Abstract
As a link between the NeNa and MgAl cycles in stellar burning, the reaction 23 Na(p,γ )24 Mg is of interest for various astrophysical scenarios, such as AGB stars. A combined effort at the Laboratory for Underground Nuclear Astrophysics (LUNA) and the Nuclear Science Laboratory (NSL) at the University of Notre Dame aims at a cross section determination for the this reaction, to constrain the astrophysical reaction rate by improving the knowledge of the resonance strengths and the non-resonant component. Experiments at LUNA benefit from the underground location at the Gran Sasso National Laboratory which allows for the measurement of resonances at low energies with high sensitivity in a low background environment. Measurements at the University of Notre Dame pursue a determination of the non-resonant cross section at higher energies. We present the two experiments and the status of the data analysis.
Highlights
The reaction 23Na(p, γ)24Mg links the NeNa and MgAl cycles in stellar hydrogen burning
For temperatures up to approximately 100 MK, typical for Red Giant Branch (RGB) and low and intermediate mass Asymptotic Giant Branch (AGB) stars, the rate of this reaction is predominantly determined by the non-resonant component of the cross section and possibly by a narrow resonance at Ec. m. = 138 keV [1]
We used two complementary detector setups to study the 23Na(p, γ)24Mg reaction underground at Laboratory for Underground Nuclear Astrophysics (LUNA): one setup employed a segmented BGO summing-detector [4] with high efficiency but modest energy resolution (e. g. about 4-5% energy resolution and 60% full energy detection efficiency for e-mail: axel.boeltzig@nd.edu a single 12 MeV gamma ray), the other setup used a HPGe detector (ORTEC GEM120225-P-ST, located at 55◦ relative to the beam) that offered much better energy resolution but lower efficiency and angular coverage than the first setup
Summary
The reaction 23Na(p, γ)24Mg links the NeNa and MgAl cycles in stellar hydrogen burning. For temperatures up to approximately 100 MK, typical for Red Giant Branch (RGB) and low and intermediate mass Asymptotic Giant Branch (AGB) stars, the rate of this reaction is predominantly determined by the non-resonant component of the cross section and possibly by a narrow resonance at Ec. m. = 138 keV [1]. = 240 keV starts to become more influential. The non-resonant cross section of 23Na(p, γ)24Mg has not been observed in a direct experiment yet (cf [3]). The uncertainty of these two contributions to the cross section yields large uncertainties in the astrophysical reaction rate in the temperature range given above
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