A gamma-ray counter for liquid or solid samples is described. It uses an RCA 5819 phototube at room temperature with a thallium activated sodium iodide crystal in the shape of an annular ring. The gamma-ray counting efficiencies of this counter for 2-milliliter samples of Fe59, Co60, and I131 are about equal to the beta-particle counting efficiency of a mica-window G-M counter when counting thin samples. When the counter is heavily shielded, the background is about 160 counts per minute. The phototube operating voltage is not critical since over a wide range of operating voltage the counting efficiency and background count change only slightly. A directional gamma-ray counter is also described.
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Hal O. Anger (1951) studied this question.