•F. Stedile¹, S. Walter¹, P. von Brentano², J.J. Carroll³, C. Fransen², G. Friessner², H. von Garrel¹, N. Hollmann², J. Jolie², F. Käppeler⁴, O. Karg⁵, U. Kneissl¹, C. Kohstall¹, A. Linnemann², D. Mücher², P. von Neumann-Cosel⁵, N. Pietralla², H.H. Pitz¹, I. Pysmenetska⁵, M. Scheck¹, V. Werner² und K. Wisshak^4
1Inst. f. Strahlenphysik, Univ. Stuttgart
²Inst. f. Kernphysik, Univ. zu Köln
³Dep. of Physics and Astronomy, Youngstown State Univ., Ohio
⁴Inst. f. Kernphysik, FZ-Karlsruhe
⁵Inst. f. Kernphysik, TU Darmstadt

The odd-odd nucleus ¹⁷⁶Lu has a long half-life of about 40 Gyr and is shielded against an r-process synthesis. Its use as s-process chronometer or thermometer critically depends on the possible photoactivation of the low-lying, short-lived, isomeric state (E^*=123 keV; t_1/2=3.635 h) in ¹⁷⁶Lu and its subsequent b^- decay to ¹⁷⁶Hf in the stellar photon bath. This photoexcitation process was studied at the bremsstrahlung facility of the 4.3 MV Stuttgart Dynamitron in combined photon scattering and photoactivation experiments using an enriched ¹⁷⁶Lu sample (72.5%). Numerous new dipole excitations in ¹⁷⁶Lu were observed in the photon scattering experiments performed at bremsstrahlung end point energies of 2.3 and 3.1 MeV. The photoactivation was measured by off-line b- and g-spectroscopy for end point energies from 0.8 to 3 MeV. Evidence was observed for a low-lying intermediate state for the isomer population below 1 MeV. Astrophysical implications will be discussed.

Supported by DFG (contracts Kn 154/31, Pi 393/2 and SFB 634)