Measurement of neutron-production double-differential cross sections of natC, 27Al, natFe, and natPb by 20, 34, 48, 63, and 78 MeV protons in the most-forward direction

In this study, the neutron-production double-differential cross sections (DDXs) of na^tC, ²⁷Al, na^tFe, and na^tPb bombarded by 20, 34, 48, 63, and 78 MeV protons were measured in the most-forward direction by the time-of-flight (TOF) method using a liquid organic scintillator. Characteristic peak structures were observed in the measured neutron spectra, especially for light nuclei. The experimental data were compared with the results from the Monte Carlo simulation code "Particle and Heavy Ion Transport code System" (PHITS) using the theoretical model Liège Intranuclear Cascade (INCL) or using the Japanese evaluated nuclear data library (JENDL-4.0/HE). While the results of JENDL-4.0/HE were in agreement with the experimental data better than those of INCL, neither could reproduce the measured peak structures for some combinations of the beam and target. For the energy-integrated cross sections, JENDL-4.0/HE reproduced the experimental data within a factor of two in all cases. On the other hand, INCL gave values up to approximately six times larger than the experimental ones.