A65Zn solution was standardized by the 4πPC-γ efficiency-extrapolation coincidence counting method. Theoretical aspects of coincidence equations, efficiency equations and linearity conditions are reviewed. Experimental measurements were performed for two low level discrimination thresholds for the PC channel (counting K+L or K X-rays or Auger electrons from EC decay) and for three different settings of the γ window. Requirements on γ channel set-up for linear extrapolation were established by using a Pb absorber or by proper γ window setting. The measured activity values were discussed and found in good agreement with those obtained with a calibrated ionization chamber. © 2003 Elsevier Ltd. All rights reserved.
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