The standardization of 33P by the TDCR efficiency calculation technique

The activity of the pure beta-emitter phosphorus-33 (33P) has been directly determined by the triple-to-double coincidence ratio (TDCR) efficiency calculation technique, thus extending the number of radionuclides that have been standardized by this simple, non-extrapolation liquid scintillation (LS) method. The major advantage of inherently accounting for chemical quenching without the need for additional external measurements is demonstrated. The 33P solution activity concentration was verified by tracing with cobalt-60, utilizing 4π(LS)β–γ coincidence counting. Agreement to within 1.2% confirmed the reliability of the TDCR measurements.