The BetaCage: Ultrasensitive Screener for Radioactive Backgrounds

Rare event searches, such as dark matter detection and neutrinoless double beta decay, require screening of materials for backgrounds such as beta emission and alpha decaying isotopes. The BetaCage is a proposed ultra-sensitive time-projection chamber to screen for alpha-emitting and low energy beta-emitting (10-200 keV) contaminants. The expected sensitivity is 0.1 beta particles $(per keV-m^2-day)$ and 0.1 alpha particles $(per m^2-day)$, where the former will be limited by Compton scattering of external photons in the screening samples and the latter is expected to be signal-limited. The prototype BetaCage under commissioning at South Dakota School of Mines & Technology is filled with P10 gas (10\% methane, 90\% argon) in place of neon and is 40 x 40 x 20 cm in size. Details on design, construction and characterization will be presented.