Precision Nuclear Physics in the Indium-115 Beta Decay Spectrum Using Cryogenic Detectors

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(a) Example of a simulation showing the interactions within the LiInSe2 crystal detector. (b) The simulations (red) are combined with the predicted but incorrectly reconstructed event distribution (dashed blue) to extract a single In-115 spectrum (solid) from the data (black). Credit: Daniel Mayer/Alexander Leder

Some isotopes such as Indium-115 (In-115) are extremely long-lived, taking over 100 trillion years for half of the indium atoms to decompose. These isotopes allow scientists to probe the precise internal processes that govern other extremely long-lived isotopes. New research is helping scientists improve the structures they use to calculate half-lives and other nuclear properties, such as the structure of protons/neutrons within the nucleus.

Using background subtraction/simulation techniques pioneered in other ton-scale nuclear decay experiments, the scientists extracted the energy spectrum of the outgoing electrons from In-115 decays that occurred within a LiInSe2 crystal. At the same time, the scientists also performed the world’s most precise measurement of the decay rate of In-115. This work expands scientific understanding of nuclear structure and paves the way for future experiments to probe nuclear structure for a variety of isotope sizes.

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The physical processes that drive the decay rate of medium-sized nuclei are difficult for scientists to probe. This is due to the large number of intermediate nuclear energy states. This study shows the feasibility of extracting clean electron (beta) energy spectra from various long-lived nuclei using low-temperature crystal detectors.

The research allows scientists to reduce the uncertainties related to the intermediate energy states that play a role in long-lived nuclei. This would then allow for better modeling of complex nuclear systems, such as the double beta decay of tellurium-130. Reducing these uncertainties plays a key role in improving the performance of other Department of Energy-sponsored ton-scale nuclear decay experiments.

A collaboration between the University of California-Berkeley, Massachusetts Institute of Technology, Jyvasklya University in Finland, Paris-Saclay University and RMD Inc. has commissioned a new LiInSe2 detector to explore the possibility of high-quality, low-background bolometric detectors for use in nuclear decay model verification.

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The researchers collected data at temperatures close to absolute zero to detect and record the smallest temperature peaks due to particle interactions, such as those of In-115 beta decays, using highly sensitive thermometers. The study rejected background events such as external gamma rays using a combination of particle simulations and close examination of the individual decays recorded.

The result was a clean In-115 decay spectrum of the emitted electrons. Scientists at the University of California at Berkeley compared this spectrum to a library of predicted spectra generated at the University of Jyvaskyla and found the predicted spectrum most closely matched the collected data. This extracted the most precise measurement to date of the decay rate of In-115. This measurement opens the door to a better understanding of the physics governing the decays of extremely long-lived isotopes, such as tellurium-130.

The work is published in the journal Physical Review Letters.

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More information:
AF Leder et al, Determination of gA/gV with high resolution spectral measurements using a LiInSe2 bolometer, Physical Review Letters (2022). DOI: 10.1103/PhysRevLett.129.232502

About the magazine:
Physical Review Letters

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#Precision #Nuclear #Physics #Indium115 #Beta #Decay #Spectrum #Cryogenic #Detectors

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