Conférences et séminaires » Séminaire de Andreas GOERGEN
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Shapes and shape coexistence in atomic nuclei.
(DAPNIA/SPhN, CEA Saclay, GIF-sur-YVETTE )
le Mardi 25 juillet 2006 à 16 h00
Salle de Visioconférences - Bâtiment 25
IPHC, 23 rue du Loess, Strasbourg-Cronenbourg
The shape of the nucleus is governed by a delicate interplay of the macroscopic liquid-drop properties of nuclear matter and microscopic shell effects. Under certain conditions the nucleons can occupy different orbitals leading to different nuclear shapes.
Coulomb excitation experiments on neutron-deficient krypton isotopes will be discussed that resulted in the first direct measurement of the shape of a radioactive nucleus in a short-lived excited state. The results confirm the coexistence of elongated (prolate) and compressed (oblate) shapes within a very narrow energy range. The precise experimental knowledge of the electromagnetic moments for several excited states and the transition strengths between them put stringent constraints on modern nuclear structure models.
Atomic nuclei can also change their shape with increasing angular momentum. Rapidly rotating nuclei are predicted to undergo a Jacobi shape transition, which is a purely macroscopic effect, while the occupation of steeply down-sloping intruder orbitals can drive the nucleus to extreme deformation at the highest spins. Experiments searching for such extreme nuclear shapes will be discussed, together with future opportunities with intense radioactive beams (SPIRAL-2) and the next-generation gamma spectrometer AGATA.