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LAUE SPOTS AND
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CRYSTAL ANALYSIS 207
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value of [! is called the crystal grating constant See, also,
Section 3—4.
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An 'X—ray spectrum, such as that in gure 9—12A, is obtained
With the apparatus of gure 9710 by varying the angle 6, keeping
the chamber at an angle 26. It is seen in this case, where tungsten
was used as the target and calcite Was used as the crystal, that the
_
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X—rays consisted of three “lines
”
or wave-lengths.' The distance
—
d was calculated from equation 1—25 and found to be 2.814 ang—
stroms.
The wave—lengths of the tungsten lines were calculated
from the Bragg law, using both the rst and second orders (n = 1
and 2).
The same values were found when the beam was reected
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