AbstractEPR microwave power saturation technique has been applied to the systems of radiation‐induced radicals in protiated and wholely deuterated 3‐methylpentane to obtain the information concerning the high local spin concentration and radiation energy deposition mechanism. Evidences of spin‐spin interactions have been given from the studies of isothermal decay of these trapped radicals at 77°K. The annealing of the matrix is shown to have almost no effect on the relaxation times of radicals. The influence of nuclear magnetic moment on the spin‐lattice relaxation process of radicals is revealed and discussed on the basis of experimental results from the deuteration of the compound