Abstract: Improved circuitry or systems for the continual testing of the ability of a radiation detection system to detect radiation whether the radiation source being used for the testing is located externally to or is located within the same housing as the radiation detector. The improvement includes means for maintaining a constant voltage upon a control member which means provides accomodation for random or spurious radiation by controlled excitation of a radiation source which provides means for monitoring this radiation source for automatically determining the operational condition of the radiation detector.

Abstract: A device for determining that the optical surfaces through which radiation must travel from a hazardous area of radiation to a radiation detector are free from radiation absorbing material or radiation blocking material, the device including an enclosure for commonly housing both a source of and a detector of radiation while isolating the same from each other, preventing radiation transmission within the housing from the source to the detector, such enclosure defining a path for radiation emission from the source outwardly from the housing to a reflective surface or surfaces which surface or surfaces will redirect the radiation back to the detector through the same optical surfaces that radiation from the hazardous area must pass. The relective surface or surfaces may be integral with the enclosure or may be remotely located therefrom.