Preparation and standardization of 229Th SRM 4328d

The certified massic activity for 229Th in SRM 4328d was obtained by 4παβ liquid scintillation (LS) counting by comparative measurements in 2022 against SRM 4328c. Both SRMs were prepared from the identical 2007 229Th stock solution. SRM 4328c was standardized in 2007 by live-timed anticoincidence counting (a primary standardization method) with confirmatory measurements by four other methods. The comparative measurements were performed using two different commercial LS counters and with LS counting sources prepared with two different cocktail compositions. Homogeneity of SRM 4328d was confirmed by photonic emission spectrometry of the SRM ampoules with a NaI(Tl) well counter. The certified massic activity of 229Th in SRM 4328d, based on the decay-corrected certified value for SRM 4328c, is (41.19 ± 0.41) Bq·g-1 at k = 2 as of 1200 EST, 14 July 2022. This report documents the preparation, standardization, and certification of SRM 4328d.