. The principles and practice of roentgenological technique . all the x-rays enter-ing it, the method of measurement still has PHOTOGRAPHIC METHODS 105 practical value if but a constant fraction ofthe total is absorbed. The readings on theelectrometer must be compensated for by aconsideration of the ionization effect of thesecondary rays characteristic of the gas andthose arising from the walls of the metalchamber struck by the rays. The following methods are utilized for theestimation of x-ray quantity in medicine: 5. Photographic. The sensitive emulsion of a photographicplate is more respons
. The principles and practice of roentgenological technique . all the x-rays enter-ing it, the method of measurement still has PHOTOGRAPHIC METHODS 105 practical value if but a constant fraction ofthe total is absorbed. The readings on theelectrometer must be compensated for by aconsideration of the ionization effect of thesecondary rays characteristic of the gas andthose arising from the walls of the metalchamber struck by the rays. The following methods are utilized for theestimation of x-ray quantity in medicine: 5. Photographic. The sensitive emulsion of a photographicplate is more responsive to soft than to hardrays. The effects are also considerably in-creased if the particular ray is capable ofgenerating the characteristic rays of silver andbromine and thus the action on the emulsionis really not proportional to the actual ab-sorption. But as a comparative measurementthis photographic action is of value bearing inmind certain limitations. Areas of equal den-sity on the same plate indicate that equalamounts of energy were absorbed by these. Fig. 147.—A test similarly made with five milliam-peres, and a tube backing up four-inch centimeter ray was thus obtained. Thiswas absorbed 50% at the depth of I cm. andreduced to 25% at 2 cm., i2j/2% at 3 at 4 cm., at 5 cm. areas but this gives no idea of the total energyof the beam as it emerged from the tube. Quantity may be translated into electricalterms and measured by photographic the quantity of radiation reaching a cer- tain reacting surface may be said to be equal tOthe quotient of the product of current, voltagesquared and time divided by distance squared,,or I \- tD=the quotient being in arbitrary units. Aslong as the same quotient results from thevarying of the factors, the darkening of thejjlate will be the same if no object is inter-posed, but if the latter condition exists, thehigher voltage factor in one formula will beresponsible for a greater blackening of theplate.
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectradiogr, bookyear1920
