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Figure1.2.
First X-ray spectroscope used by Moseley in 1913. (a) X-ray tube with T
=
metal target
that can be exchanged; S
=
slit; W
=
window; goniometer with B
=
base for the crystal; P
=
photo-
graphic film. (b) A metal cylinder in front of an X-ray tube. The cylinder with slit and rotating
crystal in its center can be evacuated. Figure from Ref. [3], reproduced with permission from
Taylor & Francis.
metallic cylinder. The Braggs explained the diffraction of X-rays at the three-
dimensional crystal as their reflection at parallel planes of the crystal lattice and
determined the wavelength of the X-radiation according to the law later called
Bragg's law. Furthermore, the interplanar distance of different other crystals
had been determined. Then, in 1913, Moseley established the basis of X-ray
fluorescence analysis by replacing the Mo anode by several other metal plates.
He found his well-known law [3], which relates the reciprocal wavelength 1/
λ
of
the“characteristic”X-rays to the atomic number
Z
of the elements causing this
radiation. Moseley probably missed a Nobel Prize because he was killed during
World War I at the Dardanelles near Gallipoli when he was just 28 years old
(Figure 1.3b).
In 1904, Barkla had already discovered the polarization of X-rays, which is a
hint to their wavelike nature [5]. Ten years later, he bombarded metals with
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