A STUDY OF THE EMANATION METHOD FOR THE DETERMINATION OF THE SURFACE AREA OF THORIUM OXIDE

The surface areas of several thorium oxide and thorium oxide--uranium oxide preparations were measured by the emanation method. The radioactive gas- counting system employed is described, and a discussion of the procedure for converting counting data to terms of emanating power and finally to surface area values is given. Surface area values by the emanation method were compared with BET values from like samples. The difference between values obtained by the two methods was attributed to the efficiency of the radioactive gas-detecting system and the porosity of the oxide samples. The contribution of Rn/sup 2//sup 2//sup 2/ from the oxide samples containing uranium was found to be negligible and presented no problem. Samples fired at temperatures above 1500%DEC for one hour in air exhibited a marked increase in "room temperature" emanation rates. The predicted lattice-loosening temperature of metal oxides is approximately one-half their absolute melting point. Above this temperature, sufficient thermal agitation is induced to permit exchange and possibly permanent displacement of atoms in the crystal lattice. Therefore, firing these oxide preparations at temperatures above 1500 deg C would probably result in lattice defects throughout the crystal structure, with the surface defects contributing to an increase in surface area and a corresponding increase in the emanation rate. (auth