Köln 2004 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 16: Nuclear Structure/Spectroscopy II

HK 16.6: Vortrag

Dienstag, 9. März 2004, 17:15–17:30, A

A measure for γ-deformation in heavy nuclei — •C. Scholl, V. Werner, and P. von Brentano — Institut für Kernphysik, Universität zu Köln

A way to measure the γ-deformation of a nucleus is found by analysis of shape invariants. While β and γ are deformation parameters in the geometrical model, they are not always easy to define in all cases, e.g., in vibrational nuclei. The shape invariants K₃ and K₄ are connected to effective β- and γ- deformation parameters by simple formulas. In general, they are given by huge sums over matrix elements. Nevertheless, introducing the Q-phonon scheme and its selection rules, it was shown [1] that a good approximation to K₄ can be given involving only two B(E2) values in the ground state band. Using the same approximation for K₃ one can identify this quantity with the quadrupole moment of the first excited 2⁺ state, but deviations are found to be large within the IBM. In a second approximation an inclusion of the B(E2) strengths of the 2_γ⁺ (in a vibrator the two-phonon 2⁺) state lead to an accuracy of the approximation within a few percent in the IBM. That means fitting a two parameter Hamiltonian to data, the value of K₃^approx corresponds to the value of K₃ with an accuracy of a few percent. K₃ and the corresponding effective γ-deformation parameter are given for a collection of nuclei.

[1] V. Werner et al., Phys. Lett. B 521 (2001) 146. ^∗ supported by the DFG under contract Br799/11-1