Eyes on the Sun thallium decay study sheds light on solar history

Eyes on the Sun thallium decay study sheds light on solar history
by Robert Schreiber
Berlin, Germany (SPX) Dec 13, 2024

The Sun powers life on Earth, generating immense energy through nuclear fusion and continuously releasing neutrinos - particles that provide insight into its inner workings. While modern neutrino detectors capture the Sun's present behavior, questions about its long-term stability over millions of years remain unanswered. Addressing this challenge is the focus of the LORandite EXperiment (LOREX), which requires precise measurements of the solar neutrino cross-section on thallium.

A significant breakthrough in this endeavor was achieved by an international team of scientists at GSI/FAIR's Experimental Storage Ring (ESR) in Darmstadt, Germany. Their findings, recently published in *Physical Review Letters*, deliver critical data for understanding the Sun's long-term behavior.

The LOREX project, first proposed in the 1980s, is the only long-term geochemical solar neutrino experiment still underway. It aims to measure solar neutrino flux averaged over four million years, the geological age of lorandite ore. When neutrinos interact with thallium atoms in lorandite (TlAsS2), they convert them into lead atoms, specifically the isotope 205Pb. With a half-life of 17 million years, this isotope's stability aligns well with LOREX's ambitious timescales.

Directly measuring the neutrino cross-section on 205Tl remains infeasible. To overcome this, researchers at GSI/FAIR used an innovative approach, leveraging the connection between this cross-section and the bound-state beta decay of fully ionized 205Tl81+ ions to 205Pb81+. The ESR facility's unique capabilities enabled the successful measurement of this decay.

"Decades of advancements in accelerator technology allowed us to generate an intense and pure 205Tl81+ ion beam and measure its decay with high precision," said Professor Yuri A. Litvinov, the experiment's spokesperson and principal investigator for the European Research Council's ASTRUm grant.

The team determined the half-life of 205Tl81+ beta decay to be 291 (+33/-27) days, a key result for calculating the solar neutrino capture cross-section. With this data, LOREX can evaluate the concentration of 205Pb in lorandite minerals to provide insights into the Sun's history and its impact on Earth's climate over millennia.

"This experiment demonstrates the profound role of nuclear astrophysics in addressing fundamental questions about the universe," commented Professor Gabriel Martinez-Pinedo and Dr. Thomas Neff, who led the theoretical work on converting the experimental data into neutrino cross-section values.

Dr. Ragandeep Singh Sidhu, lead author of the publication, highlighted its broader implications: "This challenging measurement exemplifies how a single scientific achievement can address pivotal questions regarding the Sun's evolution."

The findings mark a milestone in the study of solar history, showcasing the synergy of cutting-edge experimental physics and theoretical modeling.

Research Report:Bound-State Beta Decay of 205Tl81+ Ions and the LOREX Project