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論文

Competition between allowed and first-forbidden $$beta$$ decay; The Case of $$^{208}$$Hg $$rightarrow$$ $$^{208}$$Tl

Carroll, R. J.*; Podoly$'a$k, Zs.*; Berry, T.*; Grawe, H.*; Alexander, T.*; Andreyev, A. N.; Ansari, S.*; Borge, M. J. G.*; Brunet, M.*; Creswell, J. R.*; et al.

Physical Review Letters, 125(19), p.192501_1 - 192501_6, 2020/11

 被引用回数:3 パーセンタイル:63.95(Physics, Multidisciplinary)

The $$beta$$ decay of $$^{208}$$Hg into the one-proton hole, one neutron-particle $$^{208}_{81}$$Tl$$_{127}$$ nucleus was investigated at CERN-ISOLDE. Shell-model calculations describe well the level scheme deduced, validating the proton-neutron interactions used, with implications for the whole of the $$N > 126$$, $$Z < 82$$ quadrant of neutron-rich nuclei. While both negative and positive parity states with spin 0 and 1 are expected within the $$Q_{beta}$$ window, only three negative parity states are populated directly in the $$beta$$ decay. The data provide a unique test of the competition between allowed Gamow-Teller and Fermi, and first-forbidden $$beta$$ decays, essential for the understanding of the nucleosynthesis of heavy nuclei in the rapid neutron capture process. Furthermore, the observation of the parity changing $$0^{+} rightarrow 0^{-} beta$$ decay where the daughter state is core excited is unique, and can provide information on mesonic corrections of effective operators.

論文

Investigation of the $$Delta$$$$n$$ = 0 selection rule in Gamow-Teller transitions; The $$beta$$-decay of $$^{207}$$Hg

Berry, T. A.*; Podoly$'a$k, Zs.*; Carroll, R. J.*; Lic$u{a}$, R.*; Grawe, H.*; Timofeyuk, N. K.*; Alexander, T.*; Andreyev, A. N.; Ansari, S.*; Borge, M. J. G.*; et al.

Physics Letters B, 793, p.271 - 275, 2019/06

 被引用回数:3 パーセンタイル:52.47(Astronomy & Astrophysics)

Gamow-Teller $$beta$$ decay is forbidden if the number of nodes in the radial wave functions of the initial and final states is different. This $$Delta$$$$n$$ = 0 requirement plays a major role in the $$beta$$ decay of heavy neutron-rich nuclei, affecting the nucleosynthesis through the increased half-lives of nuclei on the astrophysical $$r$$-process pathway below both $$Z$$ = 50 (for $$N >$$ 82) and $$Z$$ = 82 (for $$N >$$ 126). The level of forbiddenness of the $$Delta$$$$n$$ = 1 $$nu$$1$$g_{9/2} rightarrow pi$$0$$g_{7/2}$$ transition has been investigated from the $$beta^{-}$$ decay of the ground state of $$^{207}$$Hg into the single-proton-hole nucleus $$^{207}$$Tl in an experiment at the ISOLDE Decay Station. From statistical observational limits on possible $$gamma$$-ray transitions depopulating the $$pi$$0$$g^{-1}_{7/2}$$ state in $$^{207}$$Tl, an upper limit of 3.9$$times$$10$$^{-3}$$ % was obtained for the probability of this decay, corresponding to log$$ft >$$ 8.8 within a 95% confidence limit. This is the most stringent test of the $$Delta$$$$n$$ = 0 selection rule to date.

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