Standardized Annular Assay of Dual Radioisotopes on a Well Type Sodium Iodide Crystal

A procedure is described for the determination of the separate amounts of two gamma-emitting radioisotopes present simultaneously in large liquid volumes using an annular cell placed over a standard well-type crystal of sodium iodide and a reference source of (137)Cs. This sensitive technique is illustrated with particular reference to the double radioisotope urinary excretion test, using orally administered (57)CoB(12) bound to human gastric juice and (58)CoB(12) simultaneously, for the differentiation between patients with intrinsic factor deficiency and other causes of vitamin B(12) malabsorption.