Activity standardization of two enriched 40K solutions for the determination of decay scheme parameters and the half-life

Karsten Kossert (1) , Yuri Amelin (2) , Dirk Arnold (1) , Renaud Merle (2, 3, 4) , Xavier Mougeot (5) , Michael Schmiedel (1) , Daniel Zapata Garcia (1)

1 PTB - Physikalisch-Technische Bundesanstalt [Braunschweig]
2 ANU - Australian National University
3 NRM - Swedish Museum of Natural History
4 Uppsala University
5 LNHB (CEA, LIST) - Laboratoire National Henri Becquerel (CEA, LIST)

In this paper we describe experiments on two enriched 40K solutions to accurately determine decay data. The first solution was measured in 2004/2005 by means of a gamma-ray spectrometer with low background and a liquid scintillation (LS) counter to apply the CIEMAT/NIST efficiency tracing method. A combination of results yields an emission probability of the 1461 keV gamma-rays of Pg=0.1030(11) which is lower than current results of data evaluations. The activity concentration of the second solution was also determined by means of LS counting, but here, the CIEMAT/NIST efficiency tracing method as well as the TDCR method were applied. Again, the result was combined with that of independent gamma-ray spectrometry and the gamma-ray emission probability was found to be Pg=0.1029(9) in good agreement with the result obtained from the first solution. A combination of both experiments yields Pg=0.1029(9). The spectra of a TriCarb LS counter were carefully analyzed and a beta minus emission probability Pb- =0.8954(14) was determined. The new results for Pg and Pb- indicate that the overall probability of the decay via electron capture in recent data evaluations is overestimated. The LS counting efficiencies were computed with a stochastic model and up-to-date calculations of the beta spectrum and fractional electron-capture probabilities were used. The final activity result of the second solution is combined with the outcome of a comprehensive isotopic analysis to determine the half-life of 40K which is found to be 1.2536(27) 10^9 years.

Mots clés: 40K; activity standardization; liquid scintillation counting; TDCR; CIEMAT/NIST efficiency tracing; branching ratio; metrology; ionizing radiation; radioactivity; spectrometry; Decay data measurement; gamma spectrometry; beta-rays

Domaines: Physique Nucléaire Expérimentale [nucl-ex]

Karsten Kossert, Yuri Amelin, Dirk Arnold, Renaud Merle, Xavier Mougeot, et al.. Activity standardization of two enriched 40K solutions for the determination of decay scheme parameters and the half-life. Applied Radiation and Isotopes, 2022, 188, pp.110362. ⟨10.1016/j.apradiso.2022.110362⟩. ⟨cea-03736184⟩