München 2006 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 26: Kern- und Teilchen-Astrophysik

HK 26.1: Vortrag

Dienstag, 21. März 2006, 17:00–17:15, E

Activation Measurements of the ²⁷Al(n,γ)²⁸Al and ²³Na(n,γ)²⁴Na Cross Sections at kT=25 keV — •Ethan Uberseder, Michael Heil, and Franz Kaeppeler — Forschungszentrum Karlsruhe, Postfach 3640, 76021 Karlsruhe

New measurements of the ²⁷Al(n,γ)²⁸Al and ²³Na(n,γ)²⁴Na cross sections have been done with the Karlsruhe 3.75 MV Van de Graaff accelerator. The activations used the ⁷Li(p,n)⁷Be reaction as a neutron source, creating a quasi-stellar neutron spectrum at kT=25 keV. While the half life of ²⁴Na allowed for the employment of the standard activation technique, the short half life of ²⁸Al necessitated the use of the fast cyclic activation method. ²⁷Al and ²³Na are considered to be neutron poisons for the s-process, thus an accurate determination of their neutron capture cross sections at stellar temperatures is vital for models of nucleosynthesis. Preliminary results yield a lower cross section for both isotopes in comparison to previous time of flight measurements. The uncertainties are expected to be within 6 percent. The astrophysical implications of these new values on the stellar models of nucleosynthesis are discussed.