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

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