Speaker
Description
Lead-205 looks like a promising cosmochronometer for the early Solar System due to its unique position among astrophysically short-lived radionuclides as an s-only isotope probing the termination of the s process [1]. Unfortunately, the 2.3 keV first excited state in $^{205}$Pb reduces the half-life in stellar environments by around 6 orders of magnitude, which could severely inhibit $^{205}$Pb production. However, Yokoi et. al. [2] pointed out that the bound-state $\beta$ decay of $^{205}$Tl could counter-balance this decay by producing $^{205}$Pb. To clarify the complex production of $^{205}$Pb, we measured the bound-state $\beta$ decay of $^{205}$Tl$^{81+}$ at the Experimental Storage Ring in GSI, Darmstadt. From the measured half-life, we calculated new weak decay rates for a wide range of astrophysical conditions. AGB stellar nucleosynthesis models based on these new rates saw approximately a factor 2 increase in $^{205}$Pb production (when legacy rates were controlled). With new production ratios, we predicted an updated steady-state interstellar medium (ISM) $^{205}$Pb/$^{204}$Pb ratio. By comparing the ISM ratio to the ratio measured in the earliest meteorites, we derived, for the first time, a positive time interval for the isolation period of the solar material from enrichment.
[1] Lugaro (2018) PPNP 102:1–47.
[2] Yokoi (1985) A&A 145:339–346.
