HEALTH PHYSICS AND RADIATION PROTECTION 



87 



but does not appear destined to gain wide usage. A rutherford represents 

 that amount of radioactive material in which 10^ atoms disintegrate per 

 second. 



Units of Radiation Dose. It is necessary to have a unit to denote the 

 energy absorbed by material from the radiation that passes through it. 

 The roentgen, (r), named after the discoverer of X rays, has been formally 

 defined as that quantity of X or gamma radiation such that the associated 

 corpuscular emission per 0.001293 g of air produces, in air, ions carrying 



Table 3-1. Summary of Characteristics of Alpha, Beta, and 



Gamma Radiation 



one electrostatic unit of quantity of electricity of either sign. A smaller unit 

 is often used — miUiroentgen (mr) = 10~^ r. 



For practical purposes, it is necessary to understand the physical signif- 

 icance of the unit and its relationship to biological effects. The roentgen 

 represents a certain amount of energy absorbed in a certain amount of air. 

 If a beam of radiation passes through a layer of air, it will have a certain 

 intensity which represents all the energy that passes through. However, 

 only a fraction of this energy may be absorbed and is thus able to produce 

 the ionization that is measured in roentgens. Thus the roentgen does 

 not tell us how much radiation passed through the air but does give a 

 measure of how much was absorbed. For comparison, remember that the 



