Investigation of the areas of high radon concentration in Gyeongju

•Preliminary measurements of the indoor radon concentrations were performed at the auditoriums in 23 elementary schools in Gyeongju.•Considering the geological characteristics and preliminary survey results, three elementary schools were screened for closer scrutiny.•For the three schools, continuous measurements were made at their principal's and administration offices over 48-h period.•The scrutiny revealed one elementary school of high radon concentration much higher than the U.S. EPA action level.

The aim of this study was to survey the radon concentrations at 21 elementary schools in Gyeongju, Republic of Korea, to identify those schools with high radon concentrations. Considering their geological characteristics and the preliminary survey results, three schools were finally placed under close scrutiny. For these three schools, continuous measurements over 48 h were taken at the principal's and administration office. The radon concentrations at one school, Naenam, exceeded the action level (148 Bq/m3) established by the U.S. EPA, while those at the other two schools were below that level.