Understanding photoneutron sources for ultra-low background astrophysics measurements

The ¹³C(α,n) and ²²Ne(α,n) reactions, fueling the main and weak components of the s-process, are a top priority of current and upcoming underground astrophysical labs. This is driven by the need for ultra-low-background environments required for performing these very low yield measurements into the stellar burning regimes.  Critical to the success of these measurements will be the characterization of ambient and beam-induced neutron background sources.  One such background is photoneutron production from deuterium, induced by high-energy (>2.2 MeV) gamma rays, from beam-induced reactions or environmental background.  A set of controlled experiments was performed at Oak Ridge National Laboratory and the CASPAR facility at SURF in an attempt to understand the impact of this reaction.  Results of this study and implications for neutron counting and quasi-spectroscopic measurement approaches will be discussed.