T-REX: A new setup for transfer experiments at REX-ISOLDE

Transfer reactions in inverse kinematics using the radioactive ion beams provided by the REXISOLDE facility at CERN are very good tools to gain insight into the single-particle properties of exotic nuclei. The new silicon particle detector setup T-REX, optimized for these transfer reactions, is presented in this article. T-REX consists of position sensitive ΔE-E telescopes in a compact configuration that covers up to 66% of the solid angle. The setup allows the identification of the light reaction products and the measurement of their angular distribution for a large range of polar angles. Simultaneous detection of the elastically scattered target-like nuclei enables the determination of the optical model parameters used in the analysis of the experiments.status: publishe

Prolate shape of 140Ba from a first combined Doppler-shift and Coulomb-excitation measurement at the REX-ISOLDE facility

Background: Quadrupole moments of excited nuclear states are important observables for geometrically interpreting nuclear structure in terms of deformed shapes, although data are scarce and sometimes ambiguous, in particular, in neutron-rich nuclides. Purpose: A measurement was performed for determining the spectroscopic quadrupole moment of the 2+1 state of 140Ba in order to clarify the character of quadrupole deformation (prolate or oblate) of the state in its yrast sequence of levels. Method:We have utilized a new combined technique of lifetime measurement at REX-ISOLDE and MINIBALL using the Doppler-shift attenuation method (DSAM) and a reorientation analysis of Coulomb-excitation yields. Results: On the basis of the new lifetime of τ (2+1 ) = 10.4+2.2−0.8 ps the electric quadrupole moment was determined to be Q(2+1 ) = −0.52(34) eb, indicating a predominant prolate deformation. Conclusions: This finding is in agreement with beyond-mean-field calculations using the Gogny D1S force and with results from the Monte Carlo shell-model approach.status: publishe

Coulomb excitation of the 3− isomer in 70Cu

Post-accelerated isomerically purified radioactive beams, available at the CERN On-Line Isotope Mass Separator facility using the resonant ionization laser technique, have been used to study the Coulomb excitation of the I π = 3− state in 70Cu (Z = 29, N = 41). While first results using a I π = 6− beam were reported previously, the present complementary experiment allows us to complete the study of the multiplet of states (3−, 4−, 5−, 6−) arising from the π2p3/2ν1g9/2 configuration. Besides the known γ -ray transition deexciting the 4− state, a ground-state γ ray of 511(3) keV was observed for the first time and was unambiguously associated with the 5− state deexcitation. This observation fixes the energy, spin, and parity of this state, completing the low-energy level scheme of 70Cu. B(E2) values for all possible E2 transitions within the multiplet were determined. A comparison with large-scale shell model calculations using different interactions and valence spaces shows the importance of proton excitation across the Z = 28 shell gap and the role of the 2d5/2 neutron orbital.status: publishe