Improved protactinium spike calibration method applied to 231Pa-235U age-dating of certified reference materials for nuclear forensics.

The application of multiple radiochronometers in a forensic investigation of bulk uranium provides increased confidence for interpreting age-dating results. We have developed a streamlined method for the purification of Pa and Th from bulk uranium and have applied this method in analyzing uranium certified reference materials (CRMs) IRMM-1000 and CRM U100, using the ²³¹Pa-²³⁵U and ²³⁰Th-²³⁴U radiochronometers. Our improved ²³³Pa spike calibration technique has replaced the time-intensive, conventional calibration using geologic rock standards. Paired Pa-U and Th-U age-dating analyses of CRM U100 produce concordant results. In contrast, analyses of IRMM-1000 demonstrate reproducibly-discordant Th-U and Pa-U age-dates. [ABSTRACT FROM AUTHOR]