286 



JSOTOPIC TRACERS AND NUCLEAR RADIATIONS 



[Chap. 9 



the electrostatic analyzer and the accelerating voltage for any ion that 

 traverses the central path between the plates is expressed by 



V e = 2F log 





where V e = analyzer voltage 



V ' o = accelerating voltage or energy of ion in central path 



r\ = radius of inner condenser plate 



ri = radius of outer condenser plate 

 In traversing the electrostatic analyzer, ions of energy V, differing slightly 

 from V , are focused into an energy spectrum in the focal plane of the analyzer 



5^~\" 



Fig. 65. Bainbridge-Jordan double-focusing mass spectrograph. [A'. T. Bainbridgc and 

 E. B. Jordan, Phys. Rev., 50, 282 (1936).] 



and again diverge before entering the magnetic field. The linear displace- 

 ment of an ion from the central path in the focal plane of the analyzer for 

 an ion of energy V, to a close approximation, is given by 



d = 2R e B 



where R e = radius of central path through electrostatic analyzer and 



V - V 



B = 



V 



Only those ions in the central path with a particular value of m /e are 

 deflected by the magnetic field through exactly 60 deg when the magnetic 

 field satisfies the relation 



H 



R m \ 



2m„V n 



where R m = radius of curvature for the ion m /e traversing the central path 



through the magnetic field 

 Under these conditions the ion enters and leaves normal to the edge of the 

 magnetic field, and ions of the same m /e but with different energies are 



