The Liquid Scintillation Counting Process. The Gamma Counting Process

Abstract

H.P. Kallman, using crystals of naphthalene, showed that the crystals could be used to detect alpha, beta, and gamma radiation, and that certain substances like naphthalene, if dissolved in aromatic solvents, were excellent scintillation sources when subjected to nuclear radiations. 1 Liquid scintillation counting, though, owes its origin to the discoveries of Reynolds, 2 Kallman, 3 and Ageno 4 who, in 1950, independently showed that certain organic solutions fluoresce noticeably when bombarded with radiation. Shortly after these demonstrations, the potential of liquid scintillation counting was recognized by many. The rapid development of efficient scintillation solutions and of the coincidence liquid scintillation counter opened the entire fields of nuclear biology and radiopharmacology to the use of the tracer technique. Prior to this, the weak beta emitters of tritium and 14C were very difficult to count. Carbon-14 was counted as solid BaCO3 on planchets or as gaseous CO2 in ionization chambers. Tritium was next to impossible to count except as a gas. The unique feature of modern liquid scintillation counting is that the radioactive sample and the scintillation solution are intimately mixed, usually in a homogeneous solution that permits 4π geometry for radiation detection. This internal sample technique has led to greatly increased sensitivities for the measurement of all low-energy beta emitters, especially tritium and 14C. Modern liquid scintillation solutions, advanced sample preparation techniques, and superb liquid scintillation counters have expanded the realizations of liquid scintillation counting far beyond the most optimistic dreams of early investigators in the field.