An electron spin resonance study of radiation damages of epoxy resins at liquid helium temperature

Radiation damages produced at liquid helium temperature in epoxy resins, which are expected to be used as insulators of superconducting magnets for fusion reactors, have been studied by ESR technique. The yields of radicals and their local concentrations have been measured for the four kinds of combinations of aromatic and aliphatic resins each cured with aromatic or aliphatic hardeners. The radical yield produced at 4 K was found to be lower with increasing aromatic constituents and the combination of an aromatic resin (bisphenol A diglycidyl ether) with an aromatic hardener (diaminodiphenyl methane) gave the lowest yield. The results suggest that the radiation protective effect of aromatic groups is preserved even at 4 K. The yields of radicals produced at 4 K in these epoxy resins are higher by 2-20% than those produced at 77 K, whereas the local concentration is as high as two times in the samples irradiated at 4 K. (author)