Where uranium and thorium are in secular equilibrium with their decay products, these elements may be determined by this direct radiometric method if the materials show more than 0.01 per cent equivalent uranium. This method is based on the measurement in a scintillation spectrometer of the relative amplitude of the response from the 238 kev gamma ray from Pb212. Tests on known samples containing different relative proportions of uranium and thorium have verified the predicted precision of better than 4 per cent standard deviation per single comparison with a standard when the element measured is a major contributor to the activity.

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