156 



RADIATION BIOLOGY 



/ (In 



J = 



K 



L = 



clE 



JecIE 



KecIE 



(9) 



j dn 



j dn 



As the energy of the photon increases above a few miUion electron 

 volts, the range of the ejected electrons increases rapidly to distances 

 comparable to the mean free path of the incident photons. Thus at 

 5 Mev the range of the electron in air is about 7 per cent of the average 

 mean free path of a photon of equivalent energy, and at 50 Mev this 

 range increases to 34 per cent. Besides, at higher energies, secondary 

 electrons begin to lose some of their energy by radiative collisions with 

 nuclei, namely, by the creation of tertiary photons, and the ratio of the 

 first to the second types of energy loss is of the order of EZ/800, where E 

 is the electron energy in mega electron volts and Z is the atomic number of 

 the material traversed. These tertiary photons will produce de novo 

 other corpuscular radiation, mostly at considerable distance from the site 

 of primary interaction. 



Table 2-1. 



Correction Factors for Thimble Chambers 



[See Eq. (7)] 



