Coulomb excitation of pear-shaped nuclei

¹ Oliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE, UK
² CERN, CH-1211 Geneva 23, Switzerland
³ School of Computing, Engineering and Physical Sciences, University of the West of Scotland, Glasgow, PA1 2BE UK
⁴ Department of Physics & Astronomy, University of the Western Cape, Private Bag X17, Bellville, 7535 South Africa
⁵ TRIUMF, Vancouver, V6T 2A3 BC, Canada
⁶ Physics Department, Lund University, Box 118 Lund, SE-221 00, Sweden
⁷ Department of Physics, University of Michigan, Ann Arbor, 48104 MI, USA
⁸ INFN Laboratori Nazionali di Legnaro, Legnaro, 35020 PD, Italy
⁹ Instituut voor Kern- en Stralingsfysica, KU Leuven, Leuven, B-3001, Belgium
¹⁰ Department of Physics, University of Guelph, Guelph, N1G 2W1 Ontario, Canada
¹¹ Institute for Nuclear Physics, University of Cologne, Cologne, 50937 Germany
¹² Institut für Kernphysik, Technische Universität Darmstadt, Darmstadt, 64289 Germany
¹³ Heavy Ion Laboratory, University of Warsaw, Warsaw, PL-02-093 Poland
¹⁴ Department of Physics, University of Jyvaskyla, P.O. Box 35, Jyvaskyla, FIN-40014 Finland
¹⁵ Helsinki Institute of Physics, P.O. Box 64, Helsinki, FIN-00014 Finland
¹⁶ Department of Physics, University of Oslo, P.O.Box 1048, Oslo, N-0316 Norway
¹⁷ Department of Physics, University of York, York, YO10 5DD UK
¹⁸ JINR Dubna, Dubna, Moscow Region 141980, Russia
¹⁹ Consejo Superior De Investigaciones Científicas, Madrid, S 28040 Spain
²⁰ IRFU CEA, Université Paris-Saclay, Gif-sur-Yvette, F-91191 France

^* Corresponding author: peter.butler@liverpool.ac.uk

Published online: 4 December 2019

Abstract

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 have observed the low-lying quantum states in ²²⁴Rn and ²²⁶Rn 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.