CARBON MOLECULAR SIEVE FOR RADON AND THORON MONITORING C. COSMA 1 , A. TIMAR 1 , V. BENEA 1 , I. POP 2 , M. MOLDOVAN 1 1 Faculty of Environmental Science, Babes-Bolyai University Cluj-Napoca, Romania, E-mail: cosmac@enviro.ubbcluj.ro 2 Emanuel University, Oradea, Romania Received November 14, 2008 The charcoals with thermoluminescent detectors, for determination of radon concentrations in air, were studied. For a carbon molecular sieve, the detection limit for indoor radon was 65 Bq/m 3 /day. A linear dependence of detector signal on radon concentration was shown. Key words: radon detection, charcoal adsorption constant, thermoluminescent detectors. 1. INTRODUCTION Many investigations have been performed to determine the radon concentration in the indoor environment or working places [1]. The most used integrating radon detectors are based on the activated charcoal and track etched detectors, respectively. The first type of detector is used for short time measurement, typically, for an exposure time, of few days. The radon concentration in air is obtained by analysing their content in charcoal, as determined by γ-spectroscopy [2–4]. The charcoal method uses detectors having a diffusion barrier between the charcoal and air. As a consequence, the adsorbed radon by charcoal is proportional to the radon concentration in air. The track-etched detector is used for an exposure time of some months. In order to count the α-tracks, the chemical and/or electrochemical etched detectors are used [5]. In order to increase the detector sensitivity, a combined system, using track- etched and charcoal was proposed [6–8]. The detectors used in personal dosimeters must to be active only during working time. In these situations activated charcoal and thermoluminescent (TL) detectors are considered [9, 10]. The humidity variations by using both diffusion and convection of radon adsorption by charcoal were investigated [11]. The detector assembly involves at least two TLDs. One determines the radiation emitted by radon Rom. Journ. Phys., Vol. 54, Nos. 3–4, P. 401–405, Bucharest, 2009