A performance comparison study between two HPGe lung counters with different detector configurations

This study compares the performance of old and new lung counters in the National Institutes for Quantum Sciences and Technology of Japan. The total sensitive area of the detector crystals for the new lung counter is similar to 15% smaller than that for the old lung counter. Minimum detectable activities (MDAs) for Am-241 and Pu-239 were evaluated through experiments using a Lawrence Livermore National Laboratory torso phantom. Despite differences in detector configuration, the MDAs were found to be comparable between the two lung counters. For a chest wall thickness of 2.1 cm and a counting time of 30 min, the MDAs of Am-241 and Pu-239 were 5.7 and 2300 Bq for the old lung counter, and 5.5 and 2600 Bq for the new lung counter, respectively. Experimental results for the relative sensitivities between left-side and right-side detectors suggested that the new lung counter offered better measurement geometry.