The $\gamma$ γ -ray angular distribution in fast neutron inelastic scattering from iron

Abstract

The angular distribution of $ \gamma$ -rays emitted after inelastic scattering of fast neutrons from iron was determined at the n ELBE neutron time-of-flight facility. An iron sample of natural isotopic composition was irradiated by a continuous photo-neutron spectrum in the energy range from about 0.1 up to 10 MeV. The de-excitation $\gamma$ -rays of the four lowest excited states of 56Fe and the first excited state of 54Fe were detected using a setup of five high-purity germanium (HPGe) detectors and five LaBr3 scintillation detectors positioned around the sample at $ 30^\circ$ , $55^{\circ}$ , $90^{\circ}$ , $ 125^{\circ}$ and $150^{\circ}$ with respect to the incoming neutron beam. The resulting angular distributions were fitted by Legendre polynomials up to 4th order and the angular distribution coefficients $a_{2}$ and $ a_{4}$ were extracted. The angular distribution coefficients of three transitions in 56Fe are reported here for the first time. The results are applied to a previous measurement of the inelastic scattering cross section determined using a single HPGe detector positioned at $125^{\circ}$ . Using the updated $\gamma$ -ray angular distribution, the previous cross section results are in good agreement with reference data.