Design and Deployment of the Directional Beta Source for the Eos Experiment

Eos is a multi-ton scale technology demonstrator for hybrid neutrino detection with water-based liquid scintillator (WbLS) that harnesses the benefits of both Cherenkov and scintillation light. The directionality of Cherenkov light and high yield of scintillation light could improve sensitivity and background rejection for a broad range of neutrino measurements. Eos is the first purpose-built hybrid detector for low-energy event characterization, as well as a testbed for novel technologies. To show that the detector does leverage the Cherenkov signal, it is important to demonstrate its directional reconstruction capabilities. To accomplish this, we have designed and built a novel directional beta source, which has been deployed in Eos. It consists of a small capsule containing either ⁹⁰Sr or ¹⁰⁶Ru, to create a collimated beam of electrons. The calibration source has self-triggering capabilities and produces several Hz of tagged events. The self-shadowing of the source can lead to bias in direction reconstruction, which is an effect that needs to be understood. The source was designed in three different sizes to explore this effect. In this talk, I will present the design of the directional beta source and its deployment in Eos.