Measurement of naturally occurring radioactive materials, ²³⁸U and ²³²Th. Anomalies in photopeak selection

There are more than 200 photopeaks of various daughter radionuclides of ²³⁸U and ²³²Th series, some of which have been randomly used for quantitative measurement of U/Th in natural samples. It has been observed that arbitrariness in photopeak selection may fail to stipulate statistically consistent data. This paper judiciously selects set of three photopeaks from each series whose respective averages could present statistically reliable measurement of ²³⁸U and ²³²Th based on minimum relative standard deviation (RSD) under the selected photopeaks. RSD is also proposed as an important parameter in NORM measurement. (author)