Ground-state photoneutron angular distribution for 14N

Abstract

Photoneutron angular distributions were measured for the reaction 14N(γ, n 0) 13N using neutron time-of-flight techniques over the region of excitation energy from 17 to 26 MeV. Coefficients of a Legendre polynomial fitted to the data are interpreted in terms of a simple single-particle nuclear model. For reactions to the ground state in 13N it appears that most of the photon absorption in the giant resonance region studied forms J π = 2 − states in 14N which decay by d-wave neutron emission. Some evidence was found for the existence of J π = 0 − strength at about 22.5 MeV (the peak of the cross section). The results are in general consistent with an identification of the (γ, n 0) process with the promotion of a p 1 2 neutron to the s-d shell. Little or no E2 or M1 absorption was observed. Comparison with photoproton measurements shows some evidence for a small amount of isospin T = 0 mixing also near 22.5 MeV. Comparison with calculations of the ground-state cross section shows reasonable agreement if the theoretical results are displaced upwards in energy by about 1 MeV.