Some studies of the effect of irradiation on the neutron small angle scattering from graphite

The small angle scattering from a number of graphites which had been neutron irradiated at 10500C to doses up to 5 x 1021 n.cm-2 (Dido Nickel Equivalent) has been studied. Irradiation results in a decrease in the number of pores and regions of disorder whose radius of gyration is approximately 100 A and an increase in the number whose corresponding dimensions are approximately 25 A. Fractional changes in the volume of these samples, due to irradiation, were also studied and the well known shrinkage, followed by turn-around and expansion with increasing dose observed. However, it was not possible to correlate changes in the 100 or 25 A porosity during irradiation with this accompanying turn-around. It is concluded therefore that such a correlation will occur with pores larger than approximately 100 A. Evidence is presented which suggests that the defect structure of different types of graphite becomes more nearly similar as a result of irradiation. (author)