Gamma-ray emission from 80–86As isotopes

Abstract

Activities of 80–86As were produced in (n, p) reactions on stable selenium nuclei, as fission products, and via β− decay from their germanium precursors. To separate arsenic and germanium from fission product mixtures, rapid chemical separations were applied. Gamma-ray emission from arsenic isotopes was studied in γ-single and γγ coincidence experiments. Partial decay schemes are proposed for 34 sec 81As, 14.0 sec and 19.1 sec 82As, 13.3 sec 83As, and 5.3 sec 84As. The delayed-neutron branch in the decay of 2.05 sec 85As was shown to preferentially populate several excited levels in 84Se while the ground state of 84Se is fed to 29 % only. The systematics of low-lying levels in doubly even selenium isotopes is extended up to mass number 86. Discontinuities in the systematics at N = 48 are interpreted as an indication of a soft character of the nucleus 82Se.