Thick target neutron yields from 100- and 230-MeV/nucleon helium ions bombarding water, PMMA, and iron

Abstract The secondary neutrons produced from 100- and 230-MeV/nucleon 4 He ions, respectively, stopping in the thick nat Fe, PMMA and water targets are measured by the time of flight method combined with the pulse shape discrimination of liquid scintillation detectors. The experimental data show that the secondary neutrons were contributed from breakup of projectiles, emission from overlap regions of projectile nuclei and target nuclei, and evaporation of projectiles and target nuclei. The measured quantities, including the double-differential thick target neutron yields, angular distributions, and total neutron yields per ion, were benchmarked against model calculations with the PHITS, FLUKA, and MCNP Monte Carlo simulation codes. The default models implemented in these codes agree the experimental data well at intermediate-to-large angles in the low-to-intermediate energy range. However, the physics models implemented in the FLUKA and the PHITS codes under-predict secondary neutrons at energies higher than the specific beam energies by more than one order. The energy-integrated simulation yields at 0° differ from the measured values by −75% to 240%. The underestimation of low-energy neutron yields by the models at small angles for 230-MeV/nucleon 4 He projectiles on the light targets are as much as five times lower. Our results indicate that improvements are needed in the physics models used to describe 4 He-induced nuclear reactions for predictions of neutron production.