Natural radioactivity found in bioassay measurements

The internal radiation exposure of occupationally exposed persons in nuclear facilities is checked regularly for internal contamination by bioassay measurements. Although these persons are generally not involved in any incident, natural radioactivity from U, Th and Ra can be found in their urine or faeces. Uranium has been found with no particular ratio between ²³⁴U and ²³⁸U. ²³⁰Th, ²²⁸Th and sometimes ²³²Th have also been detected. ²²⁸Th has generally been found in excess of ²³²Th. All these measurements were performed by alpha spectrometry. The few ²²⁶Ra results have been measured using the Lucas or emanation method.