Annealing effects on Galvanomagnetic Properties of Heavily Radiation-Damaged Graphite

An annealing study of radiation-damage in graphite has been made through the observation of the changes in electrical resistivity, Hall coefficient and magnetoresistance at room and liquid-nitrogen temperatures. The specimen examined is a pile-grade polycrystalline graphite bombarded with fast neutrons at 30°C to total dose of 5.8×10 20 nvt. The isothermal annealing is performed in a stepwise manner at temperatures from 200°C up to 2400°C. The recovery diagrams are characterized by the presence of two major stages lying on the annealing temperature axis; the relatively small one around 300°C and the bigger around 1300°C. Based on a parabolic two-band representation for the electronic structure, thorough analyses are made of the whole data, which lead to a coherent description of the recovery process in terms of the following parameters; the density and mobility of conduction carriers, the overlap of upper and lower bands and the location of the Fermi level. Discussions are also given in relation to the defect structure.