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HK: Hadronen und Kerne

HK 39: Nuclear Astrophysics III

HK 39.5: Vortrag

Dienstag, 17. März 1998, 18:15–18:30, E

Helium Burning of ²²Ne: The Reaction ²²Ne(α,γ)²⁶Mg — •M. Jaeger¹, J. W. Hammer¹, A. Mayer¹, R. Kunz¹, R. Morlock¹, V. Koelle², and G. Staudt² — ¹Institut f"ur Strahlenphysik, Universit"at Stuttgart, D-70569 Stuttgart — ²Physikalisches Institut, Universit"at Tübingen, D-72076 Tübingen

The site of the s-process is the helium burning shell of a pulsating red giant [1], and a favorite neutron source for this process is the reaction ²²Ne(α,n)²⁵Mg. The importance of this neutron source depends on the abundance of ²²Ne, the reaction cross section at the energies of interest, and also on the competing reaction ²²Ne(α,γ)²⁶Mg. In a first experiment, we investigated the (α,γ)-reaction in the projectile energy range from 640 to 1440 keV. For our study the 4 MV Dynamitron accelerator in Stuttgart was used in connection with the windowless gas target system RHINOCEROS. The γ–rays were observed with two 100 % Ge detectors placed at an angle of 90^∘ to the beam direction, both surrounded with a BGO-shielding. Using a new BGO-shielding, it was possible to place one of the detectors in a close geometry to the beam axis. With this setup the sensitivity limit is improved compared to previous measurements [2] by about one order of magnitude. In the (α,γ)-reaction we studied up to now two known resonances at E_α= 828 and 1434 keV and in the energy region below 828 keV upper limits have been determined.

[1] I. Iben, Ap. J. 196, 525, 549 (1975)

[2] A. Wolke, Z. Phys. A334, 491–510 (1989)