hypersensitization


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hypersensitization

(hÿ-per-sen-să-ti-zay -shŏn) The subjection of an unexposed photographic emulsion to one or more methods of treatment in order to improve its response to light or other radiation. This allows the emulsion to be used at the extremely low intensities of light and other electromagnetic radiation encountered in astronomy without an excessively long exposure time. Alternatively in a set period of telescope time the quantity or quality of information obtained can be increased by hypersensitization. Various techniques are used. One particularly suitable for light-sensitive emulsions is gas hypersensitization (or hypering). It involves heating the emulsion in either pure nitrogen gas or in nitrogen with a small admixture of hydrogen. The gas removes oxygen and water vapor from the emulsion; these impurities act as desensitizers. Heating speeds up this leaching process and can also increase the chemical sensitization, i.e. the possibility that grains in the emulsion if hit by light will be activated.

Hypersensitization

 

a method of increasing the speed of a silver halide photographic material by washing it in water, an aqueous or aqueous-ammonia solution of silver nitrate, or a solution of triethanolamine. Hypersensitization can increase sensitivity severalfold, especially in the case of infrachromatic materials. The possibilities of hypersensitization are quite limited, however, largely because it must be carried out immediately before exposure. The effect of hypersensitization is manifested more in the region of additional sensitivity of the photographic material (caused by the presence in the emulsion of molecules of a sensitizer-dye) than in the region of the material’s own sensitivity (caused by the properties of the silver halide itself); it also appears at long exposure times and for low illumination on the layer. The nature of hypersensitization consists first in reducing the concentration in the emulsion layer of bromine ions, which reduce the photosensitivity of the layer but heighten the selectivity of the developer, and second in removing from the surface of the silver halide crystals oxidized molecules of the sensitizer-dye that have been adsorbed by it.

IU. N. GOROKHOVSKII

hypersensitization

[¦hī·pər‚sen·sə·tə′zā·shən]
(graphic arts)
Any of various techniques for increasing the sensitivity of a photographic plate; includes chemical treatments, removal of oxygen and water, baking, soaking in hydrogen gas, preflashing, and push development.
(immunology)
The process of producing hypersensitivity.
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