Radiation Measurements 42 (2007) 286 – 289 www.elsevier.com/locate/radmeas Seasonal variation of indoor air radon concentration in schools in Kosovo M. Bahtijari a , P. Stegnar b , Z. Shemsidini a , H. Ajazaj a ,Y. Halimi c , J. Vaupotiˇ c b , I. Kobal b, ∗ a Faculty of Education, University of Prishtina, Kosovo b Randon Center, Jožef Stefan Institute, P.O. Box 3000, 1001 Ljublajna, Slovenia c Faculty of Medicine, University of Prishtina, Kosovo Received 25 November 2005; received in revised form 30 August 2006; accepted 29 September 2006 Abstract Indoor air radon ( 222 Rn) concentrations were measured in March, May, August and December in 15 rooms of five elementary and in six rooms of one high school in Sharr, Kosovo, using alpha scintillation cells. Only in one room did the value exceed 200Bq m -3 . Values decreased from December to August, and from basement to first floor. © 2006 Elsevier Ltd. All rights reserved. Keywords: Radon; Scintillation cells; Indoor air; Schools; Concentrations; Seasonal variation 1. Introduction More than half the annual effective dose received by a mem- ber of the general public from all natural radioactive sources originates from the radioactive noble gas radon and its short- lived decay products. For this reason, the problem of indoor radon has attracted great attention worldwide, and many coun- tries have carried out nation-wide radon surveys (UNSCEAR, 2000). Although the first radon measurements in Kosovo were made in the course of prospecting for uranium in the period 1983–1989 (Jakupi et al., 1989), it was ten years later when monitoring of indoor radon in dwellings was started (Jakupi et al., 1997). Radon concentrations obtained by exposing track etched detectors (Šutej et al., 1988) in 83 buildings varied in the range of 20.100 Bq m -3 (with an average value of 50 Bq m -3 ) in the cities of Prishtina and Brezovica, while in houses in the suburbs of Prishtina, lying over a lignite layer, the values were in the range of 150.450 Bq m -3 . Values of more than 1000 Bq m -3 were found in several houses built of stone in Gornja Stubla town, where elevated radon levels in soil gas had been found during uranium prospecting. In order to make the radon map more complete, a decision was made in 2002 to carry out an indoor radon survey in the entire territory of ∗ Corresponding author. Tel.: +386 1 477 3239; fax: +386 1 477 3811. E-mail address: ivan.kobal@ijs.si (I. Kobal). 1350-4487/$ - see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2006.09.001 Kosovo. The survey will be carried out in steps, lasting several years, following the experience gained in Slovenia ( Vaupotiˇ c et al., 2000). Starting with public buildings, such as kinder- gartens and schools, monitoring will be continued in other en- vironments potentially exposed to radon, such as karst caves, water works and other underground workplaces. In this sur- vey, scintillation cells will be used for fast screening purposes, while etched track detectors will be exposed to obtain average radon concentration. In this paper, we report on indoor radon concentrations in el- ementary and high schools in Sharr, Kosovo, with the emphasis on their seasonal variations. 2. Experimental 2.1. Measuring sites The town of Sharr with 12,300 inhabitants is located in the southern part of Kosovo. Altogether, there are five elementary and high schools, of which six with 3631 pupils and one with 786 students, respectively, were included in this study. They are mostly single-storey buildings, some with a basement, some without. All were built after 1974, of stone and brick, and recently of prefabricated elements. Climate in the region is typically continental, with severe winters and hot summers. In some buildings rooms are heated individually by burning