Tübingen 2003 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 41: Physik mit schweren Ionen IV
HK 41.6: Vortrag
Donnerstag, 20. März 2003, 15:00–15:15, E
Structural effects in the isotopic distributions of the residues of highly excited systems — •Paolo Napolitani1,2, M. V. Ricciardi 1, A. V. Ignatyuk 3, F. Rejmund 2, K. -H. Schmidt 1, and L. Tassan-Got2 — 1GSI, Planckstr. 1, 64291 Darmstadt, Germany — 2IPN, 91406 Orsay, France — 3IPPE, Bondarenko Squ. 1, 249020 Obninsk, Russia
The fine structure effects manifested in processes at low excitation energy, like low energy fission, are well explained by pairing-correlations and shell structure, and are expected to disappear with the increase of the excitation. Recently, several measurements of the production-cross-section for fragmentation at relativistic energies revealed the appearance of even-odd effects in the cross-section distribution for chains of isotopes with given N-Z. The staggering is strongly enhanced for the chain N=Z, it reduces for other even-A nuclei, and it reverses for the most neutron-rich odd-A residues. These phenomena, observed in the residues of rather violent reactions, are related to structural effects in the level-densities below the particle-emission threshold. They are indications for complex effects like mean-field contributions to pairing and alpha clustering. The information on the yields of fragmentation residues provided by the FRS is a precious experimental base for the theoretical study of fine-structure effects in excited nuclei.