1 Introduction and Motivation .................................. 1
2 Nuclear Resonance Fluorescence Experiments ................... 5
2.1 Theoretical background .................................. 5
2.1.1 General idea ..................................... 5
2.1.2 Strength functions ............................... 7
2.1.3 Pygmy resonance ................................. 11
2.1.4 Level densities ................................. 12
2.1.5 Nuclear deformation ............................. 16
2.2 Experimental facilities ................................ 19
2.2.1 Target material ................................. 19
2.2.2 ELBE ............................................ 21
2.2.3 HPγS ............................................ 24
2.3 Calculation of the photo-absorption cross section ...... 26
3 Data Analysis ............................................... 29
3.1 Energy calibration ..................................... 29
3.2 Detector resolution .................................... 30
3.3 Natural and target container background ................ 32
3.4 Compton suppression of the HpGe detectors .............. 37
3.5 Detector response ...................................... 38
3.5.1 Methods of unfolding ............................ 39
3.5.2 BGO veto - yes or no? ........................... 42
3.5.3 1-keV vs 10-keV binning ......................... 46
3.6 Efficiency correction .................................. 48
3.7 Photon flux ............................................ 51
3.7.1 Shape of the photon flux ........................ 52
3.7.2 Absolute height of the photon flux .............. 53
3.8 Atomic background ...................................... 54
3.9 Inelastic scattering and branching ..................... 56
3.10 Discussion of uncertainties ............................ 59
3.11 Data analysis at HIγS .................................. 61
4 Results and Discussion ...................................... 67
4.1 Photo-absorption cross section at ELBE ................. 67
4.2 QRPA calculations ...................................... 68
4.3 The effect of neutron excess ........................... 69
4.4 The effect of nuclear deformation ...................... 72
4.5 Neutron excess versus nuclear deformation .............. 72
4.6 Magnetic dipole contribution to σγ ..................... 74
5 Outlook ..................................................... 77
A Appendix .................................................... 81
A.l Connection of B(E2) and deformation β2 ................. 81
A.2 γDEX2.0 ................................................ 82
A.3 Overview on the Xenon targets and steel containers ..... 86
A.4 11B reference isotope .................................. 87
A.5 56Fe reference isotope ................................. 87
A.6 First excited states of 124,128,132,134Xe ................. 88
A.7 Parameters of RIPL3 for 124,128,132,134Xe ................. 89
A.8 Photo-absorption cross section of 124,128,132,134Xe ....... 90
Literature ..................................................... 92
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