In-Vivo Calibration of a LE Ge detection system for the assessment of Americium in bone, in the Whole Body Counter of CIEMAT

The calibration of a LE Ge detector system has been performed at CIEMAT Whole Body Counter for the assessment of Am in skull and knee. The facility counts with a Cohen phantom simulating a human head with 1000 Bq of Americium homogeneously distributed in the bone equivalent material. Measurements of the LE Ge system with the skull phantom were carried out in an optimisation study of counting efficiency for Am determination. A Monte Carlo approach was also applied and the mathematical efficiencies were compared with experimental measurements, showing a bias less than 10% at a short detector-skull distance. A Spitz knee phantom simulating internal contamination of Americium in bone was counted for calibration purposes using two LE Ge detectors; the efficiencies obtained for each pair of detectors were used to calculate the Activity contained in the IAEA knee phantom received at CIEMAT during an In-Vivo Intercomparison. A new calibration was performed using the four LE Ge detectors and two knee phantoms. The efficiency obtained with the LE Ge detection system measuring Americium in two knees showed a lower value comparing with skull efficiencies for 59.5 keV emissions. As knee counting geometry was proved to be more comfortable for the subject, an optimisation study of knee counting efficiency will be considered in the future.