Abstract: A radon detector including a base portion, a cover portion, and a shield arrangement. The cover portion attached to the base portion houses a contained gas volume and allows diffusion of gas between a surrounding into the contained gas volume. The base portion has at least two detector location areas, enabling mechanical arranging of nuclear track detector means. The shield arrangement includes at least one shield and a shield actuator arranged for moving the shield between a closed and an open position, for each of the detector location areas. Thereby, the shield in the closed position prevents a line-of-sight between the contained gas volume and the detector location area. The shield in the open position allows a line-of-sight between the contained gas volume and the detector location area. The shield actuator is controllable from outside the contained gas volume.