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

Abstract 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 126 Sn nucleus. The nucleus was produced by the fission of a relativistic 238 U 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 ν ( h 11 / 2 − 1 d 3 / 2 − 1 ) 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 132 Sn is discussed. The first observation of 18(8)% of spin-alignment produced by the relativistic fission of a 238 U beam paves the way to study moments of neutron-rich (sub-)microsecond isomers, which are difficult to align by other means.