²³⁸U/²²⁶Ra or ²³²Th/²²⁸Ra: What is being measured in dietary items by gamma spectrometry?

^238U and ²³²Th and their decay radionuclides are naturally occurring radioactive materials (NORMs), existing in the earth's crust since its formation. Researchers undertake an assessment of radiation exposure to members of the public by conducting measurements to evaluate ²³⁸U and ²³²Th in several matrices. The assessment like an evaluation of annual effective dose from the consumption of vegetation and other dietary items should also be based ²²⁶Ra and ²²⁸Ra and not their parent radionuclides of ²³⁸U and ²³²Th. Therefore, when the indirect gamma spectrometry technique is used for the determination of NORM in dietary items, the following precautions should be taken