Deformation change in light iridium nuclei from laser spectroscopy

D. Verney; L. Cabaret; J. E. Crawford; H. T. Duong; B. Fricke; J. Genevey; G. Huber; F. Ibrahim; M. Krieg; F. Le Blanc; J. K. P. Lee; G. Le Scornet; D. Lunney; J. Obert; J. Oms; J. Pinard; J. C. Puteaux; K. Rashid; B. Roussière; J. Sauvage; V. Sebastian

doi:10.1140/epja/i2006-10140-7

2023 Impact factor 2.6

Hadrons and Nuclei

Eur. Phys. J. A (2006) 30: 489-518
https://doi.org/10.1140/epja/i2006-10140-7

Nuclear Structure and Reactions

Deformation change in light iridium nuclei from laser spectroscopy

D. Verney¹^*, L. Cabaret², J. E. Crawford³, H. T. Duong², B. Fricke⁷, J. Genevey⁴, G. Huber⁵, F. Ibrahim⁴, M. Krieg⁵, F. Le Blanc¹, J. K. P. Lee³, G. Le Scornet⁶, D. Lunney⁶, J. Obert¹, J. Oms¹, J. Pinard², J. C. Puteaux¹, K. Rashid⁷, B. Roussière¹, J. Sauvage¹, V. Sebastian⁵ and the ISOLDE Collaboration

¹ Institut de Physique Nucléaire, IN2P3-CNRS/Université Paris Sud-XI, F-91406, Orsay Cedex, France
² Laboratoire Aimé Cotton, CNRS, F-91405, Orsay Cedex, France
³ Physics Department, McGill University, H3A2T8, Montréal, Canada
⁴ Laboratoire de Physique Subatomique et de Cosmologie, IN2P3-CNRS/Université Joseph Fourier-Grenoble I, F-38026, Grenoble Cedex, France
⁵ Institut für Physik der Universität Mainz, D-55099, Mainz, Germany
⁶ Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, IN2P3-CNRS/Université Paris Sud-XI, F-91405, Orsay Cedex, France
⁷ Institut für Theoretische Physik der Universität Kassel, D-34109, Kassel, Germany
⁸ CERN, CH-1211, Genève 23, Switzerland

^* e-mail: verney@ipno.in2p3.fr

Received: 29 June 2006
Accepted: 27 October 2006
Published online: 29 November 2006

Abstract

Laser spectroscopy measurements have been performed on neutron-deficient and stable Ir isotopes using the COMPLIS experimental setup installed at ISOLDE-CERN. The radioactive Ir atoms were obtained from successive decays of a mass-separated Hg beam deposited onto a carbon substrate after deceleration to 1kV and subsequently laser desorbed. A three-color, two-step resonant scheme was used to selectively ionize the desorbed Ir atoms. The hyperfine structure (HFS) and isotope shift (IS) of the first transition of the ionization path 5d ⁷6s ²⁴ F _9/2 → 5d ⁷6s6p ⁶ F _11/2 at 351.5nm were measured for ^182-189Ir, ¹⁸⁶Ir^m and the stable ^{191, 193}Ir. The nuclear magnetic moments μ_I and the spectroscopic quadrupole moments Q_s were obtained from the HFS spectra and the change of the mean square charge radii from the IS measurements. The sign of μ_I was experimentally determined for the first time for the masses 182≤A≤189 and the isomeric state ¹⁸⁶Ir^m. The spectroscopic quadrupole moments of ¹⁸²Ir and ¹⁸³Ir were measured also for the first time. A large mean square charge radius change between ¹⁸⁷Ir and ¹⁸⁶Ir^g and between ¹⁸⁶Ir^m and ¹⁸⁶Ir^g was observed corresponding to a sudden increase in deformation: from β₂ ≃ + 0.16 for the heavier group A = 193, 191, 189, 187 and 186m to β₂≥ + 0.2 for the lighter group A = 186g, 185, 184, 183 and 182. These results were analyzed in the framework of a microscopic treatment of an axial rotor plus one or two quasiparticle(s). This sudden deformation change is associated with a change in the proton state that describes the odd-nuclei ground state or that participates in the coupling with the neutron in the odd-odd nuclei. This state is identified with the π3/2⁺[402] orbital for the heavier group and with the π1/2^-[541] orbital stemming from the 1h _9/2 spherical subshell for the lighter group. That last state seems to affect strongly the observed values of the nuclear moments.