Sensitivity of LR 115 detectors in hemispherical chambers for radon measurements

We have determined the detection sensitivity of the LR 115 detector placed on the bottom of hemispherical diffusion chambers through Monte Carlo simulations. For the cases where the LR 115 detectors completely cover the bottom of hemispherical diffusion chambers, we propose the optimum radius of the hemispherical chamber as 3 cm. In hemispherical chambers with radii smaller than 3 cm, the total sensitivity is smaller which will lower the number of tracks and increase the statistical uncertainty. On the other hand, if the radius is larger than 3 cm, the effects of the deposition fraction of radon progeny will come into effect, which will again introduce uncertainties in radon measurements. For the hemispherical chamber with a radius of 3 cm, we further propose the detector radius to be 1.3 cm. This combination will eliminate the influence of the deposition fraction on the total sensitivity and at the same time give a large total sensitivity. For a detector with this radius, the hemispherical chamber with a radius of 3 cm is the largest one which provides the total sensitivity independent of the deposition fraction of radon progeny. 2003 Elsevier B.V. All rights reserved. PACS: 29.40; 23.60