Calibration of a new spectrometry setup for in-vivo lung monitoring

In lung monitoring, the objective is to screen if plutonium has been inhaled from the people and, to do this, 241Am peak energy (59 keV) is searched by using three germanium detectors, which are chosen for their high resolution, especially at low energy. To increase the measurement efficiency a new set of bigger Germaniun detectors were mounted in the SCK-CEN anthropogammametry laboratory. The objective of this study is to calibrate and optimize this new setup for in-vivo lung monitoring based on a system of three new HPGe (High Purity Germanium) detectors. Finding the best position of the detectors and evaluating the measurements uncertainties will lead to an improvement of the detection efficiency which automatically reduce the MDA (Minimum Detectable Activity) that can be detected in the worker lungs. The Monte Carlo code will be the tool to find the measurement position in order to reach the best efficiency of the detectors. For the calibration of the detectors, a physical phantom (Livermore Lawrence National Laboratory phantom) will be used. Because the efficiency changes a lot with the thickness of the chest at low energy (range of our interest), this phantom is provided with four overlays of different Chest Wall Thickness (CWT). After doing the measurements with this phantom, different efficiency curves depending on the CWT will be obtained. They will be implemented in the used software (Genie2000) and in this way, when a person arrives for his measurement, it will be possible to choose the suitable curve, depending on its CWT. Also efficiency uncertainties analysis will be done, because there will be several parameters that could affect the reliability of the measurements, like the movements of the people during the measurements. MCNP will be also used for studies about the efficiency differences that can be present changing some parameters, like distance between detectors and torso and lungs size.