A search for mixed-symmetry states in the mass A approximately 50 region

Abstract

Mixed-symmetry 2' states are identified in vibrational-like nuclei lying between the 2 = 2 0 and 28 closed shells. The M1 strengths of 2t-2+ transitions are obtained from level lifetimes and y-ray multipole mixing ratios. The latter were measured using the directional distribution of y-rays from an oriented source (56Fe) and y y directional correlations on cascades which follow neutron capture ("Ti, "Cr and 58Fe). There is strong evidence for the sharing the characteristics of the mixed-symmetry 2t level with neighbouring 2+ levels. The identification of a 4+-4+ transition with a large B(M1) value in S6Fe indicates the need for g-bosons in the IBA-2 which is used as a framework for discussing the data. RADIOACTIVITY 56Mn(/?, Y ) ' ~F ~, cryogenically oriented nuclei; measured y(6); deduced 6. NUCLEAR REACTION 47Ti, 53Cr and "Fe (n, y ) ; enriched target, online directional correlations; measured yy(6); deduced 6.

Electroexcitation of magnetic dipole and other modes in46Ti and48Ti

“…Hence, as a first guess, one may conclude that any J==3 + state which we found in our spectra is a mixed symmetry state. If our further analysis will confirm these preliminary results, then, in the case of the first of these states, this would be in agreement with the analysis of Abdelaziz et al E42], see also [64]. Thus the state at Ex = 3.607 MeV could be the second J= = 3 + mixed symmetry state.…”

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

“…Shortly after the tentative identification [19] of 2 + 1,ms one-phonon MSSs of vibrational nuclei near the N = 82 neutron shell closure the mass region near the doubly closed shell 56 Ni was examined for vibrational MS structures [82,147]. Lifetime measurements and microscopic calculations generally corroborate the proposals of a one-phonon 2 + state with significant MS character.…”

“…Strong M1 transitions between low-energy 4 + states in near-closed-shell nuclei have already tentatively been interpreted in terms of symmetric and mixed-symmetry hexadecapole excitations [110,147]. The sd f -IBM-2 predicts [62] symmetrical and mixedsymmetry octupole vibrations and additionally an entire class of states that show a mixedsymmetric coupling of quadrupole and octupole parts that are each symmetrical individually.…”

“…These states are observed at about 3 MeV excitation energy, i.e., about 1 MeV higher than in the heavy vibrators. Already Collins et al [147] have therefore given the caveat that "It is possible that other types of excitation may be involved. For instance in the neighboring semi-magic nuclei, 52 Cr and 54 Fe, only proton bosons are present and so low-lying mixedsymmetry states are ruled out, although both nuclei have 2 + states at about 2 MeV which decay to the first 2 + state with B(M1) 0.1 µ 2 N ."…”

“…It decays predominantly to the 2 + 1 state by a pure M1 transition with an E2/M1 multipole mixing ratio of 0.02(5) [147] and with a strength of B(M1; 2 + 3 → 2 + 1 ) = 0.39(6) µ 2 N [31]. It dominates the 2 + → 2 + 1 M1 transition strength distribution and has, therefore, been interpreted [31,147] as the main fragment of the 2 + 1,ms onephonon MSS of 54 Cr. Shell model results mapped onto a boson model space [148] support mixedsymmetry character residing in low-lying 2 + states.…”