QUANTITATIVE-ANALYSIS OF FATE IN MAN OF AR-37 PRODUCED IN BODY CALCIUM BY FAST-NEUTRON EXPOSURE

Methods were developed to investigate the quantitative production and the ultimate fate of 37Ar produced in bone Ca in the living human body. A healthy male subject''s whole body was irradiated using cyclotron-produced neutrons provided by the 9Be(3He, n) reaction. The dose of fast neutrons was limited to 1.6 mrad. Six breath samples were collected and assayed for 37Ar content over a 12.5 h period after irradiation. Low background (0.5-5 counts/day) gas proportional counting techniques were used to assay samples containing as little activity as 0.01 dpm corrected to end of irradiation. Analysis of the exhalation data by a 2-component exponential relation indicated 82% of the activity left the body by way of the lungs with a half-time of 40 min. The remaining 18% was exhaled with a 200 min half-time. Exhalation was demonstrated to account for approximately 70% of the 37Ar activity produced in the body. Evidence from studies of isolated bone indicated that essentially permanent trapping in bone crystals accounted for the remaining activity.