CHAPTER 9 



MASS SPECTROGRAPHS 



9.1. Aston Mass Spectrograph. An arrangement of electric and magnetic 

 fields devised and perfected by Aston [1,2] was the first employed for exten- 

 sive and accurate measurements of isotope masses and relative abundances. 

 A highly collimated ion beam emerging from the slits Si and So, as shown in 



Fig. 60. Aston mass spectrograph. 



Fig. 60, passes through a strong uniform electric field between two parallel 

 electrodes which deflects the ions by a small angle 



v m 



where / = length of path between plates 



V = deflecting voltage on plates 



v = initial ion velocity 



e = ion charge 

 m = ion mass 

 The defining vane F then permits only ions within a small prescribed range 

 of velocities to enter the uniform magnetic field H. The angular deflection 

 in the magnetic field is given by the expression 



<p == HI 



\lVmJ 



where L = length of path in magnetic field 



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