In-vivo counting of 241Am in human lungs and tracheobronchial lymph nodes

A study was conducted of a human male who had inhaled a mixture of 241Am and Pu. To distinguish 241Am deposited in the subject's lungs from translocated activity deposited in the tracheobronchial lymph nodes (TBLN), two intrinsic Ge detectors were collimated with 0.3-cm Pb sheeting. A tissue-equivalent phantom containing either 22.9 kBq (620 nCi) of 241Am in the lungs or a 81.4 kBq (2200 nCi) 241Am point source in the TBLN was measured. Calibration curves observed from lateral differential scans on the phantom were compared to data obtained by the same detection system for a human male with a measured lung deposition of 89 Bq (2.4 nCi) of 241Am. Comparison of the human data to the calibration curves indicated the activity was restricted primarily to the lungs. The calibration curves demonstrate that this method is useful in determining the distribution of inhaled radioactivity between the lungs and TBLN. The measured activity from the male subject generally supported the ICRP Publication 30 model translocation prediction for class Y compounds.