Physicists are Potassium Decay (KDK) Collaboration. They directly observed for the first time a very rare but important decay pathway from potassium-40 to argon-40. Their results have the potential to improve current understanding of physical processes and increase the accuracy of geological dating.

Potassium-40 is a ubiquitous natural isotope whose radioactivity has been used to estimate geological ages over billions of years, to theories of nuclear structure, and to the search for subatomic rare events such as dark matter and neutrinoless double beta decay. influence.

The decay of this long-lived isotope must be precisely known for its use as a global clock and to explain its presence in low-background experiments.

Although potassium-40 has several known decay modes, the electron-capture decay predicted directly into the ground state of argon-40 has never been observed before.

“Some of the nuclei of certain elements radioactively decay into the nuclei of other elements. These decays can be helpful or annoying, depending on the situation,” the KDK physicists said. I am.

“This is especially true for potassium-40, an isotope that normally decays to calcium-40, but about 10% of the time it decays to argon-40.”

“This decay pathway involves a process called electron capture, which provides information about the nuclear structure.”

“Potassium-40 has a very long half-life, so it can even determine the age of geological objects on billion-year time scales.”

“Due to its long half-life, it is difficult to find another way for potassium-40 to break down.”

In a new study, researchers measured a rare decay branch of potassium-40 at Oak Ridge National Laboratory's Holyfield Radioactive Ion Beam Facility.

“Quantifying the decay rate of potassium-40 and its decay branches is difficult because it requires measuring the parent nucleus and a sufficient number of rare progeny nuclei,” the researchers said.

“We studied a subset of potassium-40 that decays to argon-40 by electron capture, which accounts for about 10% of all potassium-40 decays.”

“Although most potassium-40 electron-capture decays emit characteristic gamma rays that form the background of most experiments, a small subset of these decays occur without gamma ray emission.”

“This happens when potassium-40 captures an electron that goes directly to the ground state of argon-40.”

“We have directly measured this decay for the first time. This result indicates that other decay rates may also need to be reevaluated.”

“The rare decay branch we identified and measured provides unique experimental evidence for so-called forbidden beta decay, with implications for predictions of nuclear structure and for potassium-based geological and solar system age estimates. It removes years of uncertainty.”

“This discovery also improves our assessment of the background that exists in experiments that explore new physics beyond the Standard Model.”

The results are published in two papers (paper #1 and paper #2) in the diary physical review letter and diary Physical Review C.

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M. Stukel other. (KDK collaboration). 2024. 40,000 rare collapses with implications for fundamental physics and geochronology. Physics.pastor rhett 131 (5): 052503; doi: 10.1103/PhysRevLett.131.052503

L. Harias other. (KDK collaboration). 2024. Evidence of ground state electron capture at 40K. Physics. Rev.C 108 (1): 014327; doi: 10.1103/PhysRevC.108.014327