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

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 $5\times 10^{-8}$ alphas cm${}^{-2}$ s${}^{-1}$. We discuss here the prospects to reach these sensitivity goals with a radiopure AlphaCAMM prototype currently under construction.

Prepared for submission to JINST

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