An Extended Range Well Counter

A well-type detector is described for the assay of gamma emitters over a Curie-to-nanoCurie activity range. A large plastic scintillator/photomultiplier is DC-coupled for current measurements at high activities, with pulse counting covering the low activities. The two techniques overlap for two decades in the uCi region, particularly troublesome for the alternative detectors: gas-filled ionization chambers or NaI(Tl) well counters. The plastic well is interfaced to a microcomputer for data acquisition and control of the phototube high voltage, the key to the nine-decade dynamic range.