[Paper] g factor of the 7⁻ isomer in ¹²⁶Sn and first observation of spin-alignment in relativistic fission

g factor of the 7⁻ isomer in ¹²⁶Sn and first observation of spin-alignment in relativistic fission

G. Ilie, G. Neyens, G.S. Simpson, J. Jolie, A. Blazhev, H. Grawe, R.L. Lozeva, N. Vermeulen, L. Atanasova, D.L. Balabanski, F. Becker, P. Bednarczyk, C. Brandau, L. Caceres, S.K. Chamoli, J.M. Daugas, P. Doornenbal, J. Gerl, M. Górska, J. Grebosz, M. Hass, M. Ionescu-Bujor, A. Jungclaus, M. Kmiecik, I. Kojouharov, N. Kurz, A. Maj, S. Mallion, O. Perru, M. Pfützner, Zs. Podolyák, W. Prokopowicz, M. De Rydt, T.R. Saito, H. Schaffner, K. Turzó, J. Walker, E. Werner-Malento and H.J. Wollersheim

doi:10.1016/j.physletb.2010.03.033

We report on the g factor measurement of the isomeric 7⁻ state (E*=2219 keV, T_1/2=5.9(8) μs) in the neutron-rich ¹²⁶Sn nucleus. The nucleus was produced by the fission of a relativistic ²³⁸U beam and reaction products were selected by the FRS fragment separator at GSI. For the first time, spin-alignment was observed after relativistic fission. It was used to deduce the g factor of the 7⁻ isomeric state, g(7⁻)=−0.098(9), from the measured perturbed angular distribution of its γ decay using the RISING Cluster detectors. The observed value confirms the suggested source dominant configuration, which has been proposed for the 7⁻ isomers in neutron-rich Sn isotopes. The failure of the g factor additivity rule and the importance of core polarization evolution with increasing distance from the doubly-magic ¹³²Sn is discussed. The first observation of 18(8)% of spin-alignment produced by the relativistic fission of a ²³⁸U beam paves the way to study moments of neutron-rich (sub-)microsecond isomers, which are difficult to align by other means.