Investigation of Dose Rate Distribution in an Experimental Hall of a RIKEN Accelerator-Driven Compact Neutron Source Based on the ⁹Be(p, n) Reaction With 7 MeV Proton Injection

To characterize the dose rate distribution in an experimental hall of a RIKEN accelerator-driven compact neutron source (RANS) based on the
⁹
Be(p, n) reaction with 7 MeV proton injection, systematical measurements and calculations for neutron and gamma-ray dose rates by GEometry ANd Tracking (GEANT), Particle and Heavy Ion Transport code System (PHITS), and Monte Carlo N-Particle (MCNP) codes were performed. Calculations always underestimated measurements when proton beam loss effect was not considered. Relatively good agreements were observed among the different simulation codes. To explain the underestimations, the additional dominant neutron and gamma-ray sources due to proton beam loss were identified at the position around exit of the drift tube linac (DTL), made of copper, and the beam pipe from quadrupole (Q) magnets to steering (ST) magnets, made of aluminum, from measurements with placing collimators along linac. The beam loss fractions of 2%–3% on copper and 1% on aluminum, respectively, were the most appropriate estimation. In addition, we proposed the possible measures to reduce the measured total dose rate of
$3.8~\mu $
Sv/h at the operator position in the control room, with the addition of a wall at the entrance of experimental hall and extension of borated polyethylene (BPE) at the end of the beam. As a result, the dose rate became 2.5 times lower than the current one.