Primary standardization of the massic activity of a 233Pa solution

Abstract

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.

Preparation and calibration of a 231Pa reference material

“…Preparation of the protactinium solutions, production of the reference material units, and characterization analyses are described in further detail below. Activity measurements performed for verification of the characterization analyses are described elsewhere [13][14][15] with results summarized here.…”

“…A primary 233 Pa massic activity measurement for the S solution was made by NIST using a live-timed 4πβ-γ anticoincidence counting method (LTAC) and confirmatory measurements were made by γspectrometry on efficiency-calibrated HPGe detectors. Details of the methods and data reduction for these analyses are provided in [13]. NRC also performed a primary calibration of S solution using an LTAC method and performed additional activity measurements using a CNET 3 H efficiency-traced liquid scintillation counting method and a Triple-to-Double Coincidence Ratio (TDCR) method [14].…”

“…This method avoids a laborious 233 Pa spike calibration but will typically have a relatively large uncertainty (> 2%, k = 2) due to the limits of neptunium assay measurements. More recently, Treinen et al [13] demonstrated the use of a characterized solution of high-purity 231 Pa as a reverse-spike for accurate and reproducible 233 Pa calibrations. This calibration was accomplished with less difficulty than rock standards and with uncertainties that are equivalent to, or lower than, those that can be reasonably obtained using activity measurements.…”