Design and Operation of a Whole-body Monitoring System for the Goiania Radiation Accident

Abstract

With as many individuals involved in the Goiânia 137Cs accident who had high levels of internal contamination, it was necessary to improvise a whole-body counter installation in loco. The in-vivo counting system was located in a 4.0 X 3.5 X 3.5-m room, where seven layers of 2-mm lead sheets with dimensions of 2.0 m X 1.0 m were overlaid on the floor at loci that were equidistant from the walls. A 20-cm diameter NaI (Tl) detector was installed at a height of 2.05 m above the floor at the center of the room. The detector was shielded and collimated with 5 cm of lead. The enormous amounts of activity in the subjects required the detector to be positioned at a height of 2.05 m. Subjects were required to wear disposable clothing and lie on a reclining, fiberglass chair. Counting time for the subjects was 2 min (live-time). The minimum detectable 137Cs activity for this counting time was 7.3 kBq* (0.05 significance level). Besides the accident victims, all individuals who had direct or indirect contact with contaminated people or areas were also monitored. More than 300 people of both sexes, with ages varying from a few months to 72 y, were measured for whole-body radioactivity. The observed activities ranged from less than the minimum detectable activity (MDA) to 59 MBq.