Long-sought measurement of exotic beta decay in thallium helps extract the timescale of the birth of the Sun

An international collaboration of scientists succeeded in the measurement of the bound-state beta decay of fully-ionised thallium (205Tl81+) ions at the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt. The experiment, conducted at the Experimental Storage Ring (ESR) of GSI/FAIR and analysed in partnership with TRIUMF, Vancouver, revealed that the half-life of bare 205Tl81+ days, twice as long as theoretically expected. This measurement has profound effects on the production of radioactive lead (205Pb) in asymptotic giant branch (AGB) stars, which were simulated by collaborators at Konkoly Observatory, Budapest, and can be used to help determine how long the Sun took to form in the early Solar System. The results have been published in the journal Nature.

Bound-state beta decay is an exotic decay mode that only occurs in highly charged ions and can turn a stable atom like 205Tl0+ into a radioactive ion when all electrons are removed (as in 205Tl81+). This unique decay mode has so far only been observed at the ESR, which is currently the only device capable of storing millions of fully ionised ions for several hours. 

“The measurement of 205Tl81+ had been proposed in the 1980s, but it has taken decades of accelerator development and the hard work of many colleagues to bring to fruition,” says Professor Yury Litvinov of GSI/FAIR, spokesperson of the experiment. “The 205Tl beam had to be created in GSI/FAIR’s Fragment Separator (FRS) in a nuclear reaction with many injections into the ESR required to reach a sufficient number of stored ions. The FRS team developed a groundbreaking new setting to achieve the required beam intensity for a successful experiment.”

The experiment was conducted in 2020 during the opening weeks of the COVID-19 lockdowns. “COVID definitely threw a spanner in the works, but the dedication of the local team saved the day,” says Guy Leckenby, doctoral student from TRIUMF and first author of the publication. “We perfected the analysis over three years, which was a worthwhile effort as the measured half-life of 291(+33)(-27) days is twice as long as what was estimated theoretically. This highlights the importance of making an experimental measurement.”

“By knowing the half-life, we can now accurately calculate the rates transforming 205Tl into 205Pb and back in different plasma environments inside stars. These values haven’t been revisited since the 1980s,” says Dr. Riccardo Mancino, who computed the rates as a post-doctoral researcher in theoretical physics at GSI/FAIR. “With modern computing and the new experimental result, we were able to provide significantly improved rates for the AGB models.”

The asymptotic giant branch (AGB) refers to stars of 0.5 to eight times the mass of our Sun at the end of their life cycle and is the site where some elements heavier than iron are produced in a process called slow neutron capture. Researchers from the Konkoly Observatory in Budapest (Hungary), the INAF Osservatorio d'Abruzzo (Italy), and the University of Hull (UK), implemented the new 205Tl/205Pb stellar decay rates in their state-of-the-art AGB astrophysical models. “Whilst the different models see slightly different results, the confidence in the new decay rates means we can be sure that AGB stars produced the 205Pb that once made its way into the gas cloud which formed our Sun,” explains Dr. Maria Lugaro, researcher at Konkoly Observatory. “Given the uncertainties in the amount of extinct 205Pb we currently see in meteorites, it seems that our new 205Pb result is giving a time interval for the collapse of the pre-solar gas cloud that is consistent with other radioactive species produced by the slow neutron capture process. In short, we are starting to assemble evidence for exactly how long it took for our Sun to form over 4.5 billion years ago.”

The measured bound-state beta decay half-life is essential to analyze the accumulation of 205Pb in the interstellar medium. However, more research accounting for the full history of the galaxy is needed to fully comprehend it. In addition to planned advanced simulations of galactic chemical evolution, a further measurement of the neutron capture rate on 205Pb by utilizing the surrogate reaction method in the ESR has been proposed. Numerous additional high-impact experiments are proposed forthe new heavy-ion storage rings planned at the future accelerator facility FAIR, which is currently under construction at GSI.

Yuri Litvinov's GSI group has been collaborating with the MPI for Nuclear Physics for many years, where he was a postdoc in the division of Klaus Blaum. In 2017, he was awarded with an adjunct professorship at the Ruprecht-Karls-University in Heidelberg.

The work is dedicated to deceased colleagues Fritz Bosch, Hans Geissel, Paul Kienle, and Fritz Nolden, who were supporting this research for many years.


Original publication:

High-temperature 205Tl decay clarifies 205Pb dating in early Solar System
Guy Leckenby, Ragandeep Singh Sidhu, Rui Jiu Chen, Riccardo Mancino, Balázs Szányi, Mei Bai, Umberto Battino, Klaus Blaum, Carsten Brandau, Sergio Cristallo, Timo Dickel, Iris Dillmann, Dmytro Dmytriiev, Thomas Faestermann, Oliver Forstner, Bernhard Franczak, Hans Geisse, Roman Gernhäuser, Jan Glorius, Chris Griffin, Alexandre Gumberidze, Emma Haettner, Pierre-Michel Hillenbrand, Amanda Karakas, Tejpreet Kaur, Wolfram Korten, Christophor Kozhuharov, Natalia Kuzminchuk, Karlheinz Langanke, Sergey Litvinov, Yuri A. Litvinov, Maria Lugaro, Gabriel Martínez Pinedo, Esther Menz, Bradley Meyer, Tino Morgenroth, Thomas Neff, Chiara Nociforo, Nikolaos Petridis, Marco Pignatari, Ulrich Popp, Sivaji Purushothaman, René Reifarth, Shahab Sanjari, Christoph Scheidenberger, Uwe Spillmann, Markus Steck, Thomas Stöhlker, Yoshiki K. Tanaka, Martino Trassinelli, Sergiy Trotsenko, László Varga, Diego Vescovi, Meng Wang, Helmut Weick, Andrés Yagüe Lopéz, Takayuki Yamaguchi, Yuhu Zhang and Jianwei Zhao
Nature (13.11.2024). DOI: 10.1038/s41586-024-08130-4


Weblinks:

Group 'ASTRUm - Astrophysics with Stored Highy Charged Radionuclides' (GSI)

Group 'Exotic Decay Spectroscopy' (TRIUMF)

Division 'Stored and Cooled Ions' at MPIK


Contact

apl. Prof. Dr. Yuri A. Litvinov
GSI Helmholtzzentrum für Schwerionenforschung
Phone: +49 6159 71-1758

Guy Leckenby
TRIUMF (Vancouver, BC, Kanada)
Phone: +420 26605 3665

Prof. Dr. Klaus Blaum
MPI für Kernphysik
Phone: +49 6221 516-850


Press & Public Outreach

Dr. Renate Hubele / PD Dr. Bernold Feuerstein
Phone: +49 6221 516-651 / +49 6221 516-281


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