DIRECT BETA-MEASUREMENT TO DETERMINE IN-VIVO WHOLE-BODY ACTIVITIES OFSR-90 IN RESIDENTS OF THE SOUTHERN URALS - DESCRIPTION OF A NEW METHOD

For 44 individuals living in areas of the Southern Urals with historic al Sr-90 contamination, whole-body activities of this radionuclide wer e investigated using a new mobile detection system. beta-particles fro m Sr-90/Y-90 decay were measured in vivo via two proportional counters mounted in front of the forehead and above the head, respectively. In order to correct for absorption by the skin, scalp thickness was meas ured using ultrasonic techniques. Corrections are given with respect t o self-absorption by the bone matrix and absorption by hair. A procedu re is described to extrapolate from measured Sr-90 activity of the sku ll bone to total Sr-90 skeleton burden. As a result, Sr-90 whole-body activities of up to 50 kBq were recorded in the selected cohort. For t he same individuals, Sr-90 was measured via the detection of bremsstra hlung using an established whole-body counting device. The overall res ults of both systems agree within 15%, but differences exceeding a fac tor of 2 were observed in some cases.