Change in structure between the $I = 1/2$ states in $^{181}$Tl and $^{177,179}$Au

J.G. Cubiss , A.E. Barzakh , A.N. Andreyev , M. Al Monthery , N. Althubiti , B. Andel , S. Antalic , D. Atanasov , K. Blaum , T.E. Cocolios , T. Day Goodacre , R.P. de Groote , A. de Roubin , G.J. Farooq-Smith , D.V. Fedorov , V.N. Fedosseev , R. Ferrer , D.A. Fink , L.P. Gaffney , L. Ghys , A. Gredley , R.D. Harding , F. Herfurth , M. Huyse , N. Imai , D.T. Joss , U. Köster (1) , S. Kreim , V. Liberati , D. Lunney (2) , K.M. Lynch , V. Manea (2) , B.A. Marsh , Y. Martinez Palenzuela , P.L. Molkanov , P. Mosat , D. Neidherr , G.G. O'Neill , R.D. Page , T.J. Procter , E. Rapisarda , M. Rosenbusch , S. Rothe , K. Sandhu , L. Schweikhard , M.D. Seliverstov , S. Sels , P. Spagnoletti , V.L. Truesdale , C. van Beveren , P. van Duppen , M. Veinhard , M. Venhart , M. Veselský , F. Wearing , A. Welker , F. Wienholtz , R.N. Wolf , S.G. Zemlyanoy , K. Zuber

1 ILL - Institut Laue-Langevin
2 CSNSM - Centre de Sciences Nucléaires et de Sciences de la Matière

The first accurate measurements of the $\alpha$-decay branching ratio and half-life of the $I^{\pi}=1/2^+$ ground state in $^{181}$Tl have been made, along with the first determination of the magnetic moments and $I=1/2$ spin assignments of the ground states in $^{177,179}$Au. The results are discussed within the complementary systematics of the reduced $\alpha$-decay widths and nuclear $g$ factors of low-lying, $I^{\pi}=1/2^+$ states in the neutron-deficient lead region. The findings shed light on the unexpected hindrance of the $1/2^+ \rightarrow 1/2^+$ , $^{181}$Tl$^g \rightarrow ^{177}$Au$^g \alpha$ decay, which is explained by a mixing of $\pi 3 s_{1/2}$ and $\pi 2 d_{3/2}$ configurations in $^{177}$Au$^g$ , whilst $^{181}$Tl$^g$ remains a near-pure $\pi 3 s_{1/2}$. This conclusion is inferred from the $g$ factor of $^{177}$Au$^g$ which has an intermediate value between those of $\pi 3 s_{1/2}$ and $\pi 2 d_{3/2}$ states. A similar mixed configuration is proposed for the $I^{\pi} =1/2^+$ ground state of $^{179}$Au. This mixing may provide evidence for triaxial shapes in the ground states in these nuclei.

Mots clés: Nuclear physics; Decay spectroscopy; Laser spectroscopy; Nuclear deformation; Gold nuclei; Thallium nuclei

Domaines: Physique Nucléaire Expérimentale [nucl-ex]

J.G. Cubiss, A.E. Barzakh, A.N. Andreyev, M. Al Monthery, N. Althubiti, et al.. Change in structure between the $I = 1/2$ states in $^{181}$Tl and $^{177,179}$Au. Phys.Lett.B, 2018, 786, pp.355-363. ⟨10.1016/j.physletb.2018.10.005⟩. ⟨hal-01914550⟩