The Sun, a vital force for life on Earth, produces its immense energy through nuclear fusion. In this process, it also emits a constant flow of neutrinos—subatomic particles that act as indicators of its internal workings. While current neutrino detectors can reveal the Sun’s current activity, numerous important questions remain regarding its stability over millions of years—a span that encompasses human evolution and significant climatic shifts.
The LORandite EXperiment (LOREX) aims to address these questions by requiring precise knowledge of how solar neutrinos interact with thallium. A team of international scientists has successfully gathered this data at GSI/FAIR’s Experimental Storage Ring ESR in Darmstadt, producing a crucial measurement that will further our understanding of the Sun’s long-term stability. The findings have been published in the scientific journal Physical Review Letters.
LOREX is unique in its pursuit as the only ongoing geochemical solar neutrino project. Since its proposal in the 1980s, its goal has been to measure the solar neutrino flux averaged over an impressive four million years, which correlates with the geological age of lorandite ore.
Neutrinos generated in the Sun interact with thallium (Tl) atoms found in lorandite (TlAsS2), transforming them into lead (Pb) atoms. The isotope 205Pb is particularly noteworthy due to its extended half-life of 17 million years, rendering it fundamentally stable over the four million year timeline of the lorandite ore. Since measuring the neutrino cross-section on 205Tl directly isn’t currently feasible, researchers at GSI/FAIR in Darmstadt devised a clever approach to ascertain the necessary nuclear physics quantity for calculating the neutrino cross section. This required quantity, the nuclear matrix element, also governs the bound-state beta decay rate of fully ionized 205Tl81+ to 205Pb81+.
The experimental determination of the half-life for the bound-state beta decay of fully ionized 205Tl81+ ions was made possible solely due to the remarkable capabilities of the Experimental Storage Ring (ESR) at GSI/FAIR. Currently, the ESR is the exclusive facility where such measurements can be conducted. The 205Tl81+ ions were generated through nuclear reactions in GSI/FAIR’s Fragment Separator (FRS) and adequately stored for long enough to observe and measure its decay in the storage ring. Professor Yuri A. Litvinov, a spokesperson for the project and lead researcher for the European Research Council (ERC) Consolidator Grant ASTRUm, remarked, “Decades of consistent improvements in accelerator technology have enabled us to produce an intense and pure 205Tl81+ ion beam and measure its decay with high precision.”
“The half-life of 205Tl81+ beta decay was found to be 291 (+33/-27) days, a crucial measurement that facilitates the calculation of the solar neutrino capture cross-section,” shared Dr. Rui-Jiu Chen, a postdoctoral research associate on the team. As the LOREX project determines the concentration of 205Pb atoms in the lorandite minerals, it will pave the way for insights into the Sun’s evolutionary journey and its ties to the Earth’s climate across epochs.
“This groundbreaking experiment underscores the role of nuclear astrophysics in tackling fundamental inquiries about the universe,” noted Professor Gabriel MartÃnez-Pinedo and Dr. Thomas Neff, who led the theoretical efforts to convert the measurement into the neutrino cross-section.
Dr. Ragandeep Singh Sidhu, the lead author of the research paper, underscored the broader implications of the study: “This experimentation illustrates how a single, albeit challenging, measurement can be crucial in resolving significant scientific inquiries concerning the evolution of our Sun.”
The publication honors the memory of late colleagues Fritz Bosch, Hans Geissel, Paul Kienle, and Fritz Nolden, whose contributions were vital to the success of this project.
