Sec. 9.4] 



MA SS SPECTROGRAPHS 



283 



V = 2F log- 2 



volts 



where V = ion accelerating voltage at source 



r\ = radius of inner electrode 



r 2 = radius of outer electrode 

 The axial distance a from edge of the magnetic field where the ions enter 

 to the point of focus (see Fig. 63) is given by 



a = iW 



2mV 



cm 



where H = magnetic field strength 

 m = mass of particle 

 e = charge of particle 

 c = velocity of light 

 All masses are focused on a plane making a 45-deg angle with the axis 

 at the entrance point of the magnetic field. The distance of the focal point 



Fig. 63. Mattauch double-focusing mass spectrograph. [J. Mattauch and R. Herzog, 

 Phys. Rev., 50, 617 (1936).] 



along this plane for a particular value of m/e is then 



at 2 fiiVo 



cm 



Hence, the mass scale varies as \/m and can be readily established from 

 accurately known masses. 



The dispersion, assuming e to be constant, is given by 



db_ 1 I 



dm ~'~~ H\j, 



em 



