Springer Online Journal Archives 1860-2000
Summary A human total-body counter was designed and built with two 20 × 10 cm NaI (Tl) crystals suspended over an “isoresponse surface” upon which the subject reclines. This surface is curved from head to knee and from left to right, so that a gamma-ray emitting object is detected with equal efficiency when placed anywhere upon it. The positioner and detectors are housed in a low background enclosure constructed of steel 31 cm thick with a graded inner lining of lead + cadmium + copper. Calibration of the system was accomplished by administering trace amounts of various radionuclides to 48 human subjects of various sizes, ranging in age from 4–80 years. Counting rates per retained μCi at 0.53, 0.66, 1.53, and 2.75 MeV (83Rb,137Cs,42K, and24Na) were determined as a function of body size and were compared with counting rates per μCi of corresponding emitters centered in a polyethylene cylinder of radius 10.3 cm. Limits of detection, corresponding to three times the standard deviation of a 50 min background, were 170 nCi90Sr (via Bremsstrahlung X-rays), 0.78 nCi131I, 0.48 nCi83Rb, 0.52 nCi137Cs, 4.9 nCi40K (or 5.8 g of natural potassium), and 1.7 nCi222Rn.
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