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# X-Ray Diffraction

الكلية كلية التربية للعلوم الصرفة     القسم قسم الفيزياء     المرحلة 3
أستاذ المادة فؤاد عطية مجيد       14/12/2016 10:13:36
A plane of atoms in a crystal, also called a Bragg plane, reflects X-ray
radiation in exactly the same manner that light is reflected from a plane
mirror, as shown in Fig.6.4.

Reflection from successive planes can interfere constructively if the path
difference between two rays is equal to an integral number of wavelengths.
This statement is called Bragg’s law.
Where in practice, it is normal to assume first order diffraction so that n = 1.
A given set of atomic planes gives rise a reflection at one angle, seen as a spot
or a ring in a diffraction pattern also called a diffractogram.
6.7 Moseley’s Experiment

The high intensity penetrating radiation emitted by X-ray tubes,
characteristic of the metal from which the target anode is made, was first
discovered by Barkla. He found that when the tubes were operated at higher
potentials, series of high intensity peaks, each of a specific wavelength, were
superimposed on the spectrum of the continuous bremstrahlung radiation
(Fig. 6.5).
The phenomenon is analogous to the atomic line spectra Seen in the visual
region of the electromagnetic spectrum. Changing the metal or element from
which the target anode in the X-ray tube is made alters the wavelengths at
which the high intensity peaks occur. The most penetrating series in an
element’s characteristic X-ray spectrum is called the K series; the second is
called the L series; the third the M series and so on.
Moseley carried out a systematic examination of the characteristic
radiation of as many elements as possible. He examined the X-ray spectra of
the 38 elements from aluminum (Al) to gold (Au). As regards 15 of these
elements, he studied just the K series; regarding another 17, just the L series;
as to the remaining 6 elements, both series. He recorded the spectra on
photographic plates.
Moseley discovered the following simple empirical relationship,
illustrated in (Fig 6.6), between the frequencies, (n) of the lines in each series
and the ordinal number, N, of the element’s position in the periodic table
(starting from hydrogen):

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