Photoactivation and photon-scattering experiments of astrophysical relevance

Abstract

The availability of high-flux, continuous-energy DC bremsstrahlung photon beams and the progress in modern X-ray and γ-spectroscopy have led to a real revival of both the photon scattering (Nuclear Resonance Fluorescence (NRF)) and the photoactivation techniques and enabled experiments with sensitivities far beyond previous limits. A new bremsstrahlung irradiation facility for photoactivation experiments was installed at the Stuttgart 4.3 MV Dynamitron accelerator which complements the well-established photon scattering facility. Exemplary results for a test reaction, the photoactivation of the most investigated isomer 115 m In, in combination with data from low-energy photon-scattering experiments ( 115In(γ,γ′) 115In), demonstrate the capability of this new installation. As a first application the depopulation of the famous 180 m Ta-isomer by photoactivation was studied in detail using the world's stock of enriched 180Ta material. A joint Darmstadt-Karlsruhe-München-Stuttgart-Youngstown - collaboration succeeded in observing the depopulation of the isomer down to excitation energies of ≈ 1 MeV. The astrophysical implications of these results, the consequences for the puzzling nucleosynthesis of nature's rarest naturally occurring isotope, 180Ta, are discussed. Future perspectives of the photoactivation technique and their application in nuclear astrophysics are outlined.