Quadrupole collectivity in Ca42 from low-energy Coulomb excitation with AGATA

Abstract

K. HADYŃSKA-KLȨK et al. PHYSICAL REVIEW C 97, 024326 (2018) A Coulomb-excitation experiment to study electromagnetic properties of 42 Ca was performed using a 170-MeV calcium beam from the TANDEM XPU facility at INFN Laboratori Nazionali di Legnaro. γ rays from excited states in 42 Ca were measured with the AGATA spectrometer. The magnitudes and relative signs of ten E2matrix elements coupling six low-lying states in 42 Ca, including the diagonal E2 matrix elements of 2 + 1 and 2 + 2 states, were determined using the least-squares code GOSIA. The obtained set of reduced E2 matrix elements was analyzed using the quadrupole sum rule method and yielded overall quadrupole deformation for 0 + 1,2 and 2 + 1,2 states, as well as triaxiality for 0 + 1,2 states, establishing the coexistence of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in 42 Ca. The experimental results were compared with the state-of-the-art large-scale shell-model and beyond-mean-field calculations, which reproduce well the general picture of shape coexistence in 42 Ca.

Onset of triaxial deformation in Zn66 and properties of its first excited 0+ state studied by means of Coulomb excitation

“…7(a)]. Instead, the presently extracted value is close to those observed in 64 Zn and 68 Zn, which indicate a moderately collective character of the 2 2 + states. The relatively large uncertainties for the transitions depopulating the 2 2 + state reflect strong correlations of the corresponding matrix elements with the Q s (2 1 + ) value (observed also in Ref.…”

“…A systematic discrepancy between the values obtained in Coulomb-excitation and electron-scattering experiments is apparent from Fig. 6, particularly regarding the sign of the Q s (2 1 + ) [negative for 64,66,68 Zn from (e, e ) measurements, while positive for 66,68 Zn and compatible with zero in 64 rotor, assuming K = 2 for the 2 2 + state. Although a rotational interpretation may not be the most appropriate for the 66 Zn isotope, it is worth noticing that the signs of spectroscopic quadrupole moments deduced from the present analysis agree with it, supporting a positive sign of Q s (2 1 + ).…”

“…Being located only two protons above the reported in the Zn isotopic chain. The only exception is 68 Zn, where the 0 2 + state has been suggested to be the bandhead of a more deformed structure than that built on the ground state [6]. A shape transition from the almost spherical nuclei near 70 Zn (N = 40 subshell closure) to the γ -soft lighter Zn isotopes has also been predicted [7,8], although firm experimental evidence supporting this scenario is still missing.…”

Quadrupole deformation of Xe130 measured in a Coulomb-excitation experiment

“…The contribution of the individual matrix elements to the final values of Q 2 is shown. The Q 2 invariant is formed by summing all the contributions and by multiplying the sum by 1 and by −0.873 for cos(3δ) [41,57]. The loops containing transitional matrix elements are included twice in the contribution to the cos(3δ) invariant as their zero-coupled products can be formed in two possible ways.…”

“…In order to extract information on the charge distribution of the nucleus in specific states from the measured E 2 matrix elements, the quadrupole sum rules method [18,[55][56][57] can be used. This method is based on the fact that the electric multipole transition operator E (λ = 2, μ) is a spherical tensor and can be represented using two parameters: Q, the overall quadrupole deformation parameter equivalent to the elongation parameter β in Bohr's model, and δ, which is related to the triaxiality parameter γ .…”