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

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### Contents

1 | |

9 | |

3 Experimental Setup of the TwoPhoton Decay Experiment | 19 |

4 Data Analysis and Results of the TwoPhoton Decay Experiment | 29 |

5 Theoretical Background of the Proton Scattering Experiments | 45 |

6 The Experimental Setup at iThemba LABS | 63 |

7 Data Analysis and Results of the Proton Scattering Experiments | 71 |

8 Interpretation | 107 |

9 Summary and Outlook | 145 |

Appendix A
Racah Algebra | 149 |

Appendix B
Results of the ProtonScattering Experiments | 150 |

### Other editions - View all

The Two-Photon Decay of the 11-/2 Isomer of 137ba and Mixed-Symmetry States ... CHRISTOPHER. WALZ No preview available - 2018 |

The Two-Photon Decay of the 11-/2 Isomer of 137Ba and Mixed-Symmetry States ... Christopher Walz No preview available - 2016 |

### Common terms and phrases

2+1 RPA 2qp-states amplitudes angle of 72 angular distribution background boson branching ratio Compton scattering contributions data point detector pairs determined dipole electron scattering energy condition energy gate energy resolution excited focal plane g-factors Gaussian function GEANT4 hamiltonian hexadecapole iThemba LaBr3-detectors left-hand side lookup table low-lying M1-transition magnetic matter transition measured mixed-symmetry mixing momentum neutron transition Nucl nuclear structure nuclear structure model nuclei nucleon octupole one-phonon one-photon decay particle peak phonon Phys plastic scintillators proton and neutron proton scattering cross proton-neutron QRPA QRPA-phonons quantum numbers quasiparticle radioactive random coincidences residual interaction right-hand side scattering angles scattering cross sections Sect sequential shown single-particle spectra spectrometer spin and parity Springer sum energy spectrum symmetry target theoretical thesis transition densities transition matrix transition matrix elements transition radii transition strengths two-photon decay experiment two-photon decay probability Walz wave functions wire chamber