A systematic experimental study of thick-target neutron yield for high-energy heavy ions

Angular and energy distributions of neutrons produced by 100 and 180 MeV/nucleon He, 100, 180 and 400 MeV/nucleon C, 100, 180 and 400 MeV/nucleon Ne ions stopping in thick carbon, aluminium, copper and lead targets have been measured using the heavy ion medical accelerator of the National Institute of Radiological Sciences. The neutron spectra in the forward direction have broad peaks located at about 60-70% of the incident particle energy per nucleon due to break-up process and spreading up to almost twice as much as the projectile energy per nucleon. The neutron spectra at all angles consists of two components of cascade neutrons and evaporation neutrons. The experimental results are also compared with the calculations using the HIC and LCS codes, and the calculated results generally agree with the measured ones within a factor of 2 margin of accuracy, except around the high energy end in the forward direction. This systematic study on neutron production from thick targets by high-energy heavy ions is a first experimental work and will be useful in the shielding design of high-energy heavy ion accelerator facilities. (author)