A blow-in type windowless gas target for astro-nuclear experiments

A blow-in type windowless gas target (BIGT) has been developed for nuclear experiments near stellar energy, especially for a 4He+12C→16O+γ experiment. The target has a multi-layer structure for differential pumping. Cooling of the target by liquid nitrogen was tried, and the target thickness was found to increase only 1.2 times under a constant gas flow rate. The present target thickness along a beam axis is 1.5 kPa×2.94 cm, which is about a half of our goal. A gas target having very thin windows was also developed using a 50 nm thick silicon nitride foil.