Intercalibration of in vivo counting systems using an Asian phantom. Results of a co-ordinated research project 1996-1998

Radioactive materials are used in many industries, and, whenever unsealed radioactive sources are present, intakes of radionuclides by workers can occur. Adequate radiation protection of workers is an essential requirement for the safe and acceptable use of radiation, radioactive materials and nuclear energy. Guidance on the application of the requirements of the International Basis Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources (BSS) to occupational protection is given in three interrelated Safety Guides: Occupational Radiation Protection (RS-G-1.1); Assessment of Occupational Exposure due to Intakes of Radionuclides (RS-G-1.2); Assessment of Occupational Exposure due to External Sources of Radiation (RS-G-1.3) published in 1999 and further guidance is given in Safety Reports. Uranium, thorium and transuranic elements such as plutonium and americium are encountered throughout the nuclear fuel cycle and in industry. Radionuclides of these elements have a significant potential for internal radiation exposures when they are ingested or inhaled. As a result, the dosimetry services responsible for internal dose assessment must be capable of detecting such radionuclides deposited in the body in very low quantities. The detection problem is made more difficult because several of these radionuclides (e.g. 238,239Pu, 241Am, and 235U) decay with the emission of low energy photons that are difficult to detect by direct measurement or in vivo methods. A variety of sophisticated detection systems has been developed to address this problem. In addition, complex anthropomorphic phantoms have been fabricated to provide for highly realistic detector calibrations. However, the measurement task remains highly challenging. The detection and calibration resources are costly, and relatively few dosimetry services are equipped to undertake these measurement tasks. This report describes the development of international programmes conducted by the IAEA involving the use of torso phantoms which facilitated the calibration and comparison of national detection systems. More specifically, it describes the use of the so-called Asian Phantom for intercalibrating in vivo counting systems