Measurement of the 2+--0+ ground-state transition in the ß decay of 20F
12 pags., 16 figs., 4 tabs. ; We report the first detection of the second-forbidden, nonunique, 2+ → 0+, ground-state transition in the β decay of 20F. A low-energy, mass-separated 20F+ beam produced at the IGISOL facility in Jyväskylä, Finland, was implanted in a thin carbon foil and the β spectrum measured using a magnetic transporter and a plasticscintillator detector. The β-decay branching ratio inferred from the measurement is bβ = [0.41 ± 0.08(stat) ± 0.07(sys)] × 10−5 corresponding to log f t = 10.89(11), making this one of the strongest second-forbidden, nonunique β transitions ever measured. The experimental result is supported by shell-model calculations and has significant implications for the final evolution of stars that develop degenerate oxygen-neon cores. Using the new experimental data, we argue that the astrophysical electron-capture rate on 20Ne is now known to within better than 25% at the relevant temperatures and densities ; This work has been supported by the Academy of Finland under the Finnish Centre of Excellence Programme (Nuclear and Accelerator Based Physics Research at JYFL 2012-2017) and Academy of Finland Grants No. 275389, No. 284516, No. 295207, and No. 312544. D.F.S. and G.M.-P. acknowledge the support of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)-Projektnummer 279384907-SFB 1245 "Nuclei: From Fundamental Interactions to Structure and Stars"; and the ChETEC COST action (CA16117), funded by COST (European Cooperation in Science and Technology). This project has been partly supported by the Spanish Ministry MINECO through the grant FPA2015-64969-P and has received funding from the European Union's Horizon 2020 research and innovation programme under Grant Agreement No. 654002 (ENSAR2). O.S.K. acknowledges support from the Villum Foundation through Project No. 10117. P.C.S. acknowledges the support from the Faculty Initiation Grant (FIG) provided by IIT Roorkee. A.K. and M.H. acknowledge the support from the European Union's Horizon 2020 research and innovation program under Grant Agreement No. 771036 (ERC CoG MAIDEN). B.A.B. acknowledges the support from NSF Grant PHY-1811855.