Mechanical Properties of Organic Materials Used in Superconducting Magnets Irradiated by Gamma Rays at Liquid Nitrogen Temperature

Radiation resistance of organic materials used in superconducting magnets for a 50 GeV–750 kW proton beam line for the J‐PARC neutrino experiment was studied with respect to mechanical properties. Specimens cooled at a liquid nitrogen temperature of 77 K were irradiated by gamma rays from 60Co with the maximum dose beyond 10 MGy. The flexural strength of glass‐fiber reinforced plastics (GFRPs), the tear strength of polyimide films and the tensile lap‐shear strength of adhesive films were evaluated. It was verified that the organic materials used in the superconducting magnets have the sufficient radiation resistance, and the degradation of their mechanical properties after the 10 years operation was estimated to be negligible.