Quadrupole collectivity in Ca 42 from low-energy Coulomb excitation with AGATA

A Coulomb-excitation experiment to study electromagnetic properties of Ca42 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 Ca42 were measured with the AGATA spectrometer. The magnitudes and relative signs of ten E2 matrix elements coupling six low-lying states in Ca42, including the diagonal E2 matrix elements of 21+ and 22+ 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 01,2+ and 21,2+ states, as well as triaxiality for 01,2+ states, establishing the coexistence of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in Ca42. 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 Ca42

Collectivity and single-particle degrees of freedom

Intruder rotational bands in 45 Sc and 45 Ti have been investigated up to the maximum aligned angular momentum by means of EUROBALL IV and the Recoil Filter Detector (RFD). The use of the RFD allowed for a reduction of the $\gamma$-line Doppler broadening and, moreover, for a determination of very short level lifetimes. In the studied nuclei, the estimated deformation shows a gradual disappearance of the collectivity at the highest available spins

High spin states in 45Sc and coexistence of collective and non-collective structures in the odd-A nuclei

High-spin states in 43Ca, 45Sc, and 45Ti were studied with the GASP multidetector array coupled with the Recoil Mass Spectrometer. The nuclei were excited in the 60 MeV 18O +30Si reaction. Lifetimes were extracted from the analysis of the Doppler-shift attenuation of γ-rays observed in the reversed 35Cl+12C reaction. The lifetimes, B(M1) and B(E2) values for 45Sc are presented. The measurements suggest significant deformation of the positive-parity intruder band in this nucleus. The band is predicted by the mean-field calculations to be the cross-shell particle-hole excitation associated with a strong quadrupole core-polarization. Spherical shell-model calculations reproduce observed excitation energies and transition rates in both spherical and deformed structures

Rare Isotopes Investigation at GSI (RISING) using Gamma-ray Spectroscopy at Relativistic Energies

The Rare ISotopes INvestigation at GSI project combines the former EUROBALL Ge-Cluster detectors, the MINIBALL Ge detectors, BaF2--HECTOR detectors, and the fragment separator at GSI for high-resolution in-beam gamma-ray spectroscopy measurements with radioactive beams. These secondary beams produced at relativistic energies are used for Coulomb excitation or secondary fragmentation experiments in order to explore the nuclear structure of the projectiles or projectile like nuclei by measuring de-excitation photons. The newly designed detector array is described and the performance characteristics are given. Moreover, particularities of the experimental technique are discussed