56 



RADIATION BIOLOGY 



Similarly, the relative frequency of ionizing collisions in which the electron escapes 

 with an energy between E and E -\- 8E can be indicated as giiE) 8E. Then 



9li(^) dE = ?fligiiE) 6E = Nt 



mv^ El 



(23) 



Figure 1-38 shows sample data on the coefficients g and on their slow depend- 

 ence on the energy of the incident particle. These coefficients can be estimated 



Q 



b5 



UJ 

 CD 



>- 

 O 



q: 



UJ 





10 



20 



ia) 



o 



UJ 



o 



o 



UJ 



U- 



o 



o 0.0001 



o 



2 0.00001 



0,000001 



100- kev 

 INCIDENT ELECTRON 



ALL COLLISIONS 

 KNOCK -ON ONLY 



5 10 20 



50 



500 1000 



100 200 

 (b) 

 ENERGY OF EJECTED ELECTRON, ev 



Fig. 1-38. Fraction of inelastic collisions of fast electrons against hydrogen atoms 

 which lead to various energy absorptions. The curves represent the coefficient 

 gi{E) of Eq. (23). The areas in the rectangular blocks represent the values of gri of 

 Eq. (22) pertaining to the excitation to the first excited level and to all other levels 

 combined. {Courtesy M. Lewis.) 



fairly readily from data on absorption spectra, relying on the similarity of the 

 action of glancing collisions and of electromagnetic radiation and on a sharp 

 subdivision of collisions into glancing and knock-on ones. 



