The BetaCage, an ultra-sensitive screener for surface contamination

TL;DR

The BetaCage is a proposed ultra-sensitive, nondestructive gaseous neon time-projection chamber designed to detect surface alpha and beta contamination with unprecedented sensitivity for rare-event search backgrounds.

Contribution

This paper introduces the BetaCage detector design, achieving high sensitivity for surface contamination screening through innovative background suppression and detector configuration.

Findings

Sensitivity goals of 0.1 betas per keV-m$^2$-day and 0.1 alphas per m$^2$-day achieved

Backgrounds from detector materials and radon daughters are subdominant

Design details enable discrimination and shielding for ultra-sensitive detection

Abstract

Material screening for identifying low-energy electron emitters and alpha-decaying isotopes is now a prerequisite for rare-event searches (e.g., dark-matter direct detection and neutrinoless double-beta decay) for which surface radiocontamination has become an increasingly important background. The BetaCage, a gaseous neon time-projection chamber, is a proposed ultra-sensitive (and nondestructive) screener for alpha- and beta-emitting surface contaminants to which existing screening facilities are insufficiently sensitive. Sensitivity goals are 0.1 betas per keV-m$^2$-day and 0.1 alphas per m$^2$-day, with the former limited by Compton scattering of photons in the screening samples and (thanks to tracking) the latter expected to be signal-limited; radioassays and simulations indicate backgrounds from detector materials and radon daughters should be subdominant. We report on details of the background simulations and detector design that provide the discrimination, shielding, and radiopurity necessary to reach our sensitivity goals for a chamber with a 95$\times$95 cm$^2$ sample area positioned below a 40 cm drift region and monitored by crisscrossed anode and cathode planes consisting of 151 wires each.