M. Schumann

The new photoactivation facility at the 4.3 MV Stuttgart DYNAMITRON: setup, performance, and first applications

At the Stuttgart 4: 3M V DYNAMITRON accelerator a newbremsstrahlung irradiation facility w as installed for photoactivation experiments to complement the well-established arrangement for systematic photon-scattering studies taking advantage of the high photon fluxes achievable at this high-current accelerator. The population or depopulation of isomeric states in low-energy photon-induced reactions ðEg ¼ 0:5–4:0 MeV) can be studied with sensitivities far beyond previous limits. The setup of this facility, its performance, and the absolute calibrations are described in detail. First exemplary results for a test case, the reaction 115 In ðg;g 0 Þ 115m In, are presented and analyzed in combination with data from low-energy photon-scattering experiments ( 115 In ðg;g 0 Þ 115 In). The quality of the results demonstrates the

Photoactivation of 180Tam: Does it affect s-process nucleosynthesis of nature’s rarest stable isotope?

The depopulation of the quasistable isomer (Jπ=9−, Ex=75 keV) in 180Ta through resonant photoabsorption was studied with intense bremsstrahlung. The results show evidence for a deexciting level with an energy of 1.085 MeV or below, leading to a dramatic acceleration of the isomer decay to the short-lived Jπ=1+ ground state under stellar s-process conditions. Consequences for a possible nucleosynthesis of nature’s rarest isotope 180Ta within the s process are discussed.

Photoactivation of 180MTa at Astrophysically Relevant Energies

A possible connection of the isomeric state in 180Ta to its ground state band via low-lying intermediate states (IS) was investigated by means of photoactivation using bremsstrahlung. A depopulation of the isomer has been found down to a bremsstrahlung endpoint-energy of 1 MeV but not at the lowest bombarding energy of 0.8 MeV. Therefore an IS slightly lower than 1 MeV has to be assumed. Further IS were observed at about 1.2, 1.5, 2.1, 2.5, and 2.8 MeV, respectively.