4 research outputs found
Precision measurement of Zn electron-capture decays with the KDK coincidence setup
Zn is a common calibration source, moreover used as a radioactive
tracer in medical and biological studies. In many cases, -spectroscopy
is a preferred method of Zn standardization, which relies directly on
the branching ratio of via electron capture (EC*). We measure the relative
intensity of this branch to that proceeding directly to the ground state
(EC) using a novel coincidence technique, finding
. Re-evaluating the decay
scheme of Zn by adopting the commonly evaluated branching ratio of
we obtain , 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 Zn, and is applicable to other isotopes.Comment: Uses similar methodology to the 40K measurement by the KDK
Collaboration (Stukel et al PRL 2023, arXiv:2211.10319; Hariasz et al PRC
2023, arXiv:2211.10343), as such there may be some similarity in figures and
tex
A novel experimental system for the KDK measurement of the K decay scheme relevant for rare event searches
Potassium-40 (K) is a long-lived, naturally occurring radioactive
isotope. The decay products are prominent backgrounds for many rare event
searches, including those involving NaI-based scintillators. K also
plays a role in geochronological dating techniques. The branching ratio of the
electron capture directly to the ground state of argon-40 has never been
measured, which can cause difficulty in interpreting certain results or can
lead to lack of precision depending on the field and analysis technique. The
KDK (Potassium (K) Decay (DK)) collaboration is measuring this decay. A
composite method has a silicon drift detector with an enriched, thermally
deposited K source inside the Modular Total Absorption Spectrometer.
This setup has been characterized in terms of energy calibration, gamma tagging
efficiency, live time and false negatives and positives. A complementary,
homogeneous, method is also discussed; it employs a KSrI:Eu
scintillator as source and detector.Comment: 20 pages, 24 figures, Submitted to NIM
Evidence for ground-state electron capture of K
Potassium-40 is a widespread 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
K, but a predicted electron-capture decay directly to the ground state
of argon-40 has never been observed, while theoretical predictions span an
order of magnitude. The KDK Collaboration reports on the first observation of
this rare decay, obtained using a novel combination of a low-threshold X-ray
detector surrounded by a tonne-scale, high-efficiency -ray tagger at
Oak Ridge National Laboratory. A blinded analysis reveals a distinctly nonzero
ratio of intensities of ground-state electron-captures () over
excited-state ones () of
(68% CL), with the null hypothesis rejected at 4 [Stukel et al.,
DOI:10.1103/PhysRevLett.131.052503]. This unambiguous signal yields a branching
ratio of
,
roughly half of the commonly used prediction. This first observation of a
third-forbidden unique electron capture improves understanding of low-energy
backgrounds in dark-matter searches and has implications for nuclear-structure
calculations. A shell-model based theoretical estimate for the
decay half-life of calcium-48 is increased by a factor of . Our
nonzero measurement shifts geochronological ages by up to a percent;
implications are illustrated for Earth and solar system chronologies.Comment: This is a companion submission to Stukel et al (KDK collaboration)
"Rare K decay with implications for fundamental physics and
geochronology" [arXiv:2211.10319; DOI: 10.1103/PhysRevLett.131.052503]. As
such, both texts share some figures and portions of text. This version
updates the text following its review and production proces