Characteristics of a new high-sensitivity X-ray imaging tube for video topography

A new type of high-sensitivity X-ray imaging tube having an amorphous selenium photoconductive layer with a thickness of 8 µm has been fabricated. Signal charges induced by X-ray photons can be avalanche-multiplied in the photoconductive layer under a large electric field. The sensitivity of the tube reaches the level of individual X-ray photon detection. For the detection of such a small number of X-ray photons, a new kind of noise is generated due to the fluctuation of absorption depth in the photoconductive layer under the operation conditions of avalanche multiplication. Signal-to-noise ratio can be improved by the accumulation of signal charges in the photocon-ductive layer. An example of real-time X-ray topography by weak X-rays using this experimental tube is demonstrated.