Improvement and Characterization of HIgh Pressure POint-like Gas Jet Target (HIPPO)

Accurate characterization of a target in experimental nuclear astrophysics is imperative because calculations and analysis depend heavily on the number of atoms in the target. Traditional setups studying alpha capture reactions, for example, use a solid, well-understood target and a light ion beam such as 4He. However, background radiation often overshadows the gamma rays that are the signature of the reaction. Inverting the experimental setup, such that a "heavy" ion beam bombards a "light" helium gas target, allows for the detection of the heavy recoil instead of detecting the gamma rays alone. The St. George separator of the 5U nuclear accelerator at the University of Notre Dame uses a HIgh Pressure POint-like gas jet target (HIPPO) to maintain a stable target of helium, such that inverse kinematics measurements, with a heavy beam, can be performed. The thickness of the gas target, however, varies with the gas injection pressure and residual gas may contaminate the gas makeup. By developing and installing a remote interface for a mass flow controller and a liquid nitrogen autofill system for a sorption cold trap, we were able to improve the injection pressure stability, as well as the purity of the gas makeup. With the cleaned and stabilized helium target, we will next use elastic scattering measurements in inverse kinematics, to characterize the thickness of the target. Consequently, we will be able to make more precise measurements and reliable conclusions in future experiments with St. George.