaving the residual nucleus in an excited state.