Speaker
Description
Authors (affiliation): Denis E. Bergeron 1, Jeffrey T. Cessna 1, Ryan P. Fitzgerald 1, Lizbeth Laureano-Pérez 1, Leticia Pibida 1, Brian E. Zimmerman 1
(1 NIST, USA)
Gadolinium-153 decays 100 % by electron capture to several excited levels of Eu-153.Applications in nuclear medicine and in gamma-ray spectrometry calibrations require improved nuclear decay data for Gd-153.Several studies have now established that the exact electron capture branching is uncertain, with discrepant data evaluations estimating anywhere from 0 % to 4 % probability for electron capture directly to the Eu-153 ground state (i.e., the ϵ0,0 transition).
NIST recently measured a solution of 153GdCl3 in HCl by live-timed 4πβ(LS)-γ(NaI(Tl)) anticoincidence counting (LTAC) and submitted an ampoule to the International Reference System (SIR) as part of the BIPM comparison BIPM.RI(II)-K1.Gd-153[1]. As part of this measurement campaign, gravimetrically-related sources were measured by liquid scintillation counting, including triple-to-double coincidence ratio (TDCR) counting, providing a set of LTAC-based empirical LS efficiencies against which calculated efficiencies could be benchmarked. Calculated TDCR efficiencies are particularly sensitive to the adopted electron capture branching scheme and the experimental data are clearly more consistent with a scheme that excludes the ϵ0,0 transition.
Linked sources were measured with calibrated HPGe and Si(Li) detectors to determine absolute emission intensities for the main γ rays (Iγ). These results were generally consistent with the recent report from Shearman et al. [2] and support a decay scheme without the ϵ0,0 transition.For the 97.4 keV γ ray, we found Iγ = 0.3022(24), consistent with Shearman and approximately 3.4 % higher than the DDEP evaluated value. For the 69.7 keV γ ray, we found Iγ = 0.0255(4), significantly higher than previous reports. Finally, new half-life measurements were acquired over up to 3 half-lives with ionization chambers, a well-type NaI(Tl) detector, and a HPGe detector.
[1] C. Michotte et al., Metrologia, 58, 06027 (2021).
[2] R. Shearman et al., EPJ Web of Conferences,146, 10008 (2017).
