A radon detector , comprising: - a base portion ; - a cover portion , arranged for being removably attached to said base portion ; said cover portion , when being attached to said base portion , housing a contained gas volume between said cover portion and said base portion ; said cover portion and said base portion , when being attached to each other, allowing diffusion of gas between a surrounding into said contained gas volume ; said base portion having at least two detector location areas , each of said two detector location areas being provided with a track detector means , enabling mechanical arranging of nuclear track detector means to said base portion ; and - a shield arrangement , comprising at least one shield and a shield actuator ; said shield actuator being arranged for mechanically moving a shield of said at least one shield between a closed position and an open position, for each of said detector location areas ; wherein said shield of said at least one shield in said closed position of a respective said detector location area prevents a line of sight between at least a part of said contained gas volume and said respective said detector location area and wherein said shield of said at least one shield in said open position of said particular detector position allows a line of sight between said at least a part of said contained gas volume and said respective said detector location area ; said shield actuator being controllable from outside said contained gas volume , characterized in that said shield actuator being arranged for mechanically moving said shield of said at least one shield between a closed position and an open position, for each of said detector location areas , so that a closing of one detector location area is connected to an opening of another detector location area. - a base portion ; - a cover portion , arranged for being removably attached to said base portion ; said cover portion , when being attached to said base portion , housing a contained gas volume between said cover portion and said base portion ; said cover portion and said base portion , when being attached to each other, allowing diffusion of gas between a surrounding into said contained gas volume ; said base portion having at least two detector location areas , each of said two detector location areas being provided with a track detector means , enabling mechanical arranging of nuclear track detector means to said base portion ; and - a shield arrangement , comprising at least one shield and a shield actuator ; said shield actuator being arranged for mechanically moving a shield of said at least one shield between a closed position and an open position, for each of said detector location areas ; wherein said shield of said at least one shield in said closed position of a respective said detector location area prevents a line of sight between at least a part of said contained gas volume and said respective said detector location area and wherein said shield of said at least one shield in said open position of said particular detector position allows a line of sight between said at least a part of said contained gas volume and said respective said detector location area ; said shield actuator being controllable from outside said contained gas volume , characterized in that said shield actuator being arranged for mechanically moving said shield of said at least one shield between a closed position and an open position, for each of said detector location areas , so that a closing of one detector location area is connected to an opening of another detector location area. <EOS>