α and 2 p 2 n emission in fast neutron-induced reactions on 60Ni

Background: The cross sections for populating the residual nucleus in the reaction _Z^AX(n_,x^{) Z -2 A -4}Y exhibit peaks as a function of incident neutron energy corresponding to the (n ,n^'α ) reaction and, at higher energy, to the (n ,2 p 3 n ) reaction. The relative magnitudes of these peaks vary with the Z of the target nucleus.

Purpose: Study fast neutron-induced reactions on ⁶⁰Ni. Locate experimentally the nuclear charge region along the line of stability where the cross sections for α emission and for 2 p 2 n emission in fast neutron-induced reactions are comparable as a further test of reaction models.

Methods: Data were taken by using the Germanium Array for Neutron-Induced Excitations. The broad-spectrum pulsed neutron beam of the Los Alamos Neutron Science Center's Weapons Neutron Research facility provided neutrons in the energy range from 1 to 250 MeV. The time-of-flight technique was used to determine the incident-neutron energies.

Results: Absolute partial cross sections for production of seven discrete Fe γ rays populated in ⁶⁰Ni (n ,α /2 p x n γ ) reactions with 2 ≤x ≤5 were measured for neutron energies 1 MeV<E_n<250 MeV . Hauser-Feshbach plus pre-equilibrium theoretical calculations are compared to the experimental results.

Conclusions: There is good agreement between experimental results and theoretical predictions at lower neutron energies while discrepancies appear at higher neutron energies. The cross section for producing an isotope in fast neutron-induced reactions on stable targets via α emission at the peak of the (n ,α ) and (n ,n^'α ) reactions is comparable to that for 2 p 2 n and 2 p 3 n emission at higher incident energies in the nuclear charge region around Fe.