Identification of the one-quadrupole phonon 21,ms+ state of 204Hg

• Main Authors: R. Stegmann, C. Stahl, G. Rainovski, N. Pietralla, C. Stoyanov, M.P. Carpenter, R.V.F. Janssens, M. Lettmann, T. Möller, O. Möller, V. Werner, S. Zhu
• Format: Article
• Language: English
• Published: Elsevier 2017-07-01
• Series: Physics Letters B
• Subjects: γ ray spectroscopy; Coulomb excitation; Quadrupole collectivity; Isospin degree of freedom; Shell structure
• Online Access: http://www.sciencedirect.com/science/article/pii/S0370269317303064
• ISSN: 0370-2693; 1873-2445

One-phonon states of vibrational nuclei with mixed proton–neutron symmetry have been observed throughout the nuclear chart besides the mass A≈200 region. Very recently, it has been proposed that the 22+ state of 212Po is of isovector nature. This nucleus has two valence protons and two valence neutrons outside the doubly-magic 208Pb nucleus. The stable isotope 204Hg, featuring two valence-proton and valence-neutron holes, with respect to 208Pb, is the particle-hole mirror of 212Po. In order to compare the properties of low-lying isovector excitations in these particle-hole mirror nuclei, we have studied 204Hg by using the projectile Coulomb-excitation technique. The measured absolute B(M1;22+→21+) strength of 0.20(2)μN2 indicates that the 22+ level of 204Hg is at least the main fragment of the 21,ms+ state. For the first time in this mass region, both lowest-lying, one-quadrupole phonon excitations are established together with the complete set of their decay strengths. This allows for a microscopic description of their structures, achieved in the framework of the Quasi-particle Phonon Model.