PRIMARY STANDARDIZATION OF THE MASSIC ACTIVITY OF A PROTACTINIUM-233 SOLUTION.

Protactinium-233 (233Pa) is used as a tracer for radiochemical analysis and is of particular interest as an isotope dilution mass spectrometry (IDMS) spike for 231Pa/235U radio-chronometry. To this end, we present massic activity determinations by two methods for a 233Pa solution, which was prepared at Lawrence Livermore National Laboratory (LLNL) and is being characterized at multiple labs as part of a 231Pa reference material production project. One activity determination method was 4πβ-γ anti-coincidence counting in a multi-dimensional extrapolation model, with Monte Carlo corrections. An independent massic activity determination was completed by γ-ray spectrometry using 5 HPGe detectors using 5 γ-ray lines. The anti-coincidence and γ-ray spectrometry results agree and have combined standard uncertainties of about 0.33 % and 1.0 % respectively. In addition, the two methods were combined to derive γ-ray emission probabilities from 233Pa decay.