Precision measurement of $^{65}$Zn electron-capture decays with the KDK coincidence setup

L. Hariasz, P. C. F. Di Stefano, M. Stukel, B. C. Rasco, K. P. Rykaczewski, N. T. Brewer, R. K. Grzywacz, E. D. Lukosi, D. W. Stracener, M. Mancuso, F. Petricca, J. Ninkovic, P. Lechner
Nuclear Experiment, Nuclear Experiment (nucl-ex)
Nuclear Data Sheets 189-224 (2023)
2023-08-07 16:00:00
$^{65}$Zn is a common calibration source, moreover used as a radioactive tracer in medical and biological studies. In many cases, $\gamma$-spectroscopy is a preferred method of $^{65}$Zn standardization, which relies directly on the branching ratio of $J \pi (^{65}\text{Zn} ) = 5/2^- \rightarrow J \pi (^{65}\text{Cu}) = 5/2^- $ via electron capture (EC*). We measure the relative intensity of this branch to that proceeding directly to the ground state (EC$^0$) using a novel coincidence technique, finding $I_{\text{EC}^0}/I_{\text{EC*}} = 0.9684 \pm 0.0018$. Re-evaluating the decay scheme of $^{65}$Zn by adopting the commonly evaluated branching ratio of $I_{\beta^+}= 1.4271(7)\%$ we obtain $I_{\text{EC*}} = (50.08 \pm 0.06)\%$, and $I_\text{EC^0} = (48.50 \pm 0.06) \%$. The associated 1115 keV gamma intensity agrees with the previously reported NNDC value, and is now accessible with a factor of ~2 increase in precision. Our re-evaluation removes reliance on the deduction of this gamma intensity from numerous measurements, some of which disagree and depend directly on total activity determination. The KDK experimental technique provides a new avenue for verification or updates to the decay scheme of $^{65}$Zn, and is applicable to other isotopes.
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