Delta K forbiddenness in neutron capture resonances in 177Lu.

Abstract

Neutron capture resonances produced in $^{177}\mathrm{Lu}$ by thermal neutrons are shown to gamma decay with intensities which are dependent on a \ensuremath{\Delta}K selection rule. The difference between \ensuremath{\Delta}K- forbidden (and \ensuremath{\Delta}K-allowed) transition rates, corrected for the energy dependence, when summed over all forbidden (and allowed) transitions and divided by the number of transitions is 1.37 photons/${10}^{7}$ neutron captures/${\mathrm{MeV}}^{5}$ for the forbidden transitions and 5.49 photons/${10}^{7}$ neutron captures/${\mathrm{MeV}}^{5}$ for the allowed transitions which gives a ratio between forbidden and allowed transitions of 0.26. If we require that allowed and forbidden transitions only be compared within the same spin and parity group, many transitions are excluded because there are no forbidden transitions to negative parity states. The average values for the forbidden and allowed transition ensembles are then 0.59 and 1.31, respectively, giving a ratio of forbidden to allowed transition intensities of 0.45.