CHAPTER III 



The Use of X-Rays for Determining the Orientation 

 of Quartz Crystals 



By W. L. BOND And E. J. ARMSTRONG 



THIS paper is one of a series by the Crystal Research Group on the 

 manufacture of cjuartz oscillator plates. Certain sections of it which 

 are not original, but rather adaptations of text book material to the present 

 problem, are included for purposes of completeness and for the convenience 

 of those readers whose knowledge of the crystallographic literature may 

 be limited. 



3.1 Production of X-Rays for Quartz Crystal X-Ray Work 



X-rays are produced when electrons strike a metal target at high velocity. 

 The wave-length of X-rays given off from an X-ray tube varies from the 

 longest which can pass through the X-ray tube window to the shortest that 

 can be produced from the given target by the applied peak voltage. By 

 analogy to the visible spectrum this is referred to as "white" radiation. 

 For each different metal, however, there are characteristic radiations of 

 certain wave-lengths whose intensity markedly exceeds those of other wave- 

 lengths (Fig. 3.1). The strongest of these characteristic radiations is known 

 as the Kai, the next strongest (generally half as strong and of slightly longer 

 wave-length) as Ka^ and the third strongest (shorter in wave-length than 

 Kai) is A'|3. The higher the atomic number of the target, the shorter will 

 be the wave-length of the characteristic radiation. Therefore higher volt- 

 ages will be required to excite the characteristic radiation from the heavier 

 metals. (The minimum wave-length of X-rays that can be excited by any 



1.234 X 10~'* 

 given voltage is given by the equation Xmin. = :^ where V is 



expressed in volts and Xmin. in Angstrom units). 



Higher voltages also raise the intensity of the white radiation and, at 

 any given voltage, the white radiation produced from a heavy metal target 

 is more intense than that produced from a lighter metal target (see Figure 

 3.1). When "white" radiation is desired, as in Laue photography, heavy 

 metal targets, such as tungsten, are used: when "monochromatic" radiation 

 is desired, as in crystal goniometry, the lighter metal targets, such as copper, 

 are used because, with a lighter metal target (wave-length of char- 

 acteristic radiation long) the voltage, and therefore the intensity of the 



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