Device and method for determining a density of a radical in a gas

Device (10) for determining a density of radicals (5) of a radical type in a measuring space (4), wherein the device comprises: - a catalyst material (1) which can be brought into contact with the measuring space at least in the region of a first surface (15) of the catalyst material, wherein the catalyst material is suitable for triggering an exothermic recombination reaction of radicals of the radical type when radicals of the radical type come into contact with the first surface, - a temperature actuator (2) in thermal contact with the first surface, and - a temperature sensor (3) in thermal contact with the first surface, wherein the device is designed to control the temperature actuator by means of a control signal in such a way that the measured value detected by the temperature sensor is kept at a setpoint value, and wherein the control signal can be evaluated in order to determine the density of radicals of the radical type in the measuring space. The invention is further directed to a method for dete