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Köln 2004 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 34: Nuclear and Particle Astrophysics II

HK 34.3: Talk

Wednesday, March 10, 2004, 14:45–15:00, F

Photoactivation and photon scattering experiments on the stellar thermometer 176Lu — •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, and K. Wisshak41Inst. 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; t1/2=3.635 h) in 176Lu and its subsequent β 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 β- and γ-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)

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