The Distribution of Thermal Neutron Fluxes into the Self-Shielded Wall Equipped with a Medical Self-Shielded PET (Positron Emission Tomography) Cyclotron

The role of systematic evaluations of thermal neutron fluxes originated in various medical small radiation accelerator facilities has become more and more important to establish uniformly a clearance system about radioactivities of radioactive waste materials produced, for example, when those facilities would be decommissioned and improved. The purpose of this paper was to investigate the distribution of thermal neutron fluxes into the self-shielded wall at the PET cyclotron in Tokushima University Hospital.The distribution of thermal neutron fluxes was determined using the activation Au foil method of 197Au(n,γ)198Au reaction and the visualization was observed using the imaging plate (IP) of a long ribbon shaped activation Au thin foil. It was found that the thermal neutron fluxes were distributed from 6.65 × 10^6 cm^(-2) s^(-1) (at 1.5 cm distance from an inside wall into a polyethylene layer) to 1.20 × 10^2 cm^(-2) s^(-1) (at 71.0 cm distance into a heavy concrete layer), and also that the distribution trend of thermal neutron fluxes will be approximately consistent with that of the calculated data led by MCNP code. We have confirmed that it will be possible for the IP visualization of thermal neutron fluxes into the self-shielded wall at the PET cyclotron to reproduce those distribution quantitatively and over a wide area. KCI Citation Count: 0