. Radiography, X-ray therapeutics and radium therapy . Fia. 50.—Oscilloscope tube in action.(Schall.) a, The appearance of a tube with the run-cutpassing in the right direction with a traceof reverse current. //, The appearance with the current passingin both directions in almosl equal pro-portions. 54 RADIOGRAPHY Secondary Radiations, Cause, and Methods of Suppression.— Secondary rays are produced by the reverse current. All those X-rayswhich do not emanate from the focus of the anti-cathode are called secondaryrays. They have the same penetrating power as the primary rays and areplentiful in
. Radiography, X-ray therapeutics and radium therapy . Fia. 50.—Oscilloscope tube in action.(Schall.) a, The appearance of a tube with the run-cutpassing in the right direction with a traceof reverse current. //, The appearance with the current passingin both directions in almosl equal pro-portions. 54 RADIOGRAPHY Secondary Radiations, Cause, and Methods of Suppression.— Secondary rays are produced by the reverse current. All those X-rayswhich do not emanate from the focus of the anti-cathode are called secondaryrays. They have the same penetrating power as the primary rays and areplentiful in hard tubes, but they project the outlines of the objects in otherdirections than the primary rays, and a loss of sharpness results. When they are present it is necessary to do something to preventdeterioration of the negative. Secondary rays are also produced, or adiffusion of the primary rays takes place in the patients body. It is probable. D C B A A B C D Fig. 51.—Diagrams showing the paths taken by primary beams and secondary rays. (Schall.) that both of these manifest themselves during a long exposure. Fig. 51shows the path taken by the primary beam, and the manner of projection ofsecondary rays upon the photographic plate. The X-rays, A A, emanating from the focus of the anti-cathode projecta shadow, B B, of the object, 0, on the plate. If there were no secondaryrays this shadow would be of uniform darkness from B to B, and the space,BCD, would be free from any shadow. But if any current discharges inthe wrong direction, the so-called secondary rays are generated on the glassof the tube. They are indicated by the dotted lines b b. Although weakerin intensity, they project shadows, and in another direction than the primarynays will do; the shadows overlap, and the part between A B will not be so SUPPRESSION OF SECONDARY RADIATIONS 55 dark as that between A A and the space between B C will not be as clear asthat betw
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