The nuclear level structure of 76As from a study of the 75As(n, γ) 76As reaction

Abstract

The neutron capture γ-radiation from the reaction 75As(n, γ) 76As has been studied using a Li-drifted, germanium detector. The energies of low-lying, excited levels are deduced from the high-energy γ-transitions. The level density is compared with a theoretical formula of Gilbert and Cameron. Coincidence spectra were measured with NaI(Tl) crystals, a five-crystal pair spectrometer being used for the measurement of high-energy γ-rays. A decay scheme has been proposed for the 302 and 515 keV levels, to which strong transitions are observed from the capturing state. The possible shell-model configurations of these levels, of the ground state of 76As and of the ground state of 75As are discussed. It is shown that the strong, high-energy transitions to the 302 and 515 keV excited levels may be due to a direct capture of thermal neutrons into shell-model p-states. The spins of the latter levels are predicted to be 1 + and 2 +.