E2 decay strength of the M1 scissors mode of Gd156

Abstract

E 2 decay strength of the M 1 scissors mode of The E2/M 1 multipole mixing ratio δ1→2 of the 1 + sc → 2 + 1 γ-ray decay in 156 Gd and hence the isovector E2 transition rate of the scissors mode of a well-deformed rotational nucleus has been measured for the first time. It has been obtained from the angular distribution of an artificial quasimonochromatic linearly polarized γ-ray beam of energy 3.07(6) MeV scattered inelastically off an isotopically highly-enriched 156 Gd target. The data yield first direct support for the deformation dependence of effective proton and neutron quadrupole boson charges in the framework of algebraic nuclear models. First evidence for a low-lying J π = 2 + member of the rotational band of states on top of the 1 + band head is obtained, too, indicating a significant signature splitting in the K = 1 scissors mode rotational band.Introduction. -Orbital out-of-phase oscillations of a coupled two-component many-body quantum system are generally called Scissors Modes (ScMs). A ScM has been discovered in deformed atomic nuclei [1]. It has later been identified in Bose-Einstein condensed gases [2,3] and is expected to occur in Fermi gases [4], in metallic clusters [5][6][7], and in deformed quantum dots [8]. ScMs are interesting quantum modes because their properties are sensitive to the restoring forces between the many-body subsystems. They inevitably break spherical symmetry and hence lead to a sequence of quantum states of the many-body system that form a rotational band.

Investigation ofJ=1states and theirγ-decay behavior inCr52

“…Detailed information can be found, e.g., in Refs. [40,41]. The photon flux distribution of the γ-ray beam was directly measured with a 123% HPGe detector (beam detector) that can be moved in the beam line behind the γ 3 setup.…”

Probing the E2 properties of the scissors mode with real photons

“…Hence, further constraints based on the comparison of experimental decay intensity ratios to expectations from the Alaga rule [16] are needed to identify [6] the consistent solution for the multipole mixing ratio.…”

“…The results of the pioneering experiment on 156 Gd are presented in detail elsewhere [6]. In the following, the robustness of the method towards systematic uncertainties shall be addressed.…”

“…therein]. Despite the quadrupole-collective origin of the nuclear scissors mode, the E2 properties of the scissors mode were unknown until recently [6]. Likewise, information on the predicted existence of the scissors mode's rotational band with the J = 1 state as band head is limited [7,8].…”

“…Likewise, information on the predicted existence of the scissors mode's rotational band with the J = 1 state as band head is limited [7,8]. First information on the E2 decay transition strength of the scissors mode was extracted [6] from a highstatistics photon-scattering experiment on 156 Gd using quasi-monochromatic photon beams provided by the High Intensity γ-ray Source (HIγS) [9] at Duke University, Durham, NC, USA. The data allowed for measuring a finite value of the E2/M1 multipole mixing ratio and, thus, first measurement of an E2 transition between mixedsymmetric and a fully-symmetric states in axially deformed nuclei.…”