Studies in the Design and Applications of a Clinical Low Background Counting Room

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Abstract
An account is given of the construction and use of a comparatively inexpensive whole-body counting room, designed primarily for clinical application. Bulk shielding is provided by about 16 tons of chalk, loaded into polythene-lined paper bags, to form a layer 2 ft. thick, the room being lined inside with 0.25 thick aged lead sheets. Comparative studies of the background of scintillation counters in this room, and in other shielded rooms, are presented; it is noted that for gamma energies> 250 keV the background was reduced from 50 to 4.2 cps when a particular counter was taken from a brick-walled laboratory into the chalk-bag shielded room, but only by a further 2.6 cps if instead the counter was shielded by 4 in. of lead. Illustrations of clinical applications of the room are given these, using three 3 in. diameter X 2 in. long Nal (TI) crystals as detectors, including studies of the retention and redistribution of 47ca following the administration of about 1 uc of this nuclide, and measurements of the retention of 131I several weeks after therapeutic administration to patients. Examples are also given of measurement of low-level contamination due to the administration of Thorotrast, and to the ingestion of 131I from radioactive fallout during a period of nuclear weapon tests.