PRACTICAL ASPECTS OF LABORATORY SCINTILLATION COUNTING

Journal/Book: Reprinted from THE JOURNAL OF LABORATORY AND CLINICAL MEDICINE St. Louis. Vol. 40 No. 4 Pages 641-648. October 1952. 1952;

Abstract: RAYMOND L. LIBBY PH.D. CHRISTINE M. TAYLOR AND PANCHITA B. THOMAS LOS ANGELES CALIF. From the Radioisotope Laboratory Wadsworth General Hospital Veterans Administration Center and the Department of Radiology School of Medicine University of California. Reviewed in the Veterans Administration and published with the approval of the Chief Medical Director. The statements and conclusions of the authors are the results of their own study and do not necessarily reflect the opinion or policy of the Veterans Administration. Received for publication June 23 1952. *The complete unit for gamma counting (excluding crystal) can be obtained from the Radio Biological Apparatus Company Berkeley 2 Calif. The holder for the stilbene crystal was fabricated in the radioisotope laboratory. The phosphors may be obtained from a number of sources such as Tracerlab Harshaw Chemical and National Radiac Companies. THE physical characteristics of various phosphorus photomultiplier tubes and circuits suitable for scintillation counting have been covered in considerable detail in the literature in the last few years.1-3 Reports have also appeared from this laboratory and others an the clinical application of scintillation counters in the determination of I131 "uptake" by the thyroid gland for obtaining in vivo scintillation of radioactive areas etc.4-7 However relatively little has been published concerning the practical details involved in performing radio-assays in the laboratory with a scintillation counter used as the radiation detector. It is the purpose of this report to present in some detail the scintillation counter techniques employed in this laboratory for the detection of beta particle and gamma ray radiation. EQUIPMENT A thallium-activated sodium iodide [NaI(TI)] phosphor 4.3 cm. in diameter by 1.8 cm thick is used as the scintillating crystal for the detection of gamma radiation and a stilbene crystal of similar dimensions for beta particle counting. These crystal phosphors are mounted in an aluminum holder fitted at one end with a screw-an Lucite cap fitted with a rubber gasket (Fig. 1 a). The outer surface of this Lucite cap is machined and polished to correspond to the photocathode end of an RCA 5819 multiplier phototube. The window end of the aluminum holder for the NaI(TI) crystal is milled so that the aluminum window is approximately 0.1 millimeter in thickness. The window end of the stilbene crystal holder consists of one or two layers of black paper held in position by a spring clip. The aluminum crystal holder is threaded so that it may be screwed into a brass tube 25 cm. long by 6 cm. in diameter (Fig. 1 b). Fig. 1 c shows the 5819 photomultiplier tube and built-in preamplifier which likewise fits into the brass tube.* ___MH

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