Abstract
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.