Abstract
The first ever search for \(\alpha \) decays to the first excited state in Yb was performed for six isotopes of hafnium (174, 176, 177, 178, 179, 180) using a high purity Hf sample of natural isotopic abundance with a mass of 179.8 g. For \(^{179}\)Hf, also \(\alpha \) decay to the ground state of \(^{175}\)Yb was searched for thanks to the \(\beta \)-instability of the daughter nuclide \(^{175}\)Yb. The measurements were conducted using an ultra-low-background HPGe-detector system located 225 m underground. After 75 days of data taking no decays were detected but lower bounds for the half-lives of the decays were derived on the level of \(\lim T_{1/2}\sim 10^{15}{-}10^{18}\) a. The decay with the shortest half-life based on theoretical calculation is the decay of \(^{174}\)Hf to the first \(2^+\) 84.3 keV excited level of \(^{170}\)Yb. The experimental lower bound was found to be \(T_{1/2}\ge 3.3\times 10^{15}\) a.
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Data Availability Statement
This manuscript has no associated data or the data will not be deposited. [Authors’ comment: The data can be supplied by the authors on demand.]
Notes
In the spectrum of the detector Ge10 there is a structure near the energy of interest with an area \(20.2 \pm 10.2\) counts, which is no evidence of the effect searched for (see text below and Fig. 5).
One can see in Table 5 that the strongest half-life limit was obtained with the detector Ge7 in set-up I. However, the large \(\lim T_{1/2}\) appears due to a negative peak area, which results in a small \(\lim S\) value. We prefer to use the estimation obtained from the higher statistics acquired with the detector Ge7 in set-ups I and II.
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Acknowledgements
This project received support from the EC-JRC open access project EUFRAT under Horizon2020. The group from the Institute for Nuclear Research (Kyiv, Ukraine) was supported in part by the program of the National Academy of Sciences of Ukraine “Fundamental research on high-energy physics and nuclear physics (international cooperation)”. D.V.K. and O.G.P. were supported in part by the project “Investigations of rare nuclear processes” of the program of the National Academy of Sciences of Ukraine “Laboratory of young scientists” (Grant No. 0118U002328).
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Communicated by S. Bhattacharya
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Danevich, F.A., Hult, M., Kasperovych, D.V. et al. First search for \(\alpha \) decays of naturally occurring Hf nuclides with emission of \(\gamma \) quanta. Eur. Phys. J. A 56, 5 (2020). https://doi.org/10.1140/epja/s10050-019-00005-x
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DOI: https://doi.org/10.1140/epja/s10050-019-00005-x