. Radiography, x-ray therapeutics and radium therapy . s contained therein,which is considerable, can be utilised. In order to obtain good pictures it is generally necessary to regulatethe hardness of a tube each time previous to using it, and the tube shouldbe adjusted for a medium hardness; and this should be done by meansof the regenerator. Suppression of Reverse (Inverse) Current The reverse current is obviously a great inconvenience and must be gotrid of if good negatives are to be obtained. It is possible to keep it downto a minimum by using a low voltage, a high self-induction, and a lo
. Radiography, x-ray therapeutics and radium therapy . s contained therein,which is considerable, can be utilised. In order to obtain good pictures it is generally necessary to regulatethe hardness of a tube each time previous to using it, and the tube shouldbe adjusted for a medium hardness; and this should be done by meansof the regenerator. Suppression of Reverse (Inverse) Current The reverse current is obviously a great inconvenience and must be gotrid of if good negatives are to be obtained. It is possible to keep it downto a minimum by using a low voltage, a high self-induction, and a lowfrequency in the primary coil, but if intense discharges are required we cannotsuppress it entirely in this way, and other means must be adopted. Valve tubes or spark-gaps are frequently connected in series with theX-ray tubes. In a Spark-gap the current can discharge easily between a point and aplate if the point is the positive pole, but it does not do so if the point isthe negative pole. It is possible, then, to create an impediment or resistance. Fig. 43.—Spark-gap. (Siemens.) to the cm-rent in one direction only, whereas the passage is left free inthe other. There are many types of Valve tubes, the most commonly used beingthe single valve tube, but the triple valve tube is also used. The nature of reverse current has already been explained. In allcoil outfits this has to be checked. It is possible by a careful adjustmentof primary current, interrupter, and tube, to cut this down to a minimum,but the slightest disturbance of these factors gives rise at once to a percentageof inverse current, which, if allowed to remain, has a deleterious efiect uponthe tube and tends to harden it. Should it become very hard the persistenceof inverse current with strong currents in the primary leads to damage ofthe tube ; sparking takes place, and the tube is punctured. It is generally appreciated that the current which is utilised in the pro-duction of X-rays is that which is passing whe
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