Speaker
Description
The neutron-rich transitional nuclei with $A\sim190$ demonstrate a shape transition from well-deformed to $\gamma$-soft structures with increasing neutron number [1]. Some of the nuclei in this region have been well studied in previous experimental investigations of nuclear masses, nuclear structure, and transitions, as summarized in a recent review paper [2].
Recently, the use of multi-nucleon transfer reactions at KEK Isotope Separation System (KISS) [3] in RIKEN have enabled us to expand multi-faceted nuclear spectroscopy in this region via decay spectroscopy of $^{187}$Ta [4] and mass spectroscopy of $^{189}$W, $^{192}$Re using a MRTOF-MS [5]. In this work, the decay scheme of $^{187}$Ta has been newly established, connecting previously known $\gamma$-transitions in $^{187}$W. The masses of $^{189}$W and $^{192}$Re were successfully measured, and the trend of the two-neutron separation energies for neutron-rich W and Re isotopes was interpreted based on DFT calculations, suggesting that shape transitions from prolate deformation begin at $N = 116$ and $N = 117$ in the W and Re isotopic chains, respectively, consistent with previous studies.
In this talk, we will introduce the details of the experiments and discuss the above experimental results.
References:
[1] R. F. Casten, Nucl. Phys. A 443, 1 (1985).
[2] G. G. Kiss and Z. Podolyák, Eur. Phys. J. A 60, 175 (2024).
[3] Y. Hirayama et al., Nucl. Inst. Meth. B 353, 4 (2015), and B 412, 11 (2017).
[4] M. Mukai et al., Phys. Rev. C 105, 032331 (2022).
[5] M. Mukai et al., Phys. Rev. C, accepted for publication.
