27Al(n,xγ) reactions for neutron energies from 3 to 400 MeV

The prompt gamma radiation from the interaction of fast neutrons with aluminum was measured using the white neutron beam of the WNR facility at the Los Alamos National Laboratory. Aluminum samples were positioned at about 20 m or 41 m distance from the neutron production target. The spectra of the emitted gamma rays were measured with a high-resolution HPGe detector. The incident neutron energy was determined by the time-of-flight method and the neutron fluence was measured with a U-238 fission chamber. From the gamma-ray spectra excitation functions for prominent gamma-ray transitions in various residual nuclei tin the element range from F to Al) were derived for neutron energies from 3 to 400 MeV. Up to 200 MeV incident neutron energy the results are compared with the predictions of nuclear model calculations performed with the code GNASH. This code combines compound nucleus calculations using Hauser-Feshbach statistical theory with preequilibrium calculations from an exciton model including multiple preequilibrium processes. For the majority of the gamma-ray transitions there is reasonable agreement between the measured and the calculated cross sections. [S0556-2813(98)04404-5].