Relative Efficiency of Roentgen Ray Tubes. ioi 



radiated and also living animals (pigeons). Test strips of photo- 

 graphic paper (Kienboeck strips) were placed on the surface of the 

 radiated piece and at various depth of tissue. Pieces of meat were 

 used I, I2, 2, 3 and 4 inches in thickness. The very soft rays, which 

 usually act only on the surface of the skin of the animal and are 

 not selective but caustic in their action were absorbed by a plate 

 of aluminum 3 mm. thick placed between the tube and the tissue. 

 The pigeons were placed in a box 4 inches deep. One Kienboeck 

 strip was placed over the box and the other under the box. The 

 results of numerous experiments may be summarized as follows: 

 It takes about ^ of the time to obtain the same quantity of 

 rays on the surface with a Coolidge tube as compared with the old 

 type tubes. At the depth of 2 inches of meat the strip shows about 

 ■| of the quantity of the rays shown by the surface strip during the 

 same experiment with an old type tube and about \ by the Coolidge 

 tube. At a depth of 4 inches there is usually about \ of the quantity 

 shown on the surface obtained from a tube of the old type, while 

 from a Coolidge tube one obtains at the same depth usually about 

 \ of the quantity shown on the surface. There is no complete 

 regularity in the results of the experiments with either tube, but 

 the Coolidge tube shows a far greater uniformity. The reason for 

 this difference in the results is probably due to the following: the 

 Roentgen rays emitted by a tube are never uniform in their 

 character and represent all grades of hardness. The methods of 

 measuring the penetration of the tube reveal only the hardest 

 rays. Apparently the rays are more uniform in the Coolidge 

 tube and therefore a greater fraction of those entering the surface 

 reach a certain depth. This feature makes the tube more advan- 

 tageous than those of the old types. On the other hand it must 

 not be presumed that the rays of the Coolidge tube are greatly 

 superior in their absolute capacity of penetration. As stated above 

 the velocity of the kathode rays and the consequent penetration 

 of the Roentgen rays is in direct proportion to the intensity of the 

 high potential current. The latter can not be increased beyond a 

 certain limit in the Coolidge tube as it is constructed today. 



