Mixed-symmetry states and the structure of²⁰⁰Hg

Abstract

Mixed-symmetry assignments are made to the 1.570 (l;), 1.573 (2:) and 1.659 (3:) MeV levels in 2wHg. The characteristics of the 2: level are shared with nearby 2+ levels at 1.254 and 1.593 MeV. An interacting boson approximation (IBA-2) analysis examines the sensitivity of the mixed-symmetry states to the E, parameters of the Majorana term and finds that both the magnitude and sign of the d(E2iM1) mixing ratio of 2' -2: transitions are well reproduced at the values of the tt parameters used to obtain a level energy fit. The IBA-2 calculations also give a satisfactory fit to the energy levels and in general provide X(EOiE2) values close to the experimental data. These calculations agree with the known oblate deformation of the ground state which we find to be predicted by Kumar's dynamic deformation model.Experimental data from n, yy(0) experiments together with internal conversion coefficient (ICC) results allow 1+ levels to be unambiguously established at 1.570, 1.631, 1.718, 2.061, 2.370, 2.640 and 2.979 MeV. The measurements also provide precise 6 values of many transitions while event-by-event coincidence information permits the decay scheme to the developed with previous unlocated transitions now firmly assigned. NUCLEAR REACTIONS '99Hg(n; y)ZWHg; thermal neutrons, measured I,, y-ray coincidences, yy(8); deduced 6(E2/Ml), X(EOIE2), mixed-symmetry states, level scheme; enriched target, Ge(Li) detectors. 3 3 0

Experiments on multiphonon states with proton–neutron mixed symmetry in vibrational nuclei

“…Eq. (22) shows that the 2 + 1,ms state is a one-phonon excitation which has proton and neutron E2 excitation matrix elements of about the same size as those of the 2 + 1 state. Due to the destructive interference between the proton and neutron E2 matrix elements, the total E2 strength of excitation to the 2 + 1,ms is reduced in comparison to that of the 2 + 1 state.…”

“…of Eq. (22) is completely exhausted by the space of states with quantum number F = F max − 1. The d-parity quantum number which will be discussed below ensures in conjunction with τ selection rules of the quadrupole operator the validity of the Eqs.…”

“…Similar arguments were subsequently used by several authors, e.g., in Refs. [20][21][22][23][24] and others, for the assignment of mixed-symmetry character to off-yrast low-spin states of vibrational and transitional nuclei in different mass regions. Other approaches made use of the isospin sensitivity of hadronic probes for the assignment of MSSs [25][26][27].…”

Low-energy nuclear spectroscopy in a microscopic multiphonon approach

“…Its first evidence was inferred from the analysis of the E2/M1 mixing and branching ratios in N = 84 isotones [71]. Several subsequent works have guessed the mixed-symmetry character of low-spin states in vibrational and transitional nuclei on the ground of similar arguments [72][73][74][75][76] or by exploiting the sensitivity of the probe to isospin [77][78][79][80]. A more reliable assessment of the mixed-symmetry nature of 2 + states could be made after the measurements of absolute electromagnetic decay strengths [81][82][83][84][85][86][87][88][89].…”

Proton-Neutron Mixed-Symmetry3ms+State inM94Pietralla1, Fransen2, Brentano3 et al. 2000Phys. Rev. Lett.859830View full textAdd to dashboardCite

“…In some cases E2͞M1 mixing ratios were used to tentatively assign MS character to nuclear states with J . 2, e.g., [15,16]. However, the M1 strengths were not measured, rendering the MS assignments uncertain.…”