Neutron Energy Spectra at 180° from 140 MeV Proton Incident Reactions

The neutron energy spectra of carbon, iron, and gold targets with 140 MeV protons at 180 degrees were measured at the RCNP cyclotron facility using the time-of-flight technique. The results were compared with results calculated using the evaluated nuclear data file (the LA150 library) and the intranuclear cascade models (JAM and JQMD) implemented in the PHITS code. The results using LA150 and JQMD generally agreed with the experimental data except for the carbon target, but the JAM could not reproduce high-energy neutrons above 10 MeV because of the lack of pre-equilibrium reactions and the reflection and refraction of a nucleon with other nucleons in the nucleus, for example. Experimental neutron energy spectra at 180 degrees were composed of two evaporation Maxwellian-type components (in two neutron energy regions of 1 - 4 MeV and 4 - 10 MeV) and a preequilibrium (in the neutron energy region above 10 MeV) Maxwellian-type component All experimental spectra were fitted well by the sum of three Maxwellian-type equations across the entire energy region of the neutrons.