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Theses

Isomères peuplés par fragmentation dans les noyaux riches en neutrons de masse A = 180-200

Abstract : The neutron-rich nuclei of the A~180-200 transitional region presents many interests for nuclear physicists. In particular, the best examples of K-isomerism, which can be found in the A~180-200 region, are predicted to occur on the neutron-rich side of the valley of stability and are thus barely populated by standard nuclear reactions. In addition, the gamma-decay studies of K-isomers provide critical information about the evolution of the nuclear structure from prolate to spherical shape in the transitional region. Projectile fragmentation has proven to be an efficient method for populating heavy neutron-rich isotopes with cross-sections sufficient to perform gamma-ray spectroscopy. Thus, the FRagment Separator (FRS) associated with gamma-ray spectroscopy techniques has been successfully used at GSI to search for K-isomers with lifetimes ranging from nano- to milliseconds in the mass region around A~190-200. These isomers were produced following the fragmentation of a 1 GeV/nucleon 208Pb beam impinging on a 1.6 g/cm2 Be target. The fragments were separated by the FRS working in achromatic mode and identified using the Brho-DeltaE-TOF method. Ions were stopped in a 4 mm thick Al catcher covering an implantation area of 3 * 16 cm2. Prompt and delayed gamma-rays in coincidence with implanted ions of interest were measured using a Segmented Clover Ge Array whose efficiency was about 6 % at 1.33 MeV for the central position of the catcher. Establishing a new experimental technique, this thesis focuses on the observation of several new isomers in neutron-rich A=190-200 nuclei providing the first nuclear structure information from successive gamma decay cascades, with special emphasis on 190W and 197Ir new data where K-isomeric states were identified. Moreover, the ability of this novel method to reach high spin states has been demonstrated by populating K=35/2- isomeric state in 175Hf, 179W and 181Re. This state corresponds to the highest spin value ever observed in projectile fragmentation.
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https://tel.archives-ouvertes.fr/tel-00002475
Contributor : Pascale Mayet <>
Submitted on : Tuesday, February 25, 2003 - 5:51:16 PM
Last modification on : Thursday, April 23, 2020 - 2:26:21 PM
Long-term archiving on: : Monday, September 20, 2010 - 12:08:54 PM

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  • HAL Id : tel-00002475, version 2

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Pascale Mayet. Isomères peuplés par fragmentation dans les noyaux riches en neutrons de masse A = 180-200. Physique Nucléaire Théorique [nucl-th]. Université Louis Pasteur - Strasbourg I, 2001. Français. ⟨tel-00002475v2⟩

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