Abstract
The Hahn's emanation technique using the escaping tendency of 54.5-second thoron has been applied to the following studies: (1) the effect of calcination temperature on the specific surface area of thorium dioxide prepared from the oxalate, and (2) activation energies for the diffusion of thoron in thorium dioxides prerared from oxalate, hydrous oxide and oxycarbonate by firing at 1050°C. The measured emanation activity was simply assumed to be composed of the recoil fraction and diffusion fraction.
The room-temperature emanation activity, which can be taken as being equal to the recoil fraction and being proportional to the specific surface area, decreased with increasing calcination temperature, and it corresponded well to the decrease in the measured specific surface area and the rate of absorbing water vapor.
From the Arrhenius plots of the diffusion fraction which was obtained by substraction of the roomtemperature emanation activity from the measured activity at each temperature, activation energies for the diffusion of thoron in thorium dioxide were determined. Depending on the temperature and the source of the oxide, different activation energy processes could be attributed to the various diffusion processes.
