Nuclear Science and Engineering / Volume 141 / Number 2 / June 2002 / Pages 140-153
Neutron energy spectra penetrated through concrete shields were measured using three types of high-energy neutron detectors: the Self-TOF detector, an NE213 organic liquid scintillator, and Bi and C activation detectors, which have been newly developed by a group at the Heavy-Ion Medical Accelerator in Chiba (HIMAC) facility of the National Institute of Radiological Sciences, Japan. Neutrons were generated by bombarding 400 MeV/nucleon C ions on a thick (stopping-length) copper target. The neutron spectra were obtained through an unfolding code with their response functions and compared with LAHET and MCNPX calculations combined with the LA150 cross-section library. The calculations tend to overestimate with increasing the shielding thickness compared to the experimental results. The neutron fluence measured by the NE213 detector was simulated by the track length estimator in the MCNPX code, and the contribution of the room-scattered neutrons was evaluated. The neutron fluence attenuation length was obtained from the experiment for each detector and the calculation in the energy range of 20 to 800 MeV.