236 



BIOLOGICAL EFFECTS OF IONIZING RADIATIONS 



and appreciated, especially by medical people. The three most important 

 facts are: (1) Living tissue is killed. (2) Mutations, which may lead to 

 cancer or to progeny which cannot live in the environment, can occur. 

 (3) The central nervous system can become hypersensitized; and this could 

 lead to a whole host of nervous and "somatopsychic" disorders. Radiolo- 

 gists understand much about (1); something, but really far too little, about 

 (2); and at this date have only an inkling about (3). 



Figure 9-2. Man's Environment of Radiations. Normal background of ionizing radia- 

 tions varies widely in the range 0.7 to 0.4 roentgens/yr, depending upon his location, 

 natural shielding in his home, etc. Anything above 0.3 r/week is currently considered 

 "dangerous." 



DOSIMETRY 



Dose Units 



From the point of view of effect, the most important quantity is the rather 

 empirical one — the rem (roentgen equivalent man). One rem is defined as 

 that amount of damage to tissue caused by radiation of any type which pro- 

 duces the same biological effect as does 100 ergs absorbed per gram of tissue 

 from incident X or gamma radiation. Since one rad (radiation absorbed 

 dose) is defined as that amount of X or gamma radiation which, when ab- 

 sorbed, adds 100 ergs per gram (i.e., 6.24 x 10 13 ev/g) to the energy of the 

 tissue, one rem of damage is produced by 1 rad of absorbed X or gamma 

 radiation. 



