The KDK (potassium decay) experiment

Stefano, P. C. F. Di; Brewer, N. T.; Fijałkowska, A.; Gai, Zheng; Goetz, K. C.; Grzywacz, R.; Hamm, Daniel; Lechner, P.; Liu, Y.; Lukosi, Eric; Mancuso, M.; Melcher, Charles L.; Ninković, J.; Petricca, F.; Rasco, A. C.; Rouleau, Christopher M.; Rykaczewski, K. P.; Squillari, P.; Stand, Luis; Stracener, D. W.; Stukel, Matthew; WoliĔska-Cichocka, M.; Yavin, Itay

doi:10.1088/1742-6596/1342/1/012062

Cited by 5 publications

(8 citation statements)

References 13 publications

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“…where x is the shell, n x is the relative occupation number, C x contains the dependence of electron capture rates on nu-clear structure giving the forbiddenness classification, similar to the shape factor in β decay (Emery, 1975), f x is the integrated fermi function in β decay, f β + is the integrated positron spectrum, and C(W ) is the theoretical shape factor for allowed or forbidden transitions. A review of shape factors for 40 K transitions is provided by Cresswell et al (2018Cresswell et al ( , 2019.…”

Section: Theory and Calculation Of Ec Ground /β +mentioning

confidence: 99%

“…Unlike 40 K, the dominant decay of 22 Na is the β + decay mode. This is due to the greater difference in energy between the initial and final states, as positron decay will have a greater possibility of occurring in decays with a greater mass differences between initial and final states (Emery, 1975). 22 Na is not a perfect analogue; however, it is probably the best choice that 2010and Leutz et al (1965).…”

Section: Comparison With 22 Namentioning

confidence: 99%

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Production of 40Ar by an overlooked mode of 40K decay with implications for K-Ar geochronology

et al. 2020

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Abstract. The decay of 40K to the stable isotopes 40Ca and 40Ar is used as a measure of time for both the K-Ca and K-Ar geochronometers, the latter of which is most generally utilized by the variant 40Ar∕39Ar system. The increasing precision of geochronology has forced practitioners to deal with the systematic uncertainties rooted in all radioisotope dating methods. A major component of these systematic uncertainties for the K-Ar and 40Ar∕39Ar techniques is imprecisely determined decay constants and an incomplete knowledge of the decay scheme of 40K. Recent geochronology studies question whether 40K can decay to 40Ar via an electron capture directly to ground state (ECground), citing the lack of experimental verification as reasoning for its omission. In this study, we (1) provide a theoretical argument in favor of the presence of this decay mode and (2) evaluate the magnitude of this decay mode by calculating the electron capture to positron ratio (ECground/β+) and comparing calculated ratios to previously published calculations, which yield ECground/β+ between 150–212. We provide support for this calculation through comparison of the experimentally verified ECground/β+ ratio of 22Na with our calculation using the theory of β decay. When combined with measured values of β+ and β− decay rates, the best estimate for the calculated ECground/β+ for 40K yields a partial decay constant for 40K direct to ground-state 40Ar of 11.6±1.5×10-13 a−1 (2σ). We calculate a partial decay constant of 40K to 40Ar of 0.592±0.014×10-10 a−1 and a total decay constant of 5.475±0.107×10-10 a−1 (2σ), and we conclude that although omission of this decay mode can be significant for K-Ar dating, it is minor for 40Ar∕39Ar geochronology and is therefore unlikely to have significantly biased published measurements.

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Section: Theory and Calculation Of Ec Ground /β +mentioning

confidence: 99%

Section: Comparison With 22 Namentioning

confidence: 99%

Production of 40Ar by an overlooked mode of 40K decay with implications for K-Ar geochronology

et al. 2020

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“…In the case of 40 K, verification of the EC ground decay can be achieved by measuring the characteristic x-rays (Di Stefano et al, 2017). The orbital electron with the highest probability of capture is from the K-shell; if this electron is captured, it results in https://doi.org/10.5194/gchron-2020-9 Preprint.…”

Section: Experimental Verification Of Ec Ground Decay Modementioning

confidence: 99%

“…However, electron capture to both the ground and excited state of 40 Ar ( 40 Ar 2+) result in the same electron configuration and x-ray emissions. Di Stefano et al (2017) suggested tagging x-rays with the de-excitation γ associated with electron capture to 40 Ar 2+ , which has a lifetime on the order of ~ 10 -12 s (Di Stefano et al, 2017). X-rays tagged by the 1.46 MeV γ must correspond to electron capture to the excited 40 Ar 2+ state, with those x-rays not tagged correspond to the the electron capture to ground state decay.…”

Section: Experimental Verification Of Ec Ground Decay Modementioning

confidence: 99%

“…Ongoing attempts are being made to verify this decay mode by careful detection of the characteristic x-rays by the KDK experiment (Di Stefano et al, 2017;Stukel, 2018). Experimental verification has implications for (1) rare event physics, as it 280 is a vital component in constraining the irreducible background and verifying results in the DArk MAtter (DAMA) experiment (Pradler et al, 2013), (2) the theory of -decay (Fermi, 1934) as it is the only 3 rd order unique forbidden electron capture decay known (Audi et al, 2003), and (3) K-Ar and 40 Ar/ 39 Ar geochronology, for which it is currently overlooked due to lack of experiment evidence.…”

Section: Experimental Verification Of Ec Ground Decay Modementioning

confidence: 99%

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Percent-level production of 40Ar by an overlooked mode of 40K decay

Carter¹,

Ickert²,

Mark³

et al. 2020

Preprint

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Abstract. The decay of 40K to the stable isotopes 40Ca and 40Ar is used as a measure of time for both the K-Ca and K-Ar geochronometers, the latter of which is most generally utilized by the variant 40Ar/39Ar system. The increasing precision of geochronology has forced practitioners to deal with the systematic uncertainties rooted in all radioisotope dating methods. A major component of these systematic uncertainties for the K-Ar and 40Ar/39Ar techniques is imprecisely determined decay constants and an incomplete knowledge of the decay scheme of 40K. Recent studies question whether 40K can decay to 40Ar via an electron capture directly to ground state (ECground), citing the lack of experimental verification as reasoning for its omission. In this study, we (1) provide a theoretical argument in favour of the presence of this decay mode, and (2) evaluate the magnitude of this decay mode by calculating the electron capture to positron ratio (ECground&#8201;/&#8201;&#946;+) and after combining it with other estimates, provide a best estimate of 175&#8201;&#177;&#8201;65 (2&#963;). We provide support for this calculation through comparison of the experimentally verified ECground&#8201;/&#8201;&#946;+ ratio of 22Na with our calculation using the theory of &#946; decay.When combined with measured values of &#946;+ and &#946;- decay rates, this yields a partial decay constant for 40K direct to ground state 40Ar of 9.6&#8201;&#177;&#8201;3.8&#8201;&#215;&#8201;10&#8722;13&#8201;a&#8722;1 (2&#963;). We calculate a partial decay constant of 40K to 40Ar of 0.590&#8201;&#177;&#8201;0.014&#8201;&#215;&#8201;10&#8722;10&#8201;a&#8722;1, total decay constant of 5.473&#8201;&#177;&#8201;0.107&#8201;&#215;&#8201;10&#8722;10&#8201;a&#8722;1 (2&#963;), and conclude that although omission of this decay mode can be significant for K-Ar dating, it is minor for 40Ar/39Ar geochronology and is therefore unlikely to have significantly biased published measurements.

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Evidence for ground-state electron capture of K40

Hariasz,

Stukel,

Di Stefano

et al. 2023

Phys. Rev. C

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Potassium-40 is a widespread, naturally occurring isotope whose radioactivity impacts estimated geological ages spanning billions of years, nuclear structure theory, and subatomic rare-event searches-including those for dark matter and neutrinoless double-beta decay. The decays of this long-lived isotope must be precisely known for its use as a geochronometer, and to account for its presence in low-background experiments. There are several known decay modes for potassium-40, but a predicted electron-capture decay directly to the ground state of argon-40 has never been observed. The existence of this decay mode impacts several fields, while theoretical predictions span an order of magnitude. Here we report on the first, successful observation of this rare decay mode, obtained by the KDK (potassium decay) Collaboration using a novel combination of a low-threshold x-ray detector surrounded by a tonne-scale, high-efficiency γ -ray tagger at Oak Ridge National Laboratory. A blinded analysis reveals a distinctly nonzero ratio of intensities of ground-state electron-captures (I EC 0 ) over excitedstate ones (I EC* ) of I EC 0 /I EC* = 0.0095 stat ± 0.0022 sys ± 0.0010 (68% CL), with the null hypothesis rejected at 4σ [Stukel et al., Phys. Rev. Lett. 131, 052503 (2023)]. In terms of branching ratio, this unambiguous signal yieldsroughly half of the commonly used prediction. This first observation of a third-forbidden unique electron capture improves our understanding of low-energy backgrounds in dark-matter searches and has implications for nuclear-structure calculations. For example, a shell-model based theoretical estimate for the neutrinoless double-beta decay half-life of calcium-48 is increased by a factor of 7 +3 −2 . Our nonzero measurement shifts geochronological ages by up to a percent; implications are illustrated for Earth and solar system chronologies.

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The KDK (potassium decay) experiment

Cited by 5 publications

References 13 publications

Production of <sup>40</sup>Ar by an overlooked mode of <sup>40</sup>K decay with implications for K-Ar geochronology

Production of <sup>40</sup>Ar by an overlooked mode of <sup>40</sup>K decay with implications for K-Ar geochronology

Percent-level production of <sup>40</sup>Ar by an overlooked mode of <sup>40</sup>K decay

Evidence for ground-state electron capture of K40

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The KDK (potassium decay) experiment

Cited by 5 publications

References 13 publications

Production of &lt;sup&gt;40&lt;/sup&gt;Ar by an overlooked mode of &lt;sup&gt;40&lt;/sup&gt;K decay with implications for K-Ar geochronology

Production of &lt;sup&gt;40&lt;/sup&gt;Ar by an overlooked mode of &lt;sup&gt;40&lt;/sup&gt;K decay with implications for K-Ar geochronology

Percent-level production of &lt;sup&gt;40&lt;/sup&gt;Ar by an overlooked mode of &lt;sup&gt;40&lt;/sup&gt;K decay

Evidence for ground-state electron capture of K40

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Production of <sup>40</sup>Ar by an overlooked mode of <sup>40</sup>K decay with implications for K-Ar geochronology

Production of <sup>40</sup>Ar by an overlooked mode of <sup>40</sup>K decay with implications for K-Ar geochronology

Percent-level production of <sup>40</sup>Ar by an overlooked mode of <sup>40</sup>K decay