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6 pags., 5 figs., 1 tab. ; There is sparse direct experimental evidence that atomic nuclei can exhibit stable "pear" shapes arising from strong octupole correlations. In order to investigate the nature of octupole collectivity in radium isotopes, electric octupole (E3) matrix elements have been determined for transitions in Ra222,228 nuclei using the method of sub-barrier, multistep Coulomb excitation. Beams of the radioactive radium isotopes were provided by the HIE-ISOLDE facility at CERN. The observed pattern of E3 matrix elements for different nuclear transitions is explained by describing Ra222 as pear shaped with stable octupole deformation, while Ra228 behaves like an octupole vibrator. ; The support of the ISOLDE Collaboration and technical teams is acknowledged. This work was supported by the following Research Councils and Grants: Science and Technology Facilities Council (UK) Grants No. ST/P004598/1, No. ST/L005808/1, No. ST/ R004056/1; Federal Ministry of Education and Research (Germany) Grants No. 05P18RDCIA, No. 05P15PKCIA, and No. 05P18PKCIA and the "Verbundprojekt 05P2018"; National Science Centre (Poland) Grant No. 2015/18/M/ ST2/00523; European Union's Horizon 2020 Framework research and innovation programme 654002 (ENSAR2); Marie Skłodowska-Curie COFUND Grant (EU-CERN) 665779; Research Foundation Flanders and IAP Belgian Science Policy Office BriX network P7/12 (Belgium); GOA/2015/010 (BOF KU Leuven); RFBR (Russia) Grant No. 17-52-12015; and the Academy of Finland (Finland) Grant No. 307685.

6 pags., 4 figs., 1 tab. -- Open Access funded by Creative Commons Atribution Licence 4.0 ; The first 2(+) and 3(-) states of the doubly magic nucleus Sn-132 are populated via safe Coulomb excitation employing the recently commissioned HIE-ISOLDE accelerator at CERN in conjunction with the highly efficient MINIBALL array. The Sn-132 ions are accelerated to an energy of 5.49 MeV/nucleon and impinged on a Pb-206 target. Deexciting gamma rays from the low-lying excited states of the target and the projectile are recorded in coincidence with scattered particles. The reduced transition strengths are determined for the transitions 0(g.s)(+) -> 2(1)(+), 0(g.s)(+) -> 3(1)(-), and 2(1)(+) -> 3(1)(-) in Sn-132. The results on these states provide crucial information on cross-shell configurations which are determined within large-scale shell-model and Monte Carlo shell-model calculations as well as from random-phase approximation and relativistic random-phase approximation. The locally enhanced B(E2; 0(g.s)(+) -> 2(1)(+)) strength is consistent with the microscopic description of the structure of the respective states within all theoretical approaches. The presented results of experiment and theory can be considered to be the first direct verification of the sphericity and double magicity of Sn-132. ; The research leading to these results has received funding from the European Union's Horizon 2020 research and innovation program under Grant Agreement No. 654002. This work was supported by the German BMBF under Contract No. 05P15PKCIA and Verbundprojekt No. 05P2015, in part by the High Performance Computing Infrastructure Strategic Program (Grant No. hp150224), in part by MEXT and Joint Institute for Computational Fundamental Science and a priority issue (elucidation of the fundamental laws and evolution of the universe) to be tackled by using the Post "K" Computer (Grants No. hp160211 and No. hp170230), in part by the HPCI system research project (Grant No. hp170182), by the CNS-RIKEN joint project for large-scale nuclear-structure calculations, in part by the Spanish Ministry of Economy, Industry and Competitiveness through Project No. FPA2017-87568-P, by FWO-Vlaanderen (Belgium), by GOA/2010/010 (BOF KU Leuven), and by the Interuniversity Attraction Poles Programme initiated by the Belgian Science Policy Office (BriX network P7/12). A. V. and L. K. thank the Bonn-Cologne Graduate School of Physics and Astronomy for financial support. J. P. and D. M. C. acknowledge the Academy of Finland (Contract No. 265023). G. R. acknowledges support by Bulgarian National Science Fund under Grant No. DN08/23/16. L. P. G. has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska- Curie Grant Agreement No. 665779. ; Peer Reviewed

19 pags., 11 figs., 3 tabs. ; The high-spin structures of Ba136 and Ba137 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Ba136 is populated in a Xe136+U238 MNT reaction employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy, and in two Be9+Te130 fusion-evaporation reactions using the High-efficiency Observatory for γ-Ray Unique Spectroscopy (HORUS) at the FN tandem accelerator of the University of Cologne, Germany. Furthermore, both isotopes are populated in an elusive reaction channel in the B11+Te130 fusion-evaporation reaction utilizing the HORUS γ-ray array. The level scheme above the Jπ=10+ isomer in Ba136 is revised and extended up to an excitation energy of approximately 5.5 MeV. From the results of angular-correlation measurements, the Ex=3707- and Ex=4920-keV states are identified as the bandheads of positive- and negative-parity cascades. While the high-spin regimes of both Te132 and Xe134 are characterized by high-energy 12+→10+ transitions, the Ba136E2 ground-state band is interrupted by negative-parity states only a few hundred keV above the Jπ=10+ isomer. Furthermore, spins are established for several hitherto unassigned high-spin states in Ba137. The new results close a gap along the high-spin structure of N<82 Ba isotopes. Experimental results are compared to large-scale shell-model calculations employing the GCN50:82, Realistic SM, PQM130, and SN100PN interactions. The calculations suggest that the bandheads of the positive-parity bands in both isotopes are predominantly of proton character. ; Furthermore, we express our thanks to Dr. E. Teruya and Dr. N. Yoshinaga from Saitama University, Japan, for providing the results of their shellmodel calculation with the PQM130 interaction. The research leading to these results has received funding from the German BMBF under Contracts No. 05P15PKFN9 TP1 and No. 05P18PKFN9 TP1, from the European Union Seventh Framework Programme FP7/2007-2013 under Grant Agreement No. 262010 - ENSAR, from the Spanish Ministerio de Ciencia e Innovación under Contract No. FPA2011-29854- C04, from the Spanish Ministerio de Economía y Competitividad under Contract No. FPA2014-57196-C5, and from the UK Science and Technology Facilities Council (STFC). L.K. and A.V. thank the Bonn-Cologne Graduate School of Physics and Astronomy (BCGS) for financial support. One of the authors (A. Gadea) has been supported by the Generalitat Valenciana, Spain, under Grant No. PROMETEOII/2014/019, and EU under the FEDER program.

6 pags., 4 fig.s, 1 tab. -- Open Access funded by Creative Commons Atribution Licence 4.0 ; There is a large body of evidence that atomic nuclei can undergo octupole distortion and assume the shape of a pear. This phenomenon is important for measurements of electric-dipole moments of atoms, which would indicate CP violation and hence probe physics beyond the Standard Model of particle physics. Isotopes of both radon and radium have been identified as candidates for such measurements. Here, we observed the low-lying quantum states in Rn and Rn by accelerating beams of these radioactive nuclei. We show that radon isotopes undergo octupole vibrations but do not possess static pear-shapes in their ground states. We conclude that radon atoms provide less favourable conditions for the enhancement of a measurable atomic electric-dipole moment. ; The support of the ISOLDE Collaboration and technical teams is acknowledged. This work was supported by the following Research Councils and Grants: Science and Technology Facilities Council (STFC; UK) grants ST/ P004598/1, ST/L005808/1; Federal Ministry of Education and Research (BMBF; Germany) grants 05P18RDCIA, 05P15PKCIA and 05P18PKCIA and the "Verbundprojekt 05P2018"; National Science Centre (Poland) grant 2015/18/M/ST2/00523; European Union's Horizon 2020 Framework research and innovation programme 654002 (ENSAR2); Marie Skłodowska-Curie COFUND grant (EU-CERN) 665779; Research Foundation Flanders (FWO, Belgium), by GOA/2015/010 (BOF KU Leuven) and the Interuniversity Attraction Poles Programme initiated by the Belgian Science Policy Office (BriX network P7/12); RFBR(Russia) grant 17-52-12015.