Method of spin assignment of bound levels populated by (n, γ) reactions

The conditions are examined under which the spin of low-lying levels may be deduced from a comparison of the probabilities of populating such levels with γ-cascades starting from neutron capture states with different spins. To test this spin-assignment method low-energy γ-ray spectra from neutron capture in single resonances of¹⁰⁵Pd and ¹⁷⁷Hf have been measured, and the relative intensities of γ-transitions from low-excitation levels have been determined. For each level the ratio between its populations from two different initial spin states is obtained and is found to provide a firm indication of the level spin. The experimental values of the population ratios are compared with the values obtained by a general formula based on simple statistical assumptions and by more realistic Monte Carlo calculations of the γ-cascade. The perspectives of the method are discussed.