Spektroskopie der Oktupolkorrelationen von 231Pa und 229Pa mit adaptierten Koinzidenzteilchendetektorsystemen

The shape of a nucleus can be defined in a classical view by a sphere of constant density of positive space-charge in a body-fixed frame of reference. Experimental observations can be interpreted as deviations from spherical symmetry of the nucleus. Static shapes of nuclei in the periodic table near the valley of stability predominantly are rotationally symmetric and mostly quadrupole deformed (American football or lens). For nuclei in time-dependent excited states asymmetric terms are known, like octupole deformation (pear shape). The group of actinides lies in a transition region with possible "static octupole deformation". For a fixed proton number (Z = 91) the impact of changing octupole correlations with neutron number on the configuration of 31Pa and 229Pa was analysed in the present work. A detector optimized for the reaction 231Pa(22 MeV p,t)229Pa at the Munich Universities tandem accelerator laboratory gave experimental clues of the 229Pa ground-state energy. A detailed study of231Pa by Coulomb-excitation with 148 MeV 32S und 255, 260, 261 MeV 58Ni projectiles can answer open questions on octupole correlations and determines a multitude of transition matrix elements as well as their global parameters in an enlarged level scheme. A segmented coincidence detector for backscattered particles with read-out electronics and software for high resolution, combined with Compton-suppressed and background-reduced-gamma spectroscopy following Coulomb-excitation was developed for the NORDBALL gamma-spectrometer of the Niels Bohr Institute Tandem Accelerator Laboratory, Risø (Denmark). An optional extension of the detector system, built by the University of Warsaw (Poland), can be integrated. For some experiments a Si-detector of the College of Industrial Technology Amagasaki (Japan) was used. The 1/2[530] ground-state band 231Pa could be followed up to spin 39/2-, the 1/2[400]+1/2[660] parity-partner band up to 23/2+ and the 3/2[651] side band up to 37/2+. The simulation of Coulomb-excitation with the code GOSIA helped to fit the parameters of a model system consisting of three bands with 47 levels and interconnecting 672 matrix elements of E1, E2, E3, E4 and M1 transitions to experimental data within chi^2/n=1. As far as possible the calculation remained model-independent and led to values for model parameters of multipole moments and deformation. The determination of signs of matrix elements is discussed. Different methods of error analysis were used. The results were related to the experimental known properties of neighbouring nuclei. A comparison of the results with calculations by the Charles University, Prague (Czech Republic) in the one-quasiparticle-plus-phonon model with Coriolis-coupling is given.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Ludwig-Maximilians-Universität

Year

2003

Author dc:creator

• Würkner, Michael

Contributors dc:contributor

• Boer, Jorrit de

Repository record source_url

https://edoc.ub.uni-muenchen.de/1148/

OAI identifier oai:identifier

oai:edoc.ub.uni-muenchen.de:1148