Experiment Design of Secondary Neutron and Charged-Particle Measurement with Stopping Targets Bombarded by 100 and 230 MeV/amu ⁴He Ions

Stopping target measurements with energetic ion beams are important for building and validating physics models used to predict nuclear fragmentation fields created by interactions between incoming primary ions and target materials. However, the values of the ratio of primary ion range R to target depth d (R/d) are not the same in several of the existing measurements, and as such, this makes the intercomparison between those measurements complicated without corrections for differences in secondary particle transport through differing amounts of target material. Therefore, this work aims to study the influence of the target geometry on the angular distributions of secondary particles. Cases with 100 and 230 MeV/amu ⁴He ions bombarding stopping water and iron targets with various dimensions were studied by using the transport model code PHITS (Particle and Heavy Ion Transport code System). With increasing target depth, the impact on the attenuation of secondary particles is more significant for lighter target mass and higher-energy projectiles at forward angles. Also, with deeper targets, more interactions occur between the secondary particles and the target nuclei, which results in more targetlike fragments at large and backward angles. With respect to the cross-sectional area of the stopping targets, the forward angular distributions are similar to the system with smaller cross-sectional area of the targets; however, charged particles are significantly attenuated at large angles, whereas no general rule was found for secondary neutrons at large and backward angles. These results indicate that in order to compare the angular distributions from various stopping target measurements, it will be necessary to utilize a radiation transport code to correct the differences caused by target geometry.