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preface to fifteenth edition

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SPECTROSCOPY 7.13<br />

Emission<br />

line K 1 K 2 K 1 K 2 L 1 L 2 L 1 L 2 L 1<br />

Relative<br />

intensity 500 250 80–150 5 100 10 30 60 40<br />

For angles at which the K 1 , K 2 doublet is not resolved, a mean wavelength [K¯ (2K 1 <br />

K 2 )/3] can be used.<br />

Filters. The K spectra of the light metals, often used as target material in the production of X-<br />

rays for diffraction studies, contain three strong lines, 1 , 2 and 1 , of which the lines form a<br />

doublet with a narrow wavelength separation. The K radiation can be eliminated by using a thin<br />

foil filter, usually of the element of next lower a<strong>to</strong>mic number <strong>to</strong> that of the target element: the K<br />

lines are transmitted with a relatively small loss of intensity. Table 7.5, restricted <strong>to</strong> the K wavelengths<br />

of target elements in common use, lists the calculated thicknesses of filters required <strong>to</strong><br />

reduce the K 1 /K 1 integrated intensity ratio <strong>to</strong> 1⁄100.<br />

Interplanar Spacings. Diffrac<strong>to</strong>meter alignment procedures require the use of a well-prepared<br />

polycrystalline specimen. Two standard samples found <strong>to</strong> be suitable are silicon and -quartz (including<br />

Novaculite). The 2 values of several of the most intense reflections for these materials are<br />

listed in Table 7.6 (Tables of Interplanar Spacings d vs. Diffraction Angle 2 for Selected Targets,<br />

Picker Nuclear, White Plains, N.Y., 1966). To convert <strong>to</strong> d for K¯ or<strong>to</strong>d for K 2 , multiply the<br />

tabulated d value (Table 7.6) for K 1 by the fac<strong>to</strong>r given below:<br />

Element K¯ K 2<br />

W 1.007 69 1.023 07<br />

Ag 1.00263 1.007 89<br />

Mo 1.00202 1.006 04<br />

Cu 1.000 821.00248<br />

Ni 1.000 77 1.00232<br />

Co 1.000 721.00216<br />

Fe 1.000 67 1.00204<br />

Cr 1.000 57 1.001 70<br />

Analyzing Crystals. The range of wavelengths usable with various analyzing crystals are governed<br />

by the d spacings of the crystal planes and by the geometric limits <strong>to</strong> which the goniometer<br />

can be rotated. The d value should be small enough <strong>to</strong> make the angle 2 greater than approximately<br />

10 or 15 deg, even at the shortest wavelength used: otherwise excessively long analyzing crystals<br />

would be needed <strong>to</strong> prevent the direct fluorescent beam from entering the detec<strong>to</strong>r. A small d value<br />

is also favorable for producing a large dispersion of the spectrum <strong>to</strong> give good separation of adjacent<br />

lines. On the other hand, a small d value imposes an upper limit <strong>to</strong> the range of wavelengths that<br />

can be analyzed. Actually the goniometer is limited mechanically <strong>to</strong> about 150 deg for a 2 value.<br />

A final requirement is the reflection efficiency and minimization of higher-order reflections. Table<br />

7.7 gives a list of crystals commonly used for X-ray spectroscopy.

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