近日，加拿大粒子与核物理国家实验室的Guy Leckenby与德国马克思普朗克核物理研究所的Rui Jiu Chen等人合作并取得一项新进展。经过不懈努力，他们证实高温²⁰⁵Tl衰变揭示早期太阳系中²⁰⁵Pb的定年信息。相关研究成果已于2024年11月13日在国际权威学术期刊《自然》上发表。

据悉，具有数百万年寿命的放射性原子核能够揭示太阳的形成历史，以及在其诞生时间和地点发生的活跃核合成过程。在最古老的陨石中发现的衰变特征中，²⁰⁵Pb是一个强有力的例证，因为它完全是通过慢中子捕获（s过程）产生的，其中大部分是在渐近巨星支（AGB）恒星中合成的。然而，由于²⁰⁵Pb和²⁰⁵Tl在恒星温度下的弱衰变速率非常不确定，因此迄今为止无法对²⁰⁵Pb的丰度进行准确预测。

为了限制这些衰变速率，该研究团队首次测量了完全电离的205Tl⁸¹⁺的束缚态β衰变，这是一种仅在高电荷离子中发生的特殊衰变模式。测得的半衰期比以前的理论估计长了4.7倍，并且10%的实验不确定性已经消除了主要的核物理限制。利用新的、有实验支持的衰变速率，研究人员使用渐近巨星支（AGB）恒星模型来计算²⁰⁵Pb的产额。

将这些产量与基本的银河化学演化（GCE）模型相结合，并与陨石中的²⁰⁵Pb/²⁰⁴Pb比值进行比较，研究人员确定了太阳物质在其母分子云中的隔离时间。研究人员得出的隔离时间为正值，与在早期太阳系中发现的其他s过程短寿命放射性核素相一致。这项研究结果再次证实了太阳诞生地为一个长寿命的巨大分子云，并支持将²⁰⁵Pb-²⁰⁵Tl衰变系统作为早期太阳系的计时器。

附：英文原文

Title: High-temperature ²⁰⁵Tl decay clarifies ²⁰⁵Pb dating in early Solar System

Author: Leckenby, Guy, Sidhu, Ragandeep Singh, Chen, Rui Jiu, Mancino, Riccardo, Sznyi, Balzs, Bai, Mei, Battino, Umberto, Blaum, Klaus, Brandau, Carsten, Cristallo, Sergio, Dickel, Timo, Dillmann, Iris, Dmytriiev, Dmytro, Faestermann, Thomas, Forstner, Oliver, Franczak, Bernhard, Geissel, Hans, Gernhuser, Roman, Glorius, Jan, Griffin, Chris, Gumberidze, Alexandre, Haettner, Emma, Hillenbrand, Pierre-Michel, Karakas, Amanda, Kaur, Tejpreet, Korten, Wolfram, Kozhuharov, Christophor, Kuzminchuk, Natalia, Langanke, Karlheinz, Litvinov, Sergey, Litvinov, Yuri A., Lugaro, Maria, Martnez-Pinedo, Gabriel, Menz, Esther, Meyer, Bradley, Morgenroth, Tino, Neff, Thomas, Nociforo, Chiara, Petridis, Nikolaos, Pignatari, Marco, Popp, Ulrich, Purushothaman, Sivaji, Reifarth, Ren, Sanjari, Shahab, Scheidenberger, Christoph, Spillmann, Uwe, Steck, Markus, Sthlker, Thomas, Tanaka, Yoshiki K., Trassinelli, Martino, Trotsenko, Sergiy, Varga, Lszl, Vescovi, Diego, Wang, Meng, Weick, Helmut, Yage Lopz, Andrs, Yamaguchi, Takayuki

Issue&Volume: 2024-11-13

Abstract: Radioactive nuclei with lifetimes on the order of millions of years can reveal the formation history of the Sun and active nucleosynthesis occurring at the time and place of its birth. Among such nuclei whose decay signatures are found in the oldest meteorites, ²⁰⁵Pb is a powerful example, as it is produced exclusively by slow neutron captures (the s process), with most being synthesized in asymptotic giant branch (AGB) stars. However, making accurate abundance predictions for ²⁰⁵Pb has so far been impossible because the weak decay rates of ²⁰⁵Pb and ²⁰⁵Tl are very uncertain at stellar temperatures. To constrain these decay rates, we measured for the first time the bound-state β decay of fully ionized ²⁰⁵Tl⁸¹⁺, an exotic decay mode that only occurs in highly charged ions. The measured half-life is 4.7times longer than the previous theoretical estimate and our 10% experimental uncertainty has eliminated the main nuclear-physics limitation. With new, experimentally backed decay rates, we used AGB stellar models to calculate ²⁰⁵Pb yields. Propagating those yields with basic galactic chemical evolution (GCE) and comparing with the ²⁰⁵Pb/²⁰⁴Pb ratio from meteorites, we determined the isolation time of solar material inside its parent molecular cloud. We find positive isolation times that are consistent with the other s-process short-lived radioactive nuclei found in the early Solar System. Our results reaffirm the site of the Sun’s birth as a long-lived, giant molecular cloud and support the use of the ²⁰⁵Pb–²⁰⁵Tl decay system as a chronometer in the early Solar System.

DOI: 10.1038/s41586-024-08130-4

Source: https://www.nature.com/articles/s41586-024-08130-4