Collective Motion in ¹³⁰Ba

An in-beam \rm\gamma spectroscopic study, based on the XTU Tandem accelerator of the Laboratori Nazionali di Legnaro in Italy, has been performed to explore the collective motion in ¹³⁰Ba. A significantly extended level scheme of ¹³⁰Ba has been built in the present work. High-spin states of ¹³⁰Ba were populated via the ¹²²Sn(¹³C, 5n) reaction at a beam energy of 65 MeV. The \rm\gamma rays were detected by the GALILEO spectrometer, while the neutrons and charged particles were detected by the Neutron Wall array and the EUCLIDES silicon apparatus, respectively. A series of new rotational bands in ¹³⁰Ba have been identified, among which there is a new structure populating to the previously known 9.4 ms isomer. With the help of previously reported intrinsic quadrupole moment and magnetic moment, we extracted precise value of the g factors of this isomer. According to the band structure analysis, the coexistence of prolate and oblate shapes has been observed in ¹³⁰Ba, while the orientation of collective rotation can be either along or away from the principal axes. It is the first time to identify a tilted band in the A = 130 mass region. Theoretical analysis suggests that a new band can be interpreted as the wobbling motion built on two-quasiparticle configuration, which is the first wobbling band observed in an even-even nucleus.