38 BIOPHYSICALLY ACTIVE X-RAYS 



film of suitable size so that sample and echelon are in contact along their 

 long sides. The whole is exposed to the particular radiation against 

 which the operator wishes to protect himself. 



The developed photographic image then shows the relative trans- 

 parency of lead and protective material. The photographic density of 

 the image of this protective material is matched against the image of 

 one of the steps of the echelon. A sufficiently accurate estimate of 

 matched density can be obtained by direct observation. The lead 

 layer having the same photographic blackening as the unknown material 

 is chosen as representing its lead equivalent. 



Concrete as a protective material was investigated by Singer, Taylor, 

 and Charlton [1938], who found that the thickness of a concrete barrier 

 which will provide adequate protection at 400 kv is about 26.5 cm, and 

 the required thickness at 200 kv is 22 cm. 



The radiation due to scattering is often so widespread that the whole 

 room is filled with it, since it is emitted from floors, walls, table, attached 

 metal parts, and patient. This emission may be a source of great danger 

 in specific x-ray installations and apparatus. The best practice for 

 protection during radiographic and radiotherapeutic technique is un- 

 questionably to enclose the operator and controls in a booth protected 

 by lead or barium plaster. This protection cannot be obtained in 

 fluoroscopic work, and it is here that the most danger arises. A simple 

 test shows the possible extent to which the operator is exposed to x-radia- 

 tion. With patient placed upon an x-ray couch and with undercouch 

 tube box, a fluorescent screen between patient and operator at right 

 angles to the couch top will be found to be brightly illuminated if scatter- 

 ing danger exists. It is very probable that under these circumstances 

 the usual lead equivalent of the operator's apron is insufficient protec- 

 tion. For proper protection 1.5 mm lead equivalent is recommended. 



It has been suggested that, since the region of the operator so radiated 

 is that of the hypochondrium, it is very probable that the overfrequent 

 occurrence of duodenal ulcer in radiologists may be attributed to the 

 direct effect of radiation upon the mucosa of the duodenum, resulting 

 at first in a generalized inflammation and later in definite ulceration. 



The United States Department of Commerce, National Bureau of 

 Standards, issues a handbook HB 20, " Protection from X-Rays," price 

 10 cents, containing the recommendations of a committee representing 

 the International Safety Committee and National Bureau of Standards. 



Ionization of a Gas by X-Radiation 



Since, in therapeutic work, speed and comparative ease of operation 

 are essential, ionization measurements are being used as the most direct 



