A windowless gas target for low-energy 4He (12C, 16O) γ experiment: improvement to reduce 16O backgrounds

A blow-in type windowless thick He gas target has been developed to measure 4He(12C,16O) γ cross section for astrophysical interests. We use a 12C beam of energy from 6 to 2.8 MeV and detect 16O recoils at forward angles. Numerous 12C backgrounds have been rejected by particle identification techniques. 16O backgrounds from the target are not many but fatally harmful. Our techniques to reduce the 16O backgrounds are described.