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

Abstract

Available online xxxx Editor: V. Metag Keywords: γ ray spectroscopy Coulomb excitation Quadrupole collectivity Isospin degree of freedom Shell structureOne-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 2 + 2 state of 212 Po is of isovector nature. This nucleus has two valence protons and two valence neutrons outside the doubly-magic 208 Pb nucleus. The stable isotope 204 Hg, featuring two valence-proton and valence-neutron holes, with respect to 208 Pb, is the particle-hole mirror of 212 Po. In order to compare the properties of low-lying isovector excitations in these particle-hole mirror nuclei, we have studied 204 Hg by using the projectile Coulomb-excitation technique. The measured absolute B(M1; 2 +strength of 0.20 (2) μ 2 N indicates that the 2 + 2 level of 204 Hg is at least the main fragment of the 2 + 1,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.

Search for Isovector Valence-Shell Excitations in 140Nd and 142Sm via Coulomb excitation reactions of radioactive ion beams

“…Prominent examples are found in the mass A=90 region. Several cases are reported in the mass A=130 region and recently three cases are found in the mass A=208 region [10][11][12]. It is observed, that the even-even N=80 isotones form isolated proton-neutron mixed-symmetry 2 + 1,ms states from Z=52 to Z=56 [13][14][15].…”

Nuclear isovector valence-shell excitation of Hg202

“…One-quadrupole-phonon MSSs were identified all across the nuclear chart; in the mass A ≈ 90 region [6,12,13], as well in the mass A ≈ 130 region [14][15][16][17][18][19] and, most recently, in the mass A ≈ 200 region [20,21]. The experimental information accumulated up to now suggests that pronounced one-phonon MSSs can be expected when both protons and neutrons occupy orbitals with high angular momenta as in the case of 212 Po [20].…”

“…The experimental information accumulated up to now suggests that pronounced one-phonon MSSs can be expected when both protons and neutrons occupy orbitals with high angular momenta as in the case of 212 Po [20]. However, 204 Hg offers an opposite example -even though its valence structure is dominated by orbitals with small angular momenta for both protons and neutrons, 204 Hg exhibits a 2 + 1,ms state with an even larger M 1 decay strength than in 212 Po [20,21]. 202 Hg exhibits a similar valence structure as 204 Hg, but with two additional neutron holes.…”

“…The technique is described in Ref. [21] and is based on fitting, with the Coulomb excitation code GOSIA [41], transition matrix elements for a subset of states to Coulomb cross sections; e.g., the 2 + level of interest, the most populated 3 − state, the 2 + 1 level and the ground state. The only free parameter in this procedure is the E2/M 1 multipole mixing ratio of the 2 + → 2 + 1 transition being considered.…”