AlphaCAMM, a Micromegas-based camera for high-sensitivity screening of alpha surface contamination

TL;DR

AlphaCAMM is a novel gaseous Micromegas-based camera designed for high-sensitivity detection of $^{210}$Pb surface contamination, improving background discrimination in rare event search experiments.

Contribution

This work introduces AlphaCAMM, a new Micromegas-based detector with a specialized alpha track reconstruction algorithm for direct surface contamination measurement.

Findings

Demonstrated the detection concept with a 26x26 cm² prototype.

Achieved a detection sensitivity goal of 100 nBq/cm² for $^{210}$Pb.

Outlined prospects for reaching ultra-low background levels with a radiopure prototype.

Abstract

Surface contamination of $^{222}$Rn progeny from the $^{238}$U natural decay chain is one of the most difficult background contributions to measure in rare event searches experiments. In this work we propose AlphaCAMM, a gaseous chamber read with a segmented Micromegas, for the direct measurement of $^{210}$Pb surface contamination of flat samples. The detection concept exploits the readout capabilities of the Micromegas detectors for the reconstruction of $^{210}$Po alpha tracks to increase the signal-to-background ratio. We report here on the design and realization of a first 26$\times$26 cm$^2$ non-radiopure prototype, with which the detection concept is demonstrated by the use of a new algorithm for the reconstruction of alpha tracks. AlphaCAMM aims for minimum detectable $^{210}$Pb activities of $100$ nBq cm$^{-2}$ and sensitivity upper limits about $60$ nBq cm$^{-2}$ at 95\% of C.L., which requires an intrinsic background level of $5\times10^{-8}$ alphas cm$^{-2}$ s$^{-1}$. We discuss here the prospects to reach these sensitivity goals with a radiopure AlphaCAMM prototype currently under construction.