| Summary: | A scintillation counter for the measurement of extremely low specific beta activities has been developed which achieves its high sensitivity through the application of large amounts of radioactive substance, and the use of an efficient liquid scintillation phosphor. The counter can be used in two different ways; as a volume counter and as a multiple-sample counter. In the first type of counter the solid radioactive sample is mixed with the liquid phosphor to form a transparent paste; in the second type a smaller amount of solid sample is spread out on a large surface of cellophane and immersed in the scintillating fluid.
Experiments have been made with K⁴⁰ , C¹⁴ , and S³⁵ to determine the range of application, sensitivity, and efficiency of the counters. The volume counter can be used to assay a wide variety of material and is especially suited for biological problems. Its sensitivity was found to be better than 10⁻¹¹ curies/gm., while that of the multiple-sample counter is of the order of 10⁻¹⁰ curies/gm.. These sensitivities can be measured with a good degree of reproducibility and are superior to the conventional methods, with the exception of the elaborate screen-wall counter method. === Science, Faculty of === Physics and Astronomy, Department of === Graduate
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