SaG4n: Calculation of (alpha,n) yields for low background experiments using Geant4

SaG4n is a code fully based on Geant4 that we have developed to calculate neutron yields. The code is available in http://win.ciemat.es/SaG4n and works for Geant4.10.6 or superior. The improvements to the (alpha,n) yields introduced by the use of a single Monte Carlo code, fully developed in Geant4, are presented. Neutrons are a potential source of background for all rare-event searches, and is specially relevant for WIMP searches with liquid argon, where they are the only source of irreducible background together with the yet-negligible coherent neutrino scattering. The precision of the neutron yield is critical to evaluate the discovery potential of coming experiments and to reduce systematic effects in current data. We present the result of evaluating the neutron yield for three different cases and show the sizable effect of interfaces between materials with high (alpha,n) cross section and materials with small mass which contribution to the neutron budget is often considered negligible.