Relativistic Quasiparticle Random Phase Approximation in axial symmetry

157 Pages·2007·4.14 MB·English

Relativistic Quasiparticle Random
Phase Approximation in Deformed
Nuclei
Dissertation
von
Daniel Pen˜a Arteaga
Institut fu¨r Theoretische Physik T30
Physik Department
Technische Universit¨at Mu¨nchen
Mai 2007
ii
Physik–Department der Technischen Universit¨at Mu¨nchen
Theoretische Physik T30
Relativistic Quasiparticle Random Phase
Approximation in Deformed Nuclei
Daniel Pen˜a Arteaga
Vollst¨andiger Abdruck der von der Fakult¨at fu¨r Physik der Technischen Universit¨at
Mu¨nchen zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften (Dr. rer. nat.)
genehmigten Dissertation.
Vorsitzender: Univ.-Prof. Dr. R. Kru¨cken
Pru¨fer der Dissertation: 1. Univ.-Prof. Dr. P. Ring
2. Univ.-Prof. Dr. W. Weisse
Die Dissertation wurde am 16.05.2007 bei der Technischen Universit¨at Mu¨nchen ein-
gereicht und durch die Fakult¨at fu¨r Physik am 25.06.2007 angenommen.
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Abstract
Covariant density functional theory is used to analyse the response to the E1 and M1
electromagnetic transition operators in superfluid deformed nuclei in the framework of
self-consistent Hartree-Bogoliubov theory and relativistic quasiparticle random phase
(RQRPA) approximation. The fully self-consistent RHB+RQRPA equations are posed
for the case of axial symmetry and for three different kinds of energy functionals, and
solvedwiththehelpofanewparallelcode. Specialcareistakeninordertovalidatethe
proper decoupling of spurious modes. Results of the first multipole magnetic operator
(M1) response in light and heavy deformed nuclei are presented and analysed; in par-
ticular, the scissors mode and spin excitations. Qualitative agreement with experiment
is obtained for the position of the scissors mode, and its structure as a rotation of the
deformed neutron density against the deformed proton density reproduced. In addition
to the scissors mode, a soft M1 mode with strong orbital character is found in heavy
nucleiatrelativelylowenergies. Fromtheanalysisoftheprotonandneutrontransition
densities in the intrinsic frame, and from the structure of the RQRPA amplitudes, it is
concluded that this mode corresponds to a collective rotation of the deformed neutron
skin against the deformed proton-neutron core. The response in light and heavy nuclei
to the electric dipole operator (E1) is also given consideration. The position of the
Giant Dipole Resonance is well reproduced within the RHB+RQRPA framework in
axial symmetry. The effects of superfluidity and deformation on the Pygmy Dipole
Resonance are closely examined. Excellent agreement with recent experimental results
is found.
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Acknowledgements
First and foremost I would like to thank my supervisor, Prof. Dr. Peter Ring, not
only for stimulating discussions and timely advice, but also for his support throughout
the various phases of the work presented in this document. His understanding and
experience in many areas has made a pleasure working with him. I am particularly
grateful for his optimism and overall confidence in the project, always trying to point
me on the right direction but giving me enough leeway to learn from my own mistakes.
Many thanks go to Roger Hilton, who was always a source of good humour and inter-
estingconversationswhileattheTUM.Hepatientlyreadthefirstdraftsandhelpedme
polish all the rough edges, both in the contents and in the use of the English language.
It is a pleasure for me to thank all my colleagues at the TUM Theory Department
and at the TUM campus in Garching, who have provided support and company during
my time in Munich, with a special mention to Nils Paar, Christian Rummel, Ioannis
Daoutidis, Andreas Serr, Marco Ajello, Rasmus Voss, Alfredo Alexander-Katz, Elena
Litvinova, Marta Balb´as, Javier Madron˜ero, and all the guests that contributed to
make me feel at home at the University.
Many friends have helped me to persevere in my efforts, sharing with me their free
time, good will and beer from all around the world. Even though they are too many
to mention all, they know who they are. Thanks to all!
And finally, my family deserves a very special thanks, the best I can give. Mam´a, Pap´a,
T´ıo, Lola, Gabi, Carmelita, Lolo, ..., esta t´esis est´a dedicada, con mucho carin˜o, a
todos vosotros.
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“Writing in English is the most ingenious torture ever
devised for sins committed in previous lives.”
— Jame Joyce, 1882-1941
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