Neutrons and gamma-ray strengths

In the analysis of high-resolution capture γ-ray spectra one encounters many difficulties of which some are discussed. To arrive at unambiguous bound-state spins and parities, one generally needs the strengths of secondary γ-rays as determined from lifetimes, branching and mixing ratios. A new method of DSA lifetime measurements at high recoil velocities is described, in which the accuracy is increased by a factor of 10 as compared to conventional low-velocity DSA measurements. Statistics are presented on the strengths of some 1000 γ-ray transitions between bound states in light nuclei (A<45), from which recommended strength upper limits are derived for transitions classified according to character (E or M), multipolarity and isospin forbiddenness. (Auth.)