XV. ELECTRONS, NEUTRONS, AND ALPHA PARTICLES 



527 



therapeutic use of this radiation. Applying the formula given in 

 Section CI, it will be seen that only extremely small proton currents 

 are needed in order to deliver doses of a few thousand roentgens. 

 If, in a 2-A m.e.v. proton accelerator, 20 na. of protons were focused 

 onto an area of 1 cm.^, and 10% of these emerged through a thin 

 window, the remainder being absorbed in the supporting grid, the 



> 



ai 



o 1400 



Q. 



=> 1200 



UJ 

 CJ 



q: 



UJ 



z 1000 



o 



ll. 



UJ 

 if) 



u. 

 o 



U) 



H 

 O 

 CC 



o 



e) 



< 

 ac 



800 



600 



400 



200 





 



Fig. 



2 

 20 



4 

 40 



6 

 60 



8 

 80 



10 

 100 



120 



140 



160 



PROTON ENERGIES, m.e.v. 



13. Curves showing ranges in tissue of protons having 

 energies 0-10 and 0-150 m.e.v. 



16 



> 



o 



CD 

 < 



12 (O 



UJ 



o 

 q: 



10 S 



cr 

 o 



3 



O 

 UJ 



4 ^ 



UJ 



o 

 2 ^ 



UJ 



o 



< 

 cr 



mean dose rate beneath the window would be 2 to 3 X 10^ r. per 

 second. The total penetrating power of the protons would be 70- 

 230 \i of tissue according to the energy, some of which would, of 

 course, be lost in the window. Ordinary cyclotrons commonly oper- 

 ate with mean proton currents of the order of 10 jua. and much larger 

 currents may be obtained. The mode of operation of the cyclotron 

 is such that the radiation varies somewhat in intensity with the 

 periodicity of the radiofrequency supply. This intensity variation is 



