Nozomi Oba

Background reduction system of 4He(12C, 16O)γ at KUTL

The C‐alpha reaction is one of the most important reactions in astrophysics. At Kyushu University Tandem accelerator Laboratory (KUTL), a high detective efficiency measurement has been made by adopting inverse kinematics: 12C beam is injected on windowless 4He gas target. In this experiment, a powerful background reduction system is necessary. We describe the effectiveness of the background system consisting of recoil mass separator, a long time chopper, and new movable slits.

Direct measurement of 4He(12C,16O)γ reaction at KUTL

A 12 C + 4 He → 16 O +γ is regarded as the very important reaction to know the evolution of heavy stars. The cross section is, however, still unknown in spite of more than 40 years experiment in the world because of an existence of a resonance state of 16 O at sub‐threshold region. A cross section measurement with the direct detection of the produced 16 O from E cm = 2.4 downto 0.7 MeV have been planned at Kyushu University Tandem Laboratory(KUTL). Detection of the 16 O is the most possible method at low energy, since a detection efficiency of the 16 O is very high. The new windowless blow‐in gas target was developed to achieve the pressure of 24 Torr. Many movable slit were installed in a recoil mass separator, so that the backgrounds generated by the 12 C beam was eliminated effectively. The results of recent experiments at E cm = 2.4 and 1.5 MeV are reported.

Direct measurement of 4He(12C, 16O)γ reaction near stellar energy

A cross section measurement with a direct 16O detection method for the reaction energy from Ecm = 2.4 down to 0.7 MeV is planned at Kyushu University Tandem Laboratory (KUTL). To perform the experiment successfully and to get the quantitative information of the cross section within the 10% error, we have newly developed several instruments in 2009, such as a blow‐in type windowless gas target and movable slit system placed in the recoil mass separator. By using the windowless blow‐in gas target, a pressure of 24 Torr was achieved. The effective thickness along the beam axis was measured by p+4He scattering. Thanks to the movable slits installed in a recoil mass separator and the trajectory analysis, we found effective reduction of background conditions from the 12C beam.