Abstract.A cross section measurement employing a direct 16 O detection method for the reaction energies from E cm = 2.4 to 0.7 MeV is planned at Kyushu University Tandem Laboratory (KUTL). To perform this experiment and to obtain quantitative information about the cross section to within an error of 10%, we have developed several instruments, including a blow-in type windowless gas target, a recoil mass separator and a RF-deflector. The measurements at E cm = 2.4 and 1.5 MeV have been performed with these instruments. For measuring at E cm < 1.2 MeV, a hybrid detector employing both, an ionization chamber and a silicon detector was developed to reduce the carbon backgrounds more efficiently. The oxygen ions were clearly separated from carbon background by using the energy deposit in the ionization chamber. Experiment of E cm = 1.2 MeV was performed and the cross section was obtained.
O+γ is one of the main reactions in He-burning of stars and important for nucleosynthesis. The fusion cross section at stellar energy of E cm = 0.3 MeV has not been determined precisely yet in spite of efforts for about 40 years. We plan to measure directly the total fusion cross section down to 0.7 MeV at Kyushu University Tandem accelerator Laboratory and to estimate the cross section at 0.3MeV by extrapolation. We have already measured the cross sections at 2.4 MeV and 1.5 MeV. The measurement at E cm =1.2 MeV is in progress.
Direct measurement of 12 C+ 4 He 16 O+ total cross section was made at E cm = 2.4, 1.5 and 1.2 MeV, and preliminarily measurement was made at 1.0 MeV. A thick windowless 4 He target was developed and the low-energy 12 C beam intensity was increased by modifying our tandem accelerator. 16 O recoils were detected after removing large 12 C backgrounds. Remaining obstacle is 16 O backgrounds produced by stray beams. Prospects for future experiments of 12 C+ 4 He 16 O+ cross section down to E cm =0.7 MeV are presented.
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