. The principles and practice of roentgenological technique . o a point is secured by thedesign of a concave cathode as already indi-cated. Aluminum is commonly utilized, as a cath-ode because it does not disintegrate, emits elec-trons with ease and has high heat conductivity. By diminishing the size of the cathodal elec-trode, the penetration of the resulting x-raysis increased. X^arrowing the space betweenthe cathode and the glass wall and withdraw-ing the cathode into the cylindrical glass ex-tension in which it is placed have the sameefifect. In the electron tube the concentration of theca
. The principles and practice of roentgenological technique . o a point is secured by thedesign of a concave cathode as already indi-cated. Aluminum is commonly utilized, as a cath-ode because it does not disintegrate, emits elec-trons with ease and has high heat conductivity. By diminishing the size of the cathodal elec-trode, the penetration of the resulting x-raysis increased. X^arrowing the space betweenthe cathode and the glass wall and withdraw-ing the cathode into the cylindrical glass ex-tension in which it is placed have the sameefifect. In the electron tube the concentration of thecathode stream is secured by an electrostaticfield produced by means of the molybdenumcollar. (4) The velocity change of the cathodestream is produced by a barrier of metal(tungsten, platinum or iridium) which con-stitutes the anode or target of the tube. [80] The intensity of the resulting radiatio* de-pends on the constitution of the target. If theintensity of radiation of platinum is con-sidered to be 100, tungsten is 91, molybdenumis 50, and nickel is Fig. 96.—The distribution of x-rays in the activehemisphere. The intensity reaches its maxi-mum in a direction about 60° from the normal(6). The fall in intensity from 60° to 50° isvery marked. Actually the ra3rs are given ofiffrom the back of the target as well as the front. From the target the x-rays radiate in all di-rections in straight lines through an arc of onehundred and eightv degrees. The rays are not,however, evenly distributed upon all surfacesof the hemisphere of the bulb. The mostintense radiations are about the central bundleand at an angle of thirty degrees to the cathodestream at the point of impact upon the target. An x-ray tube correctly activated and freefrom inverse is separated b_v the anti-cathode, into two sharply defined hemispheres,the active half, in front of this target, fluor-escing a light green, while the inactive onebehind is relatively dark. In a correctly ener-gized tube the zones are
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