The quick and ultrasensitive determination of K in NaI using inductively coupled plasma mass spectrometry

A highly sensitive, novel and quick assay method utilizing inductively coupled plasma mass spectrometry was developed for the determination of K in NaI powders and NaI(Tl) scintillator crystals for use in ultralow background applications. The determination of K (viz. 40K), as well as Th and U and their daughters, is important in ultralow background detector materials to ensure incorporation of materials of sufficiently high radiopurity. Through the use of improved instrumentation, cool plasma operating conditions, and meticulously clean sample preparations, detection limits of 11 fg natK g−1 (or 341 pBq 40K kg−1) was attained for K in pure water. Detection limits in the sample matrix (i.e., NaI) were 0.529 ng natK g NaI−1 (or 16.4 μBq 40K kg NaI−1). A number of different precursor NaI powder samples and NaI(Tl) scintillator crystals were assayed for their K content. Determinations ranged from 0.757 to 31.4 ng natK g NaI−1. This method allows for the screening of materials to unprecedented levels in a fraction of the time compared to gamma ray counting techniques, providing a useful method for a more effective screening tool of K in ultralow background detector materials.