• Thu. Feb 29th, 2024

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

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

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(a) Example showing interactions within LiInSe2 Crystal detector. (b) Simulations (red) combined with the expected but incorrectly reconstructed distribution of events (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 so long-lived that half the atoms of indium take 100 trillion years to decay. These isotopes allow scientists to investigate the precise internal processes that control other long-lived isotopes. The new research is helping scientists improve the frameworks they use to calculate half-lives and other nuclear properties, such as the composition of protons/neutrons inside the nucleus.

Using background simulation/subtraction techniques pioneered in other ton-scale nuclear decay experiments, the scientists extracted the energy spectrum of electrons ejected from the decay of In-115 that occurred inside a LiInSe.2 Crystal. Meanwhile, the scientists also made the world’s most accurate measurement of the decay rate of In-115. This work expands scientific understanding of nuclear structure and paves the way for future experiments to investigate nuclear structure for different isotope sizes.

The physical processes that determine the decay rates of mid-size nuclei are difficult for scientists to investigate. This is due to the large number of intermediate nuclear energy states. This study demonstrates the feasibility of extracting pure electron (beta) energy spectra from various long-lived nuclei using low-temperature crystal detectors.

The research enables scientists to reduce uncertainties involving intermediate energy states that play a role in long-lived nuclei. This will allow better modeling of complex nuclear systems such as the double beta decay of tellurium-130. Reducing these uncertainties plays an important role in improving the performance of other ton-scale nuclear fission experiments sponsored by the Department of Energy.

A collaboration including the University of California-Berkeley, the Massachusetts Institute of Technology, the University of Jyväskylä in Finland, the Université Paris-Saclay, and RMD Inc. commissioned a new LiInSe.2 detector to explore the potential of high-quality, low-background bolometric detectors for use in nuclear decay model verification.

The researchers collected near-absolute zero data to detect and record the tiniest spikes in temperature caused by particle interactions from In-115 beta decay using highly sensitive thermometers. The study ruled out background events such as external gamma rays using a combination of particle simulations and close examination of individually recorded decay.

The result was a pure In-115 decay spectrum of ejected electrons. Scientists at the University of California, Berkeley compared this spectrum to a library of predicted spectra created at the University of Jyväskylä and found the predicted spectrum that most closely matched the collected data. This yielded the most accurate measurement to date of the decay rate of In-115. The measurement opens the door to a greater understanding of the physics governing the decay of long-lived isotopes such as tellurium-130.

The work has been published in the journal Physical Review Letters.

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

Journal Information:
Physical Review Letters


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