Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Seidlitz, M., Muecher, D., Reiter, P., Bildstein, V., Blazhev, A., Bree, N., ... Wiens, A. (2011). Coulomb excitation of , 181-186. https://doi.org/10.1016/j.physletb.2011.05.009 Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date: 11-04-2019Physics Letters B 700 (2011) © 2011 Elsevier B.V. All rights reserved. MotivationShell structure is one of the most important frameworks for understanding nuclear structure and the properties of atomic nuclei. Recent experimental and theoretical findings indicate that magic numbers are subject to the proton-to-neutron ratio and new magic numbers are revealed when going to more exotic nuclei. Such a new magic number was proposed at N = 16 for some nuclei be- ground state for these nuclei [6]. Later shell model calculations by Warburton et al. [7] showed that the 1 f 7/2 orbital becomes lower in energy, reducing the sd shell gap and an anomalous inverted level structure was proposed, which is based on 2-particle 2-hole (2p2h) neutron cross shell configurations in the ground state. ExperimentThe Coulomb excitation experiment was performed at the REX-ISOLDE facility at CERN [37,38] The scattered beam and recoiling target nuclei were detected by a CD-shaped 500 μm thick double sided silicon strip detector (DSSSD), consisting of four identical quadrants [40]. Each quadrant comprised 16 annular strips at the front side and 24 radial strips at the back side for identification and reconstruction of the trajectories of the scattered nuclei. The detector covered forward angles between 16.4 • and 53.3 • in the laboratory system. De-excitation γ -rays following Coulomb excitation of projectile and target nuclei were detected by the MINIBALL γ -spectrometer, consisting of eight triple cluster detectors in close geometry, each containing three 6-fold segmented HPGe crystals [41]. The photopeak efficiency of the array at 1.3 MeV was 8% after cluster addback. The high segmentation of the setup ensured a proper Doppler correction for in-flight γ -ray emission at v/c ∼ 8% by combining the angular information of the γ -ray with the direction and velocity of the scattered beam particle that was detected in coincidence.Two additional particle detectors were used downstream after the scattering chamber to monitor the position of the beam and M. Seidlitz et al. / Physics Letters B ...

Many-body nuclear theory utilizing microscopic or chiral potentials has developed to the point that collectivity might be dealt with in an ab initio framework without the use of effective charges; for example with the proper evolution of operators, or alternatively, through the use of an appropriate and manageable subset of particle-hole excitations.We present a precise determination of E2 strength in 22 Mg and its mirror 22 Ne by Coulomb excitation, allowing for rigorous comparisons with theory. No-core symplectic shell-model calculations were performed and agree with the new B(E2) values while in-medium similarity-renormalization-group calculations consistently underpredict the absolute strength, with the missing strength found to have both isoscalar and isovector components.

The island of inversion for neutron-rich nuclei in the vicinity of N = 20 has become the testing ground par excellence for our understanding and modeling of shell evolution with isospin. In this context, the structure of the transitional nucleus 29 Mg is critical. The first quantitative measurements of the single-particle structure of 29 Mg are reported, using data from the d (28 Mg, p γ) 29 Mg reaction. Two key states carrying significant = 3 (f-wave) strength were identified at 2.40 ± 0.10 (J π = 5/2 −) and 4.28 ± 0.04 MeV (7/2 −). New state-of-the-art shell-model calculations have been performed and the predictions are compared in detail with the experimental results. While the two lowest 7/2 − levels are well described, the sharing of single-particle strength disagrees with experiment for both the 3/2 − and 5/2 − levels and there appear to be general problems with configurations involving the p 3/2 neutron orbital and core-excited components. These conclusions are supported by an analysis of the neutron occupancies in the shell-model calculations.

International audienceBackground: Shape coexistence in heavy nuclei poses a strong challenge to state-of-the-art nuclear models, where several competing shape minima are found close to the ground state. A classic region for investigating this phenomenon is in the region around Z=82 and the neutron mid-shell at N=104.Purpose: Evidence for shape coexistence has been inferred from α-decay measurements, laser spectroscopy and in-beam measurements. While the latter allow the pattern of excited states and rotational band structures to be mapped out, a detailed understanding of shape coexistence can only come from measurements of electromagnetic matrix elements.Method: Secondary, radioactive ion beams of 202Rn and 204Rn were studied by means of low-energy Coulomb excitation at the REX-ISOLDE facility in CERN.Results: The electric-quadrupole (E2) matrix element connecting the ground state and first-excited 2+1 state was extracted for both 202Rn and 204Rn, corresponding to B(E2;2+1→2+1)=29+8−8 W.u. and 43+17−12 W.u., respectively. Additionally, E2 matrix elements connecting the 2+1 state with the 4+1 and 2+2 states were determined in 202Rn. No excited 0+ states were observed in the current data set, possibly due to a limited population of second-order processes at the currently-available beam energies.Conclusions: The results are discussed in terms of collectivity and the deformation of both nuclei studied is deduced to be weak, as expected from the low-lying level-energy schemes. Comparisons are also made to state-of-the-art beyond-mean-field model calculations and the magnitude of the transitional quadrupole moments are well reproduced