The Two-Photon Decay of the 11-/2 Isomer of 137Ba and Mixed-Symmetry States of 92,94Zr and 94Mo

1. Front Matter

   Pages i-xv

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2. Introduction

   • Christopher Walz

   Pages 1-8

3. Theoretical Background of the Two-Photon Decay Experiment

   • Christopher Walz

   Pages 9-17

4. Experimental Setup of the Two-Photon Decay Experiment

   • Christopher Walz

   Pages 19-28

5. Data Analysis and Results of the Two-Photon Decay Experiment

   • Christopher Walz

   Pages 29-43

6. Theoretical Background of the Proton Scattering Experiments

   • Christopher Walz

   Pages 45-62

7. The Experimental Setup at iThemba LABS

   • Christopher Walz

   Pages 63-70

8. Data Analysis and Results of the Proton Scattering Experiments

   • Christopher Walz

   Pages 71-105

9. Interpretation

   • Christopher Walz

   Pages 107-143

10. Summary and Outlook

    • Christopher Walz

    Pages 145-148

11. Back Matter

    Pages 149-160

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This work focuses on new electromagnetic decay mode in nuclear physics. The first part of the thesis presents the observation of the two-photon decay for a transition where the one-photon decay is allowed. In the second part, so called quadrupole mixed-symmetry is investigated in inelastic proton scattering experiments. In 1930 Nobel-prize winner M. Goeppert-Mayer was the first to discuss the two-photon decay of an exited state in her doctoral thesis. This process has been observed many times in atomic physics. However in nuclear physics data is sparse. Here this decay mode has only been observed for the special case of a transition between nuclear states with spin and parity quantum number 0+. For such a transition, the one-photon decay – the main experimental obstacle to observe the two-photon decay – is forbidden. Furthermore, the energy sharing and angular distributions were measured, allowing conclusions to be drawn about the multipoles contributing to the two-photon transition. Quadrupole mixed-symmetry states are an excitation mode in spherical nuclei which are sensitive to the strength of the quadrupole residual interaction. A new signature for these interesting states is presented which allows identification of mixed-symmetry states independently of electromagnetic transition strengths. Furthermore this signature represents a valuable additional observable to test model predictions for mixed-symmetry states.

• Double-gamma decay
• Electromagnetic nuclear decay mode
• Hexadecapole mixed-symmetry states
• Mixed-symmetry states in spherical nuclei
• Origin of collectivity in spherical nuclei
• Second order electromagnetic decay
• Signatures of mixed-symmetry states
• Two-photon decay

• -, -, Wiesbaden, Germany

  Christopher Walz

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