. Dental and oral radiography; a textbook for students and practitioners of dentistry . Fig. 25.—Diagram of an x-ray tube. The hemisphere in front of the target which is the activehemisphere, is evidenced by a green fluorescence, theshade of coloring depending upon the degree of vacuumof the tube. The fluorescence of a highly exhausted tubewill be a light yellowish green, a tube low in vacuum willshow a bluish green, while a medium tube will be an inter-mediate green. For dental radiography, a fairly high tube is indicatedand its vacuum should be kept as nearly uniform as pos-sible. This is ma
. Dental and oral radiography; a textbook for students and practitioners of dentistry . Fig. 25.—Diagram of an x-ray tube. The hemisphere in front of the target which is the activehemisphere, is evidenced by a green fluorescence, theshade of coloring depending upon the degree of vacuumof the tube. The fluorescence of a highly exhausted tubewill be a light yellowish green, a tube low in vacuum willshow a bluish green, while a medium tube will be an inter-mediate green. For dental radiography, a fairly high tube is indicatedand its vacuum should be kept as nearly uniform as pos-sible. This is made possible by utilizing the third ter-minal from the x-ray machine. By placing the spark gapof tliis terminal about three or four inches from the nega- 66 DENTAL AND ORAL RADIOGEAPHY tive terminal of the machine, the current will, when thevacuum of the tube gets high enough to resist its pas-sage, pass over the gap, down the third terminal wire. Fig. 26.—The coil or transformer tube. into the regulating chamber where by heating the as-bestos it will liberate gas and thereby reduce the vacuumof the tube. REQUISITES OF DENTAL X-IIAY LABORATORY 67 In addition to tlie general types of tubes already de-scribed, there are certain specialized forms of tubes which
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