Standardization of 68(Ge+Ga)

The radionuclide 68 Ga is mainly a positron emitter (89.2%), with a half-life of 67.7 min. It is used in nuclear medicine, being chemically extracted from the mixture 68 (Ge+Ga); its precursor, 68 Ge, disintegrates 100% by electron capture, with a half-life of 270.8 d (Table of radionuclides, comments and Evaluation). A 4 πβ – γ coincidence method was used for standardization, with a 4 π proportional β -detector and a NaI(Tl) γ detector. Registration of the capture radiations was avoided using foil absorption and a high β threshold. Using supplementary foils for positron absorption, extrapolation graphs were obtained, with a mean slope of −4.4%. Care was taken to compensate for the loss of 68 Ge during the preparation of solid sources for measurement. A combined uncertainty of 1.1% was estimated.