Nuclear level density of 59 Ni from analysis of differential neutron emission cross sections in 56 Fe (α, n) 59 Ni reaction

The results of measuring the spectra and angular distributions of neutrons in the 56 Fe (α, n) 59 Ni reaction at α particle energy of 16.3 MeV are discussed. The measurements are performed at the HI-13 tandem Van de Graaff accelerator by means of the multi-detector fast neutron time-of-flight spectrometer at angles from 20 deg up to 160 deg. The analysis of the data obtained is performed basing on the Hauser-Fescbach calculations with generalized superfluid model of nucleus and back-shifted Fermi gas model for the nuclear level density. The nuclear level density of 59 Ni and its model parameters are determined. The results of comparison with available systematics of nuclear level density are considered . It is shown that the comparison of the neutron spectra calculated and measured demonstrates a good fit of both discrete-level and continuum parts. Basing on comparison of the angular distributions measured and calculated in excitation energy range of 5.5 - 6.5 MeV an effective moment of inertia for 59 Ni is determined and spin cut-off parameter is calculated. The conclusion is made that the obtained results show essential deference from the predictions of level density systematics and neutron-resonance value