ARENBERG DOCTORAL SCHOOL Faculty of Science Nuclear structure studies of rare francium isotopes using Collinear Resonance Ionization Spectroscopy (CRIS) CERN-THESIS-2015-236 01/09/2015 Ivan Budinceviˇ c´ Supervisor: Dissertation presented in partial Prof. dr. G. Neyens fulfillment of the requirements for the degree of Doctor in Science September 2015 Nuclear structure studies of rare francium isotopes using Collinear Resonance Ionization Spectroscopy (CRIS) Ivan BUDINČEVIĆ Examination committee: Dissertation presented in partial Prof. dr. M. Huyse, chair fulfillment of the requirements for Prof. dr. G. Neyens, supervisor the degree of Doctor Prof. dr. P. Van Duppen in Science Prof. dr. R. Raabe Prof. dr. N. Severijns Prof. dr. E. Janssens dr. K. Flanagan (The University of Manchester, Manchester, United Kingdom) September 2015 © 2015 KU Leuven – Faculty of Science Uitgegeven in eigen beheer, Ivan Budinčević, Celestijnenlaan 200D box 2418, 3001 Leuven (Belgium) Alle rechten voorbehouden. Niets uit deze uitgave mag worden vermenigvuldigd en/of openbaar gemaakt worden door middel van druk, fotokopie, microfilm, elektronisch of op welke andere wijze ook zonder voorafgaande schriftelijke toestemming van de uitgever. All rights reserved. No part of the publication may be reproduced in any form by print, photoprint, microfilm, electronic or any other means without written permission from the publisher. Acknowledgements "I’m bored" is a useless thing to say. You live in a great, big, vast world that you’ve seen none percent of. Louis C.K. This thesis marks the end of an important chapter in my life, a chapter filled with many exciting adventures and discoveries, but also many challenges. I am proud to have been able to contribute to the advancement of human knowledge, however humble the contribution may have been. However, I would have by no means been able to finish this journey without the help of many wonderful people, whom I am very happy to be able to thank here. First and foremost, I would like to thank my supervisor Gerda Neyens, for giving me the opportunity to come to Leuven and to experience being a scientist at CERN. I have learned many things and had unforgettable experiences, all for which I am very grateful. Secondly, I would like to thank the members of my Examination Committee: Mark Huyse, Piet Van Duppen, Riccardo Raabe, Nathal Severijns, Ewald Janssens and Kieran Flanagan. Thank you very much for your helpful comments and our interesting discussions concerning the thesis. I am very grateful to have had such wonderful colleagues from the Nuclear Moments group: Jasna, Wouter, Hanne, Ronald, Ruben, Xiaofei, Stijn, Matthias and Sarina. Thank you for all the things I have learned during "Cultural Fridays", all the times you have helped me when I got stuck with theory, all the laughs we had and so much more. I will also always be indebted to everyone from the CRIS team: Kieran, Jon, Kara, Thomas, Tom, Ilya, Mark, Shane, Greg, thank you all for being a very fun but also very efficient team, and helping me manage my way around i ii ACKNOWLEDGEMENTS the CRIS beamline. I wish you countless more successful experiments, but I do hope they are not all on francium. For the other members of the ISOLDE family: Frank, Vladimir, Bruce, Sebastien, Ralph, Tom, Laura, Stephan, Martin, Tomica, Magda and many others, thank you all for letting me borrow your tools and for being great neighbors. I am very grateful to everyone from the secretariat: Isabelle, Fabienne, Sally and Danielle, to Luc and Bert for fun talks and their IT support, to Willy, Dries, Bart and everyone from the mechanical and electronics workshops for all of their hard work. Luckily my four years at Leuven were not limited to just working, and I am very grateful for having wonderful colleagues who were not related to my field but with whom I had many interesting discussions over our Alma lunches, coffee breaks and beers in the Oude Markt. Hiwa, Gergely, Tomas, Camillo, Daniel, Manisha, Vera, Johana, Riccardo, Freddy, Sara, Deyan and everyone, thank you for all the fun conversations we had. As for everyone outside of IKS, the volleyball gang, my Japanese class buddies, everyone from Dutch class, kung fu and salsa, all of my friends from Serbia, thank you for the countless fun times. To my loving parents, thank you for all of your support throughout my entire life and for giving me so many opportunities. I will be forever grateful. Finally, thank you Maro for all the fun things you have shown me, thank you Mali for always wanting to play with me and for visiting me in Leuven and in CERN and for always being my wonderful little brother, and thank you Tatjana, thank you for all of your support throughout my PhD and for all of the awesome adventures we had. Thank you all. Ivan September 2015, Leuven Preface The goal of this PhD work was to study the structure of exotic francium isotopes by measuring their magnetic dipole and electric quadrupole moments as well as changes in mean-square charge radii, using the newly developed technique of Collinear Resonance Ionization Spectroscopy (CRIS). The first experimental campaigns yielding hyperfine structure and alpha decay results for the francium isotopes 202−206Fr and 218m,219,229,231Fr were performed in August and October 2012 at ISOLDE, CERN. These experiments used the low-resolution pulsed lasers from the RILIS group at ISOLDE, resulting in highly-sensitive background-free measurements, with a linewidth of 1.50(5) GHz. That was sufficient to deduce charge radii and magnetic moments of isomers and ground states, but not sufficient to resolve hyperfine components from isomers and ground states nor to determine quadrupole moments. Four articles were published as a result of this work. The first article by Cocolios et al. [1] gives a description of the CRIS experimental setup. The second article by Flanagan et al. [2] reports on the novelty and sensitivity of the CRIS technique and its application to the study of neutron-deficient francium isotopes and isomers down to 202Fr. The third article by Lynch et al. [3] was the subject of the PhD thesis of Kara Lynch (University of Manchester) who focussed on the analysis and interpretation of the neutron-deficient francium isotopes using decay-assisted collinear resonance ionisation spectroscopy [4]. The fourth article by Budinčević et al. [5] is the core article of this PhD thesis and it is added in the discussion section. It focuses on the study of the neutron-rich francium isotopes in a region of reflection asymmetry. The measurement of the magnetic dipole moments provided insights into the orbital occupations of the valence protons in 219,229,231Fr and supported the tentative spin assignments in 229,231Fr, while the changes in mean-square charge radii provided additional support for the transitional character of 220Fr, having weak octupole correlations, and showed that 228Fr lies outside of the region where such octupole correlations cause reflection-asymmetric nuclear deformations. iii iv PREFACE During the ISOLDE long shutdown period, an upgrade to the CRIS off-line stable ion source was performed as part of this PhD work, enabling tests of a pulsed CW (continuous wave) laser system leading to high-resolution studies on francium isotopes in November 2014. Thanks to the improvement in resolution by nearly 2 orders of magnitude, the spectroscopic quadrupole moment of 219Fr could be measured, which confirmed that the motion of the odd proton in this nucleus is decoupled from the core deformation. This was previously suggested from decay spectroscopy studies. A thorough description of the laser system technical developments, which forms the subject of the PhD thesis by Ruben de Groote, has been described in the paper by de Groote, Budinčević et al.[6], along with a short discussion on the evolution of the structure in the odd neutron-rich francium isotopes. This paper is given in the Appendix of this thesis, while a more extended discussion about shapes and deformation in the francium isotopes is given in the Discussion chapter. In summary, the following papers resulted from the experiments that were carried out as part of my PhD thesis: 1. The Collinear Resonance Ionization Spectroscopy (CRIS) experimental setup at CERN-ISOLDE T.E. Cocolios, H.H. Al Suradi, J. Billowes, I. Budinčević, R.P. de Groote, S. De Schepper, V.N. Fedosseev, K.T. Flanagan, S. Franchoo, R.F. Garcia Ruiz, H. Heylen, F. Le Blanc, K.M. Lynch, B.A. Marsh, P.J.R. Mason, G. Neyens, J. Papuga, T.J. Procter, M.M. Rajabali, R.E. Rossel, S. Rothe, G.S. Simpson, A.J. Smith, I. Strashnov, H.H. Stroke, D. Verney, P.M. Walker, K.D.A Wendt and R.T. Wood Nuclear Instruments and Methods in Physics Research B 317, 565-569 (2013) 2. Collinear Resonance Ionization Spectroscopy of Neutron- Deficient Francium Isotopes K.T. Flanagan, K.M. Lynch, J. Billowes, M.L. Bissell, I. Budinčević, T.E. Cocolios, R.P. de Groote, S. De Schepper, V.N. Fedosseev, S. Franchoo, S. R.F. Garcia Ruiz, H. Heylen, B.A. Marsh, G. Neyens, T.J. Procter, R.E. Rossel, S. Rothe, I. Strashnov, H.H. Stroke, and K.D.A Wendt Physical Review Letters 111, 212501 (2013) 3. Decay-Assisted Laser Spectroscopy of Neutron-Deficient Fran- cium K.M. Lynch, J. Billowes, M.L. Bissell, I. Budinčević, T.E. Cocolios, R.P. de Groote, S. De Schepper, V.N. Fedosseev, K.T. Flanagan, S. Franchoo, R.F. Garcia Ruiz, H. Heylen, B.A. Marsh, G. Neyens, T.J. Procter, R.E. Rossel, S. Rothe, I. Strashnov, H.H. Stroke, and K.D.A Wendt Physical Review X 4, 011055 (2014) PREFACE v 4.