The surface areas of several thorium oxide and tho¬rium 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 are compared with BET values from like samples. The difference between values obtained by the two methods is attributed to the efficiency of the radioactive gas-detecting system and the porosity of the oxide samples. The contribution of Rn222 from the oxide samples containing uranium was found to be negligible and presented no problem.
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