Investigation of the 56Fe(n, γ) 57Fe and 58Fe(n, γ) 59Fe reactions

Abstract

The γ-radiation has been investigated produced by thermal neutron capture in a natural Fe sample and in a sample enriched in 58Fe. Of the 253 γ-rays ascribed to the 56Fe(n, γ) 57Fe reaction, 191 have been placed in the 57Fe level scheme (of which 124 placements are new); of the 138 γ-rays observed in the 58Fe(n, γ) 59Fe reaction 68 have been placed (with 55 new placements). Excitation energies (with 0.02–0.7 keV error) and branching ratios have been determined of 60 bound levels in 57Fe and of 27 in 59Fe. The Q-values of the 56, 58Fe(n, γ) reactions amount to 7646.0 ± 0.2 and 6581.0 ± 0.2 keV, respectively. One can conclude that J = 3 2 for the 2836 keV level in 57Fe, and that J π = 3 2 − for the 2570, 3072, 3104, 3160 and 3384 keV levels in 59Fe. A shell-model calculation has been performed with up to two holes in the 1 f 7 2 sub-shell and particles in the 2 p 3 2 , 1 f 5 2 and 2 p 1 2 sub-shells. The energies of low-lying 57, 58,59 reproduced with a mean deviation of 0.17 MeV. The surface-delta interaction appears superior over the Kuo-Brown interaction in explaining the electromagnetic properties of the lowest six states of 57Fe.