828 HANDBOOK OF PHOTOGRAPHY 



Industrial X-ray Technique. — In making an industrial radiograph the factors to be 

 considered are (1) thickness and composition of object under examination, and (2) 

 size and shape of the object. There are, naturally, many other influencing factors, but 

 they are mostly small mechanical problems which vary from one piece of work to 

 another and can be solved with a little ingenuity. 



1. Thickness and composition of the object determine the voltage, current, and 

 time to be used in making an exposure. In the majority of cases voltage and time 

 are the only factors changed, and the current remains at some predetermined setting; 

 say 5 ma. Many curves have been published to give the proper settings for penetra- 

 tion of "steel," but they are notably unreliable and inaccurate. "Steel " has become a 

 loose, generic term which no longer denotes any specific metal with fixed chemical and 

 metallui'gical properties, and it covers a wide range of alloys. Variations in metal 

 densities, atomic properties. X-ray machine calibration, development technique, etc., 

 involve such large exposure differences that it is far better for each individual operator 

 to establish his own exposure charts by the trial-and-error method. After a number of 

 exposures on different alloys, the technician will develop a sense of exposure technique 

 which can then be enhanced by reference to a table of element and alloy densities. 



Table II. — Specific Gravity op Metals Encountered in Radiography 



Metal Specific Gravity 



Iron (99.94 Fe) 7 . 86 



Iron, cast (94 Fe, 3.5 C, 2.5 SiJ 7 . 00 



Stainless steels (90 Fe, 8 Cr, 0.4 Mn, 0.1 C) 7 . 75 



Alleghany metal (Fe, 18 Cr, 8 Ni, Mn, Si,^ C) 7.86-7.95 



Copper (99.9 Cu) '. 8.50 



Brass, ordinary (67 Cu, 33 Zn) 8.40 



Aluminum (99.2 Al) 2.71 



Nickel (99.5 Ni) ■ 8. 86 



Nichrome (80 Ni, 20 Cr) 8.50 



Monel metal (60 Ni, 33 Cu, 6.5 Fe) 8 . 90 



Lead (93 Pb, 7 Sb) 11.00 



Gold, standard Gt. Br. (92 Au, 8 Cu) 17. 17 



Platinum (90 Pt, 10 Ir) 21 . 61 



Tungsten ; 14 . 00 



A few of the metals frequently encountered in industrial X-ray work are given in 

 Table II with their composition and specific gravities. The higher the relative 

 gravities are, the higher the X-ray voltage must be to penetrate the metal. Gravities 



depends on the type of cone available. In any instance, the best results will be obtained when the small- 

 est possible cone is used, according to the area to be covered. 



"The procedure changes with the size of cone used. The smaller the cone, the greater the energy 

 required, and the larger the cone the less energy required. However, the improved contrast made 

 possible by the smaller cone, despite the increase in energy necessary, makes its use advisable whenever 

 possible, either with or without the Bucky diaphragm. 



" To change the radiographic density for any area, the best results will be obtained if only one factor 

 at a time is changed. The two factors which may be considered variable are voltage and exposure time. 

 Of these two, voltage is the variable factor of preference. 



" To change a Potter-Bucky procedure to one without the diaphragm, either deduct approximately 

 15 kv. or use J-i the exposure time as given on the chart for Potter-Bucky work. To reverse the 

 procedure, either add 15 kv.p. or use 4 times the exposure time. 



"Immobilization of the part should always be provided when practical; sand bags for such parts as 

 extremities, and immobilizing bands for the skull, pelvis, spine, etc.; cones or cylinders for sinuses. 



"y-z mm. to 1 mm. of aluminum should be used as a filter, with the following exceptions: soft tissue 

 technic in extremity work; radiography without screens; chest. 



"For children from 5 to 12 years of age, either a reduction in penetration of approximately 10 kv.p., 

 or 3-2 the exposure time given on the chart, should be made. 



"One star * indicates that the patient should stop breathing. 



"Two stars ** indicate that the patient should take a full breath and hold it." 



