THE MEASUREMENT OF INCORPORATED RADIOACTIVE ACTINIDES IN THE BODY BY DIRECT-METHODS

From the beginning of the nuclear industry the assessment of incorpora ted radionuclides has been an absolute necessity. Although this assess ment is easy for many nuclides (fission or activation products, etc.), the problem of the detection and quantification of some of the actini des is still a challenge. Several of these, e.g. uranium, are easy to detect, but thorium, americium and plutonium are very difficult to ass ess. The necessity for the quantification of these elements is dictate d by new recommendations of the International Commission for Radiologi cal Protection which propose lower Annual Limit of Intake values, ofte n less than the detection limits of the present measurement systems (p roportional counters and ''Phoswich'' scintillators). The new technolo gies are based on semiconductor detectors with large detection areas. Presently HPGe detectors are most appropriate for this application, bu t surface barrier detectors or room temperature systems (CdTe, HgI2) a re being investigated. This paper describes the state of the art and t he trends of Belgian Nuclear Research Centre in this field. Some examp les of measurements are given.