Showing papers by "R. F. Garcia Ruiz published in 2016"

Unexpectedly large charge radii of neutron-rich calcium isotopes

Abstract: Despite being a complex many-body system, the atomic nucleus exhibits simple structures for certain ‘magic’ numbers of protons and neutrons. The calcium chain in particular is both unique and puzzling: evidence of doubly magic features are known in 40,48Ca, and recently suggested in two radioactive isotopes, 52,54Ca. Although many properties of experimentally known calcium isotopes have been successfully described by nuclear theory, it is still a challenge to predict the evolution of their charge radii. Here we present the first measurements of the charge radii of 49,51,52Ca, obtained from laser spectroscopy experiments at ISOLDE, CERN. The experimental results are complemented by state-of-the-art theoretical calculations. The large and unexpected increase of the size of the neutron-rich calcium isotopes beyond N = 28 challenges the doubly magic nature of 52Ca and opens new intriguing questions on the evolution of nuclear sizes away from stability, which are of importance for our understanding of neutron-rich atomic nuclei. Doubly magic atomic nuclei — having a magic number of both protons and neutrons — are very stable. Now, experiments revealing unexpectedly large charge radii for a series of Ca isotopes put the doubly magic nature of the 52Ca nucleus into question.

Isomer Shift and Magnetic Moment of the Long-Lived 1/2$^+$ Isomer in $^{79}_{30}$Zn$_{49}$: Signature of Shape Coexistence near $^{78}$Ni

Abstract: Collinear laser spectroscopy has been performed on the $^{79}_{30}$Zn$_{49}$ isotope at ISOLDE-CERN. The existence of a long-lived isomer with a few hundred milliseconds half-life was confirmed, and the nuclear spins and moments of the ground and isomeric states in $^{79}$Zn as well as the isomer shift were measured. From the observed hyperfine structures, spins $I = 9/2$ and $I = 1/2$ are firmly assigned to the ground and isomeric states. The magnetic moment $\mu$ ($^{79}$Zn) = $-$1.1866(10) $\mu_{\rm{N}}$, confirms the spin-parity $9/2^{+}$ with a $ u g_{9/2}^{-1}$ shell-model configuration, in excellent agreement with the prediction from large scale shell-model theories. The magnetic moment $\mu$ ($^{79m}$Zn) = $-$1.0180(12) $\mu_{\rm{N}}$ supports a positive parity for the isomer, with a wave function dominated by a 2h-1p neutron excitation across the $N = 50$ shell gap. The large isomer shift reveals an increase of the intruder isomer mean square charge radius with respect to that of the ground state: $\delta \langle r^{2}_{c}\rangle^{79,79m}$ = +0.204(6) fm$^{2}$, providing first evidence of shape coexistence.

Isomer Shift and Magnetic Moment of the Long-Lived 1 / 2 + Isomer in Zn 49 30 79 : Signature of Shape Coexistence near Ni 78

Abstract: Two different experiments observe nuclei with excited nuclear states that differ in shape from their ground states, so called shape coexistence. These nuclei lie close to the neutron-rich doubly-magic ${}^{78}$Ni region of the nuclear chart.

Changes in nuclear structure along the Mn isotopic chain studied via charge radii

Abstract: The hyperfine spectra of $^{51,53\ensuremath{-}64}\mathrm{Mn}$ were measured in two experimental runs using collinear laser spectroscopy at ISOLDE, CERN. Laser spectroscopy was performed on the atomic $3{d}^{5}\phantom{\rule{4pt}{0ex}}4{s}^{2}\phantom{\rule{4pt}{0ex}}^{6}S_{5/2}\ensuremath{\rightarrow}3{d}^{5}\phantom{\rule{4pt}{0ex}}4s4p\phantom{\rule{4pt}{0ex}}^{6}P_{3/2}$ and ionic $3{d}^{5}\phantom{\rule{4pt}{0ex}}4s{\phantom{\rule{4pt}{0ex}}}^{5}{S}_{2}\ensuremath{\rightarrow}3{d}^{5}\phantom{\rule{4pt}{0ex}}4p{\phantom{\rule{4pt}{0ex}}}^{5}{P}_{3}$ transitions, yielding two sets of isotope shifts. The mass and field shift factors for both transitions have been calculated in the multiconfiguration Dirac-Fock framework and were combined with a King plot analysis in order to obtain a consistent set of mean-square charge radii which, together with earlier work on neutron-deficient Mn, allow the study of nuclear structure changes from $N=25$ across $N=28$ up to $N=39$. A clear development of deformation is observed towards $N=40$, confirming the conclusions of the nuclear moments studies. From a Monte Carlo shell-model study of the shape in the Mn isotopic chain, it is suggested that the observed development of deformation is not only due to an increase in static prolate deformation but also due to shape fluctuations and triaxiality. The changes in mean-square charge radii are well reproduced using the Duflo-Zuker formula except in the case of large deformation.

Laser and decay spectroscopy of the short-lived isotope Fr-214 in the vicinity of the N=126 shell closure

Abstract: G. J. Farooq-Smith,1,2,* T. E. Cocolios,1,2 J. Billowes,1 M. L. Bissell,1,2 I. Budinčević,2 T. Day Goodacre,1,3 R. P. de Groote,2 V. N. Fedosseev,3 K. T. Flanagan,1 S. Franchoo,4 R. F. Garcia Ruiz,1,2 H. Heylen,2 R. Li,4,† K. M. Lynch,2,5 B. A. Marsh,3 G. Neyens,2 R. E. Rossel,3,6 S. Rothe,1,3 H. H. Stroke,7 K. D. A. Wendt,6 S. G. Wilkins,1 and X. F. Yang2 1School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, United Kingdom 2KU Leuven, Instituut voor Kernen Stralingsfysica, B-3001 Leuven, Belgium 3EN Department, CERN, CH-1211 Geneva 23, Switzerland 4Institut de Physique Nucléaire d’Orsay, F-91406 Orsay, France 5ISOLDE, PH Department, CERN, CH-1211 Geneva 23, Switzerland 6Institut für Physik, Johannes Gutenberg-Universität, D-55128 Mainz, Germany 7Department of Physics, New York University, New York, New York 10003, USA (Received 10 August 2016; published 4 November 2016; publisher error corrected 17 November 2016)

High-resolution laser spectroscopy with the Collinear Resonance Ionisation Spectroscopy (CRIS) experiment at CERN-ISOLDE

Abstract: The Collinear Resonance Ionisation Spectroscopy (CRIS) experiment at CERN has achieved high-resolution resonance ionisation laser spectroscopy with a full width at half maximum linewidth of 20(1) MHz for 219 , 221 Fr, and has measured isotopes as short lived as 5 ms with 214 Fr. This development allows for greater precision in the study of hyperfine structures and isotope shifts, as well as a higher selectivity of single-isotope, even single-isomer, beams. These achievements are linked with the development of a new laser laboratory and new data-acquisition systems.

Combined high-resolution laser spectroscopy and nuclear decay spectroscopy for the study of the low-lying states in Fr 206 , At 202 , and Bi 198

Abstract: High-resolution laser spectroscopy was performed on $^{206}\mathrm{Fr}$ with the collinear resonance ionization spectroscopy (CRIS) experiment at CERN-ISOLDE. The hyperfine structure and isotope shift of the ground, first isomeric and second isomeric states were measured. The hyperfine components were unambiguously assigned to each nuclear state by means of laser-assisted nuclear decay spectroscopy. The branching ratios in the $\ensuremath{\alpha}$ decay of $^{206}\mathrm{Fr}$ and $^{202}\mathrm{At}$ were also measured for the first time with isomerically purified beams. The extracted hindrance factors allow determination of the spin of the ground, first isomeric, and second isomeric states in $^{202}\mathrm{At}$ and $^{198}\mathrm{Bi}$.

Versatile Ion-polarized Techniques On-line (VITO) experiment at ISOLDE-CERN

Abstract: The VITO (Versatile Ion-polarized Techniques Online) project is a new experimental setup at the ISOLDE facility at CERN. VITO is a dedicated beam line for producing laser-induced spin-polarized beams of both, atoms and ions, and it has been commissioned in response to the continuously growing demand for the use of spin-polarized beams. The new VITO beam line is a modification of the formerly existing ultra-high vacuum beam line, connecting ASPIC (Apparatus for Surface Physics and Interfaces at CERN), and it has been under construction since the beginning of 2014. Once fully commissioned, VITO will open up numerous possibilities for carrying out multidisciplinary experiments in the areas of nuclear and solid state physics, fundamental interaction physics and biophysics. In its final stage the VITO beam line will provide three fully independent experimental stations: UHV chamber for material science applications, a β-asymmetry station where highly-polarized ions will be available, and a central open-end station suitable for travelling experiments. The VITO beam line will operate in two different modes providing either beams of spin-polarized atoms or ions, or non-polarized ion beams to all three end stations operating from 10 −10 mbar to 50 mbar. Recent experimental campaigns with stable and radioactive beams have allowed for testing VITO’s constituent parts and have demonstrated 96% of ion beam transmission to the collection chamber installed on the central station. The first experimental results obtained with on-line Perturbed Angular Correlation (PAC) spectroscopy using 68m Cu ion-beams will be briefly discussed.

Publisher's Note: Isomer Shift and Magnetic Moment of the Long-Lived 1/2^{+} Isomer in _{30}^{79}Zn_{49}: Signature of Shape Coexistence near ^{78}Ni [Phys. Rev. Lett. 116, 182502 (2016)].

Abstract: This corrects the article DOI: 10.1103/PhysRevLett.116.182502.