Improved activity standardization of $^{90}$Sr/$^{90}$Y by means of liquid scintillation counting

Karsten Kossert (1) , Xavier Mougeot (2)

1 PTB - Physikalisch-Technische Bundesanstalt [Braunschweig]
2 LNHB - Laboratoire National Henri Becquerel

Radioactive strontium isotopes play an important role in environmental radioactivity. Reliable activity standards are required in order to validate radioanalytical techniques and related measurements. In this paper, improved methods for the primary activity standardization of $^{90}$Sr/$^{90}$Y based on liquid scintillation counting are presented. To this end, two methods were used: the CIEMAT/NIST efficiency tracing technique with 3H as a tracer and the triple-to-double coincidence ratio method. Non-negligible discrepancies between the two methods were found when applying existing analysis techniques. A detailed study was carried out to identify and eliminate the causes of these discrepancies. Eventually, excellent agreement between the two methods was obtained. This required advanced beta spectrum calculations which were carried out with a specific version of the BetaShape program taking the atomic exchange effect into account. In addition, it was found that the quench-indicating parameters determined in commercial liquid scintillation counters are biased, which can cause significant problems for the CIEMAT/NIST efficiency tracing method. The effect depends on the counting rate and can be explained by a superposition of the LS spectra generated by $^{90}$Sr/$^{90}$Y and the external standard source.

Keywords: 90Sr/90Y; strontium isotopes; Activity standardization; activity standards; primary activity standardization; primary activity measurement; Beta spectrum shapes; beta spectrum; Liquid scintillation counting; liquid scintillator; metrology; ionizing radiation; Radioactivity; calibration; CIEMAT/NIST efficiency tracing; tritium tracer; triple-to-double coincidence ratio method

Domains: Nuclear Theory [nucl-th]; Nuclear Experiment [nucl-ex]

Karsten Kossert, Xavier Mougeot. Improved activity standardization of $^{90}$Sr/$^{90}$Y by means of liquid scintillation counting. Applied Radiation and Isotopes, 2021, 168, pp.109478. ⟨10.1016/j.apradiso.2020.109478⟩. ⟨cea-03136319⟩