Investigation of the photon strength function in ¹²⁸Te using the (γ, γ^'γ'') reaction

In most nucleosynthesis calculations the concept of photon strength functions (PSF) is used within the statistical model to describe the average EM decay properties of excited nuclei. The basis of this approach is the validity of the Brink-Axel hypothesis. The PSF's are assumed to be independent of the excitation energy and the specific properties of the involved excited states. Model-independent experimental data on the proof of this concept is still scarce. The new experimental technique of combining real photon scattering and coincidence γ-ray spectroscopy at the γ³ setup at HIγS allows to investigate the decay pattern of photo-excited states in great detail. Results on ¹²⁸Te are presented, which show a clear discrepancy to the statistical model assumption of a constant PSF and thus disagrees with the Brink-Axel hypothesis for the presented case.