Quantitative Compton suppression spectrometry at elevated counting rates

For quantitative Compton suppression spectrometry the decrease of coinciden ce efficiency with counting rate should be made negligible to avoid a virtu al increase of relative peak areas of coincident isomeric transitions with counting rate. To that aim, a separate amplifier and discriminator has been used for each of the eight segments of the active shield of a new well-typ e Compton suppression spectrometer, together with an optimized, minimum dea d-time design of the anticoincidence logic circuitry. Chance coincidence lo sses in the Compton suppression spectrometer are corrected instrumentally b y comparing the chance coincidence rate to the counting rate of the germani um detector in a pulse-counting Busy circuit (G.P. Westphal, J. Rad. Chem. 179 (1994) 55) which is combined with the spectrometer's LFC counting loss correction system. The normally not observable chance coincidence rate is r econstructed from the rates of germanium detector and scintillation detecto r in an auxiliary coincidence unit, after the destruction of true coinciden ce by delaying one of the coincidence partners. Quantitative system respons e has been tested in two-source measurements with a fixed reference source of Co-60 Of 14 kc/s, and various samples of Cs-137, UP to aggregate countin g rates of 180 kc/s for the well-type detector, and more than 1400 kc/s for the EGO shield. In these measurements, the net peak areas of the 1173.3 ke V line of 60Co remained constant at typical values of 37 000 with and 95 00 0 without Compton suppression, with maximum deviations from the average of less than 1.5%. (C) 1999 Elsevier Science B.V. All rights reserved.