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 ~15% smaller than that for the old lung counter. Minimum detectable activities (MDAs) for 241Am and 239Pu 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 241Am and 239Pu 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.