Radiation protection study for the J-PARC neutrino experimental facility

The characteristics of radiation and radioactivity in the Japan Proton Accelerator Research Complex (J-PARC) neutrino experimental facility have been investigated under the 30-GeV proton beam operation below 145 kW in order to estimate the maintenance scenario and the environmental impact for the future high power operation up to 750 kW. The radioactivity produced in the magnetic horn cooling water and helium gas in the helium vessel which were installed around the target and the concrete and soil behind the beam dump has been measured in relation to the beam power. These activity concentrations under the high power operation (750 kW for 20 days) are estimated from the measured results to be up to two hundred times of the regulation value for the disposal in Japan. The depth profiles of the radioactivity produced in the concretes behind the beam dump show constant distributions on the beam axis, while those at off-beam axis show exponential attenuation with increasing the concrete depth. (author)