GB1299459A - Long persistency photoelectric storage target - Google Patents

Abstract

1299459 Photochromic materials and uses thereof ORGANIZATION EUROPEENNEDE RECHERCHES SPATIALES 9 April 1970 16985/70 Heading C4S [Also in Division H1] A photo-electric storage target comprises a crystalline radiation-sensitive storage film of an alkali halide deposited on a low work function caesium layer on a transparent substrate. In Fig. 3 the target comprises a fibre-optics plate 1 coated on one side with a caesium layer 2, an alkali halide layer 3, and a film 4 adapted to reduce the electron affinity of the exposed surface of the layer 3; this film may be of caesium or barium, a caesium compound, a metal oxide, or an absorbed gas. The target is charged by electrons from a photo-cathode 31 and then rotated through 90 degrees for reading by means of a reading gun 42 which scans a luminescent coating 6 arranged over a transparent conductive or semi-conductive layer 5; the light spot causes photo-emission from the opposite side of the target into an electron multiplier output 43. The reading is non-destructive, and the charge is erased by illumination with white light. The layers 5 and 6 may be omitted and the light for reading the charge image produced in a different way (Fig. 1, not shown); the target surfaces may be plane instead of curved (Figs. 1 and 2, not shown). The target may be used as a photo-cathode in a demountable tube; it is activated by X-rays, gamma rays or other ionizing radiation, and is then sensitive to light of a wavelength corresponding to the absorption bands of the induced colour centres. Similarly the target may be used as a radiation detector.