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a television camera tube; a variety of vidicon, but with a different type of photosensitive target. The plumbicon target consists of a layer of lead oxide, PbO, which is deposited by thermal evaporation in a rarefied gaseous medium on a transparent film of tin dioxide, Sn02, that serves as the signal plate of the device.
After treatment of the layer with a gas discharge in oxygen, the plumbicon target has a complex semiconductor structure with three conductivity regions—electron (n), intrinsic (i), and hole (p) conductivity—in a total thickness of 15–20 microns; that is, it has the structure of a p-i-n diode. When a positive voltage is applied to the signal plate and the target is exposed to an electron beam, the diode becomes reverse-biased in the beam circuit (the diode is cut off), and there is virtually no current in the circuit of the signal plate. This current, called the dark current, usually does not exceed 10–9 to 10–10 ampere. However, when the image being transmitted is projected onto the target from the direction of the signal plate, current carriers (electron-hole pairs) are created in the i-region by the action of the light, and current flows in the signal-plate circuit. The strength of the current is proportional to the illuminance on the part of the target where the electron beam is incident.
The main advantages of the plumbicon are the weak signal in the dark; the low inertia; the closeness of the tube’s spectral response to the visibility curve for monochromatic radiation (the ability of the human eye to perceive such radiation), which ensures the proper reproduction of colored images; and the linearity of the “light-signal” response. These qualities determine the major area of use of the plumbicon (in color television cameras).
REFERENCEHaan, E., A. Drift, and P. P. M. Schampers. “The ‘Plumbicon,’ a New Television Camera Tube.” Philips Technical Review, 1963–64, vol. 25, nos. 6–7.
A. IU. KATSMAN