The instant invention relates to a method and an apparatus of monitoring nuclear radiation. The method utilizes a diamond radiation sensor element having a nitrogen impurity concentration of less than 150 ppm. The sensor element is subjected to nuclear radiation, while being stimulated with light of a selected wavelength or range of wavelengths, preferably in the ultraviolet or near-ultraviolet range, resulting in light emissions from the sensor element. Typically, the sensor element is fixed to the end of an optical fibre, the far end of the fibre being used to channel stimulating light to the sensor element and to feed resultant light emissions from the sensor element to a photomultiplier tube.