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HK: Hadronen und Kerne

HK 39: Nuclear Astrophysics III

HK 39.3: Gruppenbericht

Dienstag, 17. März 1998, 17:30–18:00, E

Investigation of the reactions ¹⁹F(p,αγ)¹⁶O and ¹⁹F(p,γ)²⁰Ne relevant for the recycling/breakout of the CNO cycles 1.0mm♣ — •J.W. Hammer¹, R. Ott¹, G. Bulski², M. Jaeger¹, A. Mayer¹, R. Kunz¹, R. Morlock¹, G. Staudt³, K. Spyrou⁴, Ch. Chronidou⁴, S. Harissopulos⁴, T. Paradellis⁴, H. Schulte⁵, and C. Rolfs⁵ — ¹Inst. f"ur Strahlenphysik, Univ. Stuttgart, D–70550 Stuttgart — ²Fa. DANET GmbH., Waldburgstraße 17–19, D–70563 Stuttgart — ³Physikal. Inst., Univ. Tübingen, D–72076 Tübingen — ⁴Inst. of Nuclear Physics, N.C.S.R. “Demokritos”, Gr–15310 Athens — ⁵Inst. für Experimentalphysik 3, Univ. Bochum, D–44780 Bochum

Hydrogen burning stars of the second or third generation with masses larger than the sun, produce energy faster by the standard CNO cycle which has four reaction loops. At the outer loop ¹⁹F can react into two directions, one branch is recycling via ¹⁹F(p,αγ)¹⁶O and the other is a breakout via ¹⁹F(p,γ)²⁰Ne into the NeNa-cycle with no return. The reaction rates at burning temperatures are uncertain because of the lack of reliable data of both branches at low energies.
Now new data are available measured in some experimental approaches with quite different concepts. In a first set of experiments angular distributions and excitation functions of all subbranches pα₀, pα₁, pα₂, pα₃, pα₄; pαγ₂, pαγ₃, pαγ₄; pγ₀ and pγ₁ have been measured in inverse kinematics using a ¹⁹F^x+ beam (x=1-4). There was no possibility to construct a pure fluorine target. In a second set, using solid state targets, several particle detectors and two high resolution γ-detectors at 0^∘ and 90^∘, excitation functions of the subbranches pα₀, pαγ₂, pαγ₃, pαγ₄, pγ₀ and pγ₁ were observed. The aim of these two sets of experiments was to get as far as possible the complete differential information for the reaction in order to describe the reaction mechanism by the R-matrix formalism.
The concept of the third set of experiments was to avoid the problems of a differential measurement by measuring the total γ-transition-rate in 4π without discrimination of subchannels. The γ-detection was performed by using large 4π-NaJ-detectors which were summing up the cascade transitions with high efficiency.
The experiments on both reactions have been performed at the Dynamitron accelerators of Bochum and Stuttgart and at the tandem of Demokritos, Athens.
The data have been analyzed and a good agreement is observed between the different results. The actual situation concerning cross sections, resonances, S-factors and reaction rates will be presented.
1.0mm♣ Work supported by Deutsche Forschungsgemeinschaft (DFG) HA 962, Bonn