Inclusive neutron production by 337 MeV/nucleon neon ions on carbon, aluminum, copper, and uranium

Abstract

We measured inclusive double-differential cross sections at angles of 30, 45, 60, and 90 deg for the production of neutrons above about 12 MeV from 337 MeV/nucleon neon ions bombarding targets of C, Al, Cu, and U. Three different energy regions can be distinguished in the neutron spectra: (1) a low-energy "evaporation" region, (2) a high-energy exponential tail reflecting the internal momentum distribution of the nucleons, and (3) an intermediate energy region reflecting quasifree and preequilibrium processes. The intermediate-energy region becomes less pronounced with increasing angle and is almost nonexistent at 90 deg. This behavior is consistent with the interpretation that the intermediate-energy region consists mainly of scattering processes with a few direct collisions. The intermediate-energy region is relatively flat at the forward angles and merges into an exponential falloff at wide angles. The 30-deg spectrum from the carbon target shows a broad peak around 150 MeV, which we interpret as a signature of quasifree nucleon-nucleon collisions. Although the neutron detection threshold does not permit us to see the evaporation peaks, we do see evidence of the evaporation tails. The evaporation yields apparent in our spectra increase with the mass number of the target. The neutron spectra differ from proton spectra reported for similar targets at 385 and 393 MeV/nucleon. The neutron-to-proton cross section ratios are fit well by an intranuclear-cascade model calculation, but poorly by a "firestreak" model calculation.