A PARTIAL BODY COUNTER FOR INCORPORATED LOW-LEVEL ACTINIDES

A new partial body counter has been installed and calibrated at the In stitute of Radiation Hygiene of the Federal Office for Radiation Prote ction, Munich, Bavaria the system is especially designed for radionucl ides emitting low energy photons such as Am-241 and Pb-210. In additio n, thorium, uranium and daughter products, Co-60, Cs-137 and K-40 can be detected. The main components of the system am a shielding chamber, 4 high purity low-energy germanium detectors with beryllium windows a nd the corresponding electronics and software. A LLNL Realistic Phanto m is used to calibrate the system. Inactive organs and organs loaded w ith a known amount of Am-241 (right lung, left lung, liver) are availa ble to quantify the response of each detector separately. Detector eff iciencies are given as Function of chest wall thickness (1.7 to 3.4 an ). Lower limits of detection for Am-241 using a measurement time of 36 00 seconds are 6, 7 and 7 Bq for night lung, left lung and liver, resp ectively. In order to estimate skeleton activities, a skull phantom lo aded with Am-241 is available. For one detector, the lower limit of de tection for the skull is 2 Bq.