Surface contamination of 222Rn progeny from the
238U 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
210Pb surface contamination of flat samples. The detection
concept exploits the readout capabilities of the Micromegas
detectors for the reconstruction of 210Po alpha tracks to
increase the signal-to-background ratio. We report here on the
design and realization of a first 26 × 26 cm2
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 210Pb
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 5×10-8 alphas cm-2
s-1. We discuss here the prospects to reach these sensitivity
goals with a radiopure AlphaCAMM prototype currently under
construction.