. Radiography, X-ray therapeutics and radium therapy . result we desire to obtain. Using20 mgrms. of a radium salt of 500,000 activity on an applicator 2 , a marked reaction may be produced on the skin by one hours ex-posure. (A thin sheet of rubber or gutta-percha tissue should always beused to protect the radium.) A half mm. of aluminium acting as a screenwill delay the appearance of the reaction ; therefore, to get a similar degreeof reaction the exposure would require to be longer. When the activity ofthe radium is greater the effect will be proportionately increased. The metallic
. Radiography, X-ray therapeutics and radium therapy . result we desire to obtain. Using20 mgrms. of a radium salt of 500,000 activity on an applicator 2 , a marked reaction may be produced on the skin by one hours ex-posure. (A thin sheet of rubber or gutta-percha tissue should always beused to protect the radium.) A half mm. of aluminium acting as a screenwill delay the appearance of the reaction ; therefore, to get a similar degreeof reaction the exposure would require to be longer. When the activity ofthe radium is greater the effect will be proportionately increased. The metallic tubes containing free radium require to be used with screensof known thickness, which may be larger tubes of silver or platinum, of athickness of one to two millimetres of platinum or two to four mm. of these tubes are not available an efficient filter may be made by FILTRATION OF RADIUM RAYS 351 rolling a portion of sheet lead around the platinum tube containing theradium. Silver and lead have equal powers of obstructing the passage of. Fig. 231.—Flatmetal applica-tor. Railium ispacked in arearepresented bydotted lilies. Fig. 232.—-Showing method of arrang-ing tubes with filters. A thick silver screen with grooves totake two radium tubes. In front is agroove for platinum niters. Ten ofthese may be used ; each is T\; The holder has a thick backingof 1 cm. silver, to protect the adjacentskin surface from the rays when in use. Fig. 233. — Silverscreen 1 mm. thickadapted to containtwo tubes side byside and fittedwith screw ter-minal. the rays from the radium, platinum possessing twice theabsorption value of lead or silver. The thickness of the filter to beemployed is estimated beforehandaccording to the effect desired, thequantity of the radium employed,and the tissues to be treated. Secondary Radiations from Tubescontaining Radium.—It is not suffi-cient simply to use a filter for theabsorption of the radium rays. Itmust be borne in mind that thefilt
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