Patent ID: 7368707

Claim:
A radiation detector for detecting ionizing radiation having a wavelength within a first range, said radiation detector comprising: detecting means responsive to said ionizing radiation incident thereon, for generating an output signal indicative of said ionizing radiation; and self-testing means for determining that said detecting means continues to operate properly to detect ionizing radiation, said self testing means comprising, a photoemissive material in communication with the detecting means; a controllable light source for supplying nonionizing radiation of a known wavelength to the photoemissive material, which known wavelength is within a second range that differs from said first range, whereby ionizing radiation is emitted by the photoemissive material in response to the provision of said nonionizing radiation, said ionizing radiation impinging on the detecting means; and control means for supplying activation energy to the light source at predetermined intervals, monitoring the output of the radiation detector to detect any measurement pulses corresponding to activation of the radiation detector by the activation of the light source, deciding in response to such detection that the radiation detector is satisfactorily responsive to ionizing radiation, and deciding, in the absence of such detection that the radiation detector has a fault.