Activity determination of 60Co and the importance of its beta spectrum

Karsten Kossert (1) , Justyna Marganiec-Galazka (1) , Xavier Mougeot (2) , Ole J. Naehle (1)

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

The activity concentration of a $^{60}$Co solution was measured by means of two 4$\pi\beta$-$\gamma$ coincidence counting systems using a liquid scintillation counter and a proportional counter (PC) in the beta channel, respectively. Additional liquid scintillation measurements were carried out and CIEMAT/NIST efficiency tracing as well as the triple-to double coincidence ratio (TDCR) methods were applied to analyse the data. The last two methods require computed beta spectra to determine the counting efficiencies. The results of both 4$\pi\beta$-$\gamma$ coincidence counting techniques are in very good agreement and yield a robust reference value. The initial activity concentration determined with liquid scintillation counting was found to be significantly lower than the results from 4$\pi\beta$-$\gamma$ a coincidence counting. In addition, the results from TDCR and CIEMAT/NIST show some inconsistency. The discrepancies were resolved by applying new beta spectrum calculations for the dominant allowed beta transition of $^{60}$Co. The use of calculations which take screening effects as well as the atomic exchange effect into account leads to good agreement between all four methods; the combination of these techniques delivers an important validation of beta spectra.

Keywords: Beta spectrum; CIEMAT/NIST efficiency tracing; TDCR; $^{60}$Co; Activity standardization; Coincidence counting

Domains: Physics [physics]; Nuclear Experiment [nucl-ex]

Karsten Kossert, Justyna Marganiec-Galazka, Xavier Mougeot, Ole J. Naehle. Activity determination of 60Co and the importance of its beta spectrum. Applied Radiation and Isotopes, 2018, 134 (SI), pp.212-218. ⟨10.1016/j.apradiso.2017.06.015⟩. ⟨cea-01799862⟩