A high-sensitivity large volume cryogenic detector for radon in gas

A new detector for 222Rn measurements in gases is described. It is based on the low temperature collection of radon on a stainless steel plate and subsequent counting of emitted alpha particles using an ion-implanted silicon detector. A very low background of 25 counts/day for the 222Rn energy window was achieved. High detection efficiency of 32 % (2. geometry) and the large 65 liter volume of the detector allow radon measurements at the level of 12 mBq/m3 with 30 % accuracy (relative error). Behavior of the alpha emitting radon daughters born on the cooled stainless steel plate, 218Po and 214Po, was also analyzed