Paramagnetic Resonance Absorption in Annealing Process of Radiation-Damaged Graphite

Abstract

An ESR study has been made of the isothermal annealing of radiation damage in a reactor-grade polycrystalline graphite after fast neutron bombardment at room temperature to total dose of 5.8×10²⁰ nvt. The absorption found for the specimens annealed below 950°C is concluded to be due to the unpaired electrons which as pointed out by Mrozowski are localized to the radiation-induced defects. On the other hand, for those annealed above 1450°C the Pauli-McClure type paramagnetism due to conduction carriers takes main part in ESR, while the localized spin centers still participate to some extent. In the annealing range between 1000°C and 1400°C no absorption signals have been observed, which is likely due not to the complete extinction of spin species but to the extreme broadening of line originating from some structural reasons.