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The two-photon decay of the 11/2- isomer of 137Ba and mixed-symmetry states of 92,94Zr and 94Mo

Walz, Christopher (2014):
The two-photon decay of the 11/2- isomer of 137Ba and mixed-symmetry states of 92,94Zr and 94Mo.
Darmstadt, Christopher Walz, TU Darmstadt, [Online-Edition: http://tuprints.ulb.tu-darmstadt.de/4056],
[Ph.D. Thesis]

Abstract

The first part of this thesis covers the two-photon decay of the 11/2- isomer in 137Ba. Clear evidence of this exotic decay mode is found, which opens up the possibility to use the two-photon decay probability as a general tool to investigate the structure of atomic nuclei. Details on the experiment are given, and the major challenges to successfully perform this difficult experiment are outlined. The two-photon decay experiment was conducted with the new LaBr3-detector ball which was setup from scratch in the framework of this thesis. The properties and performance of this powerful detector system - consisting of 18 large LaBr3-detectors - are discussed.

Furthermore, proton scattering at 200 MeV has been performed on the nuclei 92,94Zr, 94,96Mo and 70Zn.The measured cross sections are compared to calculations in the framework of the Quasi-Particle Phonon Model (QPM). Conclusions about the validity of the QPM results are drawn. A comparison of the excitation cross sections of the 2+1 states and the one-phonon quadrupole states with mixed neutron and proton symmetry (2+ms) allows to prove the special character of the 2+ms states independently of electromagnetic transition strengths. The possible existence of 3- and 4+ states with mixed proton and neutron symmetry is discussed. Furthermore the origin of collectivity of low-lying states in spherical nuclei is investigated in the QPM.

Item Type: Ph.D. Thesis
Erschienen: 2014
Creators: Walz, Christopher
Title: The two-photon decay of the 11/2- isomer of 137Ba and mixed-symmetry states of 92,94Zr and 94Mo
Language: English
Abstract:

The first part of this thesis covers the two-photon decay of the 11/2- isomer in 137Ba. Clear evidence of this exotic decay mode is found, which opens up the possibility to use the two-photon decay probability as a general tool to investigate the structure of atomic nuclei. Details on the experiment are given, and the major challenges to successfully perform this difficult experiment are outlined. The two-photon decay experiment was conducted with the new LaBr3-detector ball which was setup from scratch in the framework of this thesis. The properties and performance of this powerful detector system - consisting of 18 large LaBr3-detectors - are discussed.

Furthermore, proton scattering at 200 MeV has been performed on the nuclei 92,94Zr, 94,96Mo and 70Zn.The measured cross sections are compared to calculations in the framework of the Quasi-Particle Phonon Model (QPM). Conclusions about the validity of the QPM results are drawn. A comparison of the excitation cross sections of the 2+1 states and the one-phonon quadrupole states with mixed neutron and proton symmetry (2+ms) allows to prove the special character of the 2+ms states independently of electromagnetic transition strengths. The possible existence of 3- and 4+ states with mixed proton and neutron symmetry is discussed. Furthermore the origin of collectivity of low-lying states in spherical nuclei is investigated in the QPM.

Place of Publication: Darmstadt
Publisher: Christopher Walz
Uncontrolled Keywords: two-photon decay, LaBr3-detectors, mixed-symmetry states, proton scattering,
Divisions: 05 Department of Physics > Institute of Nuclear Physics
05 Department of Physics
Date Deposited: 20 Jul 2014 19:55
Official URL: http://tuprints.ulb.tu-darmstadt.de/4056
URN: urn:nbn:de:tuda-tuprints-40566
Referees: Pietralla, Prof. Dr. Norbert and Scheit, Dr. Heiko
Refereed / Verteidigung / mdl. Prüfung: 9 July 2014
Alternative keywords:
Alternative keywordsLanguage
Zwei-Photonenzerfall, LaBr3-Detektoren, gemischt-symmetrische Zustände, ProtonenstreuungGerman
Alternative Abstract:
Alternative abstract Language
Der erste Teil dieser Dissertation behandelt den Zwei-Photonenzerfall des 11/2- Isomers in 137Ba. Ein Nachweis dieser exotische Zerfallsmode ist gelungen. Dies ermöglicht es, den Zwei-Photonenzerfall als neue Methode zur Untersuchung spezieller Akspekte der Struktur von Atomkernen zu verwenden. Das Experiment ist im Detail beschrieben und die Hauptschwierigkeit für eine erfolgreiche Durchführung eines Zwei-Photonenzerfalls Experiments werden diskutiert. Im Rahmen dieser Arbeit wurde ein neuer LaBr3-Detektorball aufgebaut. Die Eigenschaften und die Performance dieses Detektorsystems - bestehend aus 18 großen LaBr3-Detektoren - werden präsentiert. Die Kerne 92,94Zr, 94,96Mo und 70Zn wurden in einem Protonenstreuexperiment bei einer Energie von 200 MeV untersucht. Die gemessenen Anregungs-Wirkungsquerschnitte wurden mit Modellrechnungen im Rahmen des Quasi-Particle Phonon Model (QPM) verglichen und Rückschlüsse über die Gültigkeit des QPMs konnten gezogen werden. Ein Vergleich der Wirkungsquerschnitte der 2+1 Zustände mit denen von Zuständen mit gemischter Neutronen- und Protonensymmetrie (2+ms), erlauben den gemischt-symmetrischen Charakter der 2+ms Zustände zu beweisen, unabhängig von elektromagnetischen Übergangsstärken. Des Weiteren wird die mögliche Existenz von 3- und 4+ Zuständen mit gemischter Protonen- und Neutronensymmetrie diskutiert. Zusätzlich bietet das QPM Einblicke in die Entstehung von niederenergetischen, kollektiven Zuständen in sphärischen Kernen.German
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