The SuperNEMO experiment is devoted to neutrinoless double beta decay detection and main R&D of the detector design is already finished. The crucial role in such low background experiments plays the suppression of background. One of the most important sources of radioactivity is the radon gas and its daughter products. The radon activity in the volume of the detector will be reduced significantly using the antiradon facility already installed in the Modane underground laboratory which provides air with a radon volume activity at the order of ∼mBq/m 3 . To be able to measure low radon activities at the output of this antiradon facility in reasonable time of measurement the develoment of new ultra-sensitive radon detector is currently carried out. The detection is based on electrostatic collection of radon progenies ( 214 Po, 218 Po) on a Si PIN diode. Our idea is to increase the volume of the detector up to 1 m 3 divided into smaller subdetectors (50-100 l) to improve the detection effectiveness and consequently the sensitivity. Two prototypes of sensitive radon detectors were constructed (50 l and 300 l). Preliminary results of the detection efficiency and the background measurement for the first prototype are also presented.

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In a spectroscopic study of non-irradiated and proton-irradiated silicon diodes, the detectors were illuminated from the front side and from the rear side by various alpha particle sources (mainly ThC') and by monoenergetic protons with energies from 1.0 to 2.5 MeV. Their response characteristics have been studied as a function of the incoming particle energy and the applied bias voltage. The charge collection eciency was determined as a function of uence.

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