The measurement of incorporated radioactive actinides in the body by direct methods

From the beginning of the nuclear industry the assessment of incorporated radionuclides has been an absolute necessity. Although this assessment is easy for many nuclides (fission or activation products, etc.), the problem of the detection and quantification of some of the actinides is still a challenge. Several of these, e.g. uranium, are easy to detect, but thorium, americium and plutonium are very difficult to assess. The necessity for the quantification of these elements is dictated by new recommendations of the International Commission for Radiological Protection which propose lower Annual Limit of Intake values, often less than the detection limits of the present measurement systems (proportional counters and "Phoswich" scintillators). The new technologies are based on semiconductor detectors with large detection areas. Presently HPGe detectors are most appropriate for this application, but surface barrier detectors or room temperature systems (CdTe, HgI₂) are being investigated. This paper describes the state of the art and the trends of Belgian Nuclear Research Centre in this field. Some examples of measurements are given.