Measurements of Secondary Neutrons Produced from Thick Targets Bombarded by High Energy Neon Ions

Following our preceding study on thick target neutron yields by He and C, we measured angular and energy distributions of neutrons produced by 100, 180 and 400 MeV/nucleon Ne ions stopping in thick carbon, aluminum, copper and lead targets using the heavy ion medical accelerator of the National Institute of Radiological Sciences. The neutron spectra in the forward direction have broad peaks which are located at about 60 to 70% of the incident particle energy per nucleon due to break-up process and spread up to almost twice as much as the projectile energy per nucleon. The neutron spectra at all angles consist of two components of cascade neutrons and evaporation neutrons. The phenomenological hybrid analysis of the moving source model for these two components and the Gaussian fitting of break-up process could well represent the measured thick target neutron spectra. The experimental results are also compared with the calculations using the HIC code, and the calculated results generally agree with the measured ones within a factor of 2 margin of accuracy for 180 and 400 MeV/nucleon Ne ions. This systematic study on neutron production from thick targets by high-energy heavy-ions is the first experimental work and will be useful for shielding design of high energy heavy ion accelerator facilities.