Nuclei in the Cosmos XII - Satellite Workshop

β decays of the isotones with N = 126 are studied by shell-model calculations taking into account both the Gamow-Teller (GT) and first-forbidden (FF) transitions [1]. Shell-model interaction of Ref. [2] is adopted and a quenching of g_A^{eff}/g_A =0.7 is used for both the GT and FF transitions except for 0^{-} case. The FF transitions [3] are found to be important to reduce the beta-decay half-lives, by nearly twice to several times, from those by the GT contributions only. The half-lives obtained here are short compared with the standard data of FRDM [4] except for Z = 71 usually employed in nucleosynthesis network calculations. They increase monotonically as Z increases showing no odd-even staggering found in FRDM's. They are, on the other hand, longer than those of CQRPA calculations [5]. Possible implications of the short half-lives of the waiting point nuclei on the r-process nucleosynthesis during the supernova explosions are discussed. A slight shift of the third peak of the element abundances in the r process toward a higher mass region is found. The dependence of the \beta-decay half-lives and the r-process nucleosynthesis on the magnitudes of the quenching of g_A and g_V in FF transitions is studied. Large quenchings are found to be necessary for FF transitions in $^{206}$Hg [6]. FF transitions in nuclei at and near the N=126 isotones such as 204Pt, 203Pt, 202Ir and 201Ir are also investigated. Calculated half-lives of these nuclei are compared with recent experimental data [7] and the quenching of g_A and g_V are discussed. [1] T. Suzuki, T. Yoshida, T. Kajino and T．Otsuka, Phys. Rev. C 85, 015802 (2012). [2] S. J. Steer et al., Phys. Rev. C78, 061302 (2008); L. Rydstrom, J. Blomqvist, R. J. Liotta, and C. Pomar, Nucl. Phys. A 512, 217 (1990). [3] E. K. Warburton, J. A. Becker, B. A. Brown, and D. J. Millener, Ann. Phys. 187, 471 (1988); H. Behrens and W. B¨uhring, Nucl. Phys. A 162, 111 (1971); H. Schopper, Weak Interactions and Nuclear Beta Decays (North-Holland, Amsterdam, 1966); I. S. Towner and J. C. Hardy, Nucl. Phys. A 179, 489 (1972). [4] P.Moller, J. R. Nix, and K.-L. Kratz, At. Data Nucl. Data Tables 66, 131 (1997); P.Moller, B. Pfeiffer, and K.-L. Kratz, Phys. Rev. C 67, 055802 (2003). [5] I. N. Borzov, Phys. Rev. C 67, 025802 (2003). [6] E. K. Warburton, Phys. Rev. C 44, 233 (1991); ibid. 42, 2479 81990). [7] J. Benlliure et al., ARIS 2011.