Modern Photon Scattering and Photoactivation Experiments in Nuclear - and Astrophysics

The experimental progress achieved in the last years enables nowadays photon scattering and photoactivation experiments of considerably increased sensitivities opening new fields of application. In this report results are summarized from recent experiments performed at the well-established bremsstrahlung facilities of the 4.3 MV Stuttgart DYNAMITRON accelerator. Three current topics will be discussed in more detail: The systematics of E1 two-phonon excitations of the type (2⁺ ⊗ 3^-) in nuclei near shell closures; the first observation of a population inversion of nuclear states, the precondition for a possible γ-ray laser, by feeding from higher-lying photo-excited states (NRF experiments on ¹⁰³Rh); and the depopulation of the quasistable isomer in ¹⁸⁰Ta by resonant photoabsorption. The consequences for the puzzling nucleosynthesis of nature's rarest isotope ¹⁸⁰Ta are discussed.