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

• Published in: Physics letters. B Vol. 770; no. C; pp. 77 - 82
• Main Authors: Stegmann, R., Stahl, C., Rainovski, G., Pietralla, N., Stoyanov, C., Carpenter, M.P., Janssens, R.V.F., Lettmann, M., Möller, T., Möller, O., Werner, V., Zhu, S.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 10-07-2017; Elsevier
• Subjects: Coulomb excitation; Isospin degree of freedom; Quadrupole collectivity; Shell structure; γ ray spectroscopy; Isospin degree of freedom; Shell structure; Coulomb excitation; γ ray spectroscopy; Quadrupole collectivity
• ISSN: 0370-2693; 1873-2445
• DOI: 10.1016/j.physletb.2017.04.032

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.