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BELL SYSTEM TECHNICAL JOURNAL 



increasing grain size of the abrasive with which the surface of the plate was 

 lapped. 



2.1 The Single Crystal Spectrometer 



The single crystal spectrometer is used for X-ray measurement of 

 the orientation of quartz oscillator plates. In this instrument slit-coUimated 

 X-rays are reflected from a crystal into an ionization chamber and the rela- 

 tive intensity of the reflected X-rays is read from a meter showing the 



Rhfi, 



Rha, 



0.5 0.6 ^ 0.7 



WAVELENGTH IN ANGSTROMS 



Fig. 1. — X-Ray spectra from a rhodium target at 23 and 40 kilovolts. 

 purity present. (Adapted from Siegbahn, Spectroscopy of X-Rays). 



Ruthenium im- 



amplified current resulting from the ionization of the gas in the chamber by 

 the X-rays. Since the reflected white radiation is too weak to cause a meas- 

 urable amount of ionization, only the reflected characteristic radiation is 

 measured by the ionization chamber. For most purposes a copper-target 

 tube is used and the /3 radiation (comparable to Rh^ of Fig. 1) is eliminated by 

 a selective filter so that only the a radiation is used, the X-rays thus being 

 essentially "monochromatic". 



Three different techniques for examining surface layers of crystals with 

 the single crystal spectrometer will be described. Two of these employ 



