Protective Methods in Radiology 275 



On the other hand, the ratio of X-ray energy to gamma-ray 

 energy shows much smaller variations, the average value being 

 about 1.5. Clearly, further experiments will have to be made 

 before a tolerance dose for neutrons can be established. 



Reference is made in Smyth's report on Atomic Energy, "^^ 

 to the fact that the National Defense Research Committee of 

 the United States set up a health group, one of whose tasks 

 was to carry out research on the effects of radiations on persons 

 engaged in the operations associated with the atomic pile. The 

 results of the investigations of the group have not yet been 

 announced, but doubtless the knowledge of radiation effects will 

 have been greatly increased. 



Elaboration of Protective Sclieines 



When the tolerance dose for a particular type of radiation, 

 say, X-radiation, has been established and is measurable in terms 

 of a physical unit, the subsequent procedure in determining the 

 protection in any instance is to measure the dosage rate of the 

 radiation received at a specified point in terms of the unit 

 adopted, to determine the transmission values of the radiation 

 through various thicknesses of various absorbing materials, and 

 finally to calculate the thickness of the chosen absorbent which 

 is required to reduce the transmitted radiation received at the 

 point in question to the tolerance dosage rate. 



It is well known that X-rays and radium gamma rays are 

 absorbed more effectively by lead than by any other common 

 material. Hence lead or lead-impregnated materials, such as 

 rubber and glass, have generally been used to secure protection. 

 It is also customary to express the required protection in terms 

 of lead and to determine the "lead-equivalents" of other ab- 

 sorbents. 



When using X-ray equipment, steps must be taken to safe- 

 guard the operator against three types of radiation. In the first 

 place, the tube itself must be protected in all directions other 

 than that of the useful beam. Secondly, if the direct beam is 

 pointed at the operator, as is often the case in screening a 



