Measurement of Radioactivity Produced in Concrete at the J-PARC Accelerator Tunnel

This study addresses the production of radioactivity in concrete walls at the J-PARC facilities. It was found that the production of various radionuclides in concrete was largely dependent on elemental composition of the concrete and locations of concrete in the accelerator where dominant particles were different. The depth profiles of the radioactivity in the concrete walls were also investigated. A depth profile of nuclides induced by thermal neutrons demonstrated that fast neutrons were moderated and changed to thermal neutrons inside the concrete. These thermal neutrons also contributed to the production of radionuclides by thermal neutron capture reactions. Activation induced by high-energy muons were observed in concrete behind the hadron absorber in the Neutrino Beam-line. The different mechanisms of radionuclides production in concrete were also discussed.