Radon isotopes occur in the natural radioactive decay series of uranium (U-235 and U-238) and thorium (Th-232), which exist in the earth's crust with varying concentrations in different locations. It is believed that underlying soil is the main source of radon in the atmosphere of dwellings, offices and public places. In view of the risk presented by high concentrations of radon and its progeny indoors, this work was carried out to measure radon concentration in different types of soil in the northern part of Jordan at different depths (0, 25, 50, 75 and 100 cm). The prepared time-integrated passive dosimeters were distributed among eight stations located in the governorate of Irbid. The results of this study show that the radon levels at a given depth vary significantly from one type of soil to another. For example, at 100 cm depth radon levels range from 4000 Bq/m(3) in limestone to 4 x 10(5) Bq/m(3) in chalky marl. Moreover, we found that the radon concentration increases exponentially with depth, which is in good agreement with a mathematical model. Therefore, it is strongly recommended that houses should not be constructed on such soil if U/Th-rich bedrock lies underground.
