Fritz Bosch, the ESR and the Bound-State Beta-Decay of 205Tl

This will be a talk in honor of Fritz Bosch to celebrate his 84th birthday. It is now nearly eight years that we lost him. But, I guess, he is still well known and very much liked at GSI. Fritz can be called the nuclear father of the Experimental Storage Ring (ESR) of GSI because right from the beginning he thought about the possibilities to use it to answer questions and solve problems in nuclear physics. His primary interest was the never before observed process of bound-state beta-decay. I will explain the first two successful experiments on 163Dy, which is stable as an atom, but decays to 163Ho when it is a bare nucleus, and 187Re, which decays about 109 times faster, when all electrons are removed. The latter result was essential to estimate the age of our Galaxy and thus of the universe from the ratio of 187Os/187Re in meteorites. In that context I will describe the ESR. The most recent success was the measurement of the half-life of bare 205Tl nuclei (T1/2=291+33-27 days) which again are stable as neutral atoms. This experiment was held up for a long time, because Thallium is poisonous and could not be used in an ion source. Therefore, the 205Tl had to be produced from a 206Pb primary beam. When a proton was lost in the target at the entrance of the FRS, the remaining 205Tl ions were separated from the 206Pb beam in the FRS and then injected into the ESR. This half-life, which could be predicted by theory only with very large uncertainty, turned out to be about five times longer than predicted and is of importance for two applications:

1) To estimate from the 205Pb/204Pb ratio in meteorites, how long the material from which the Solar System formed was not exposed to influx from nucleosynthetic events (s-process) (Guy Leckenby et al., Nature 635 (2024) 321).

2) There is a nearly 50 years old discussion to use the 205Pb (half-life of neutral atoms 17 Myr) content in Thallium bearing minerals as a long term Solar neutrino detector (LOREX) via the reaction 205Tl(ν,e-)205Pb. With our measured half-life a reliable prediction for the rate of neutrino captures can be given, making the LOREX experiment more difficult than earlier estimates (Ragandeep Singh Sidhu et al., Phys. Rev. Lett. 133 (2024) 232701).