Diffracted
X-rays appear as circles of bright points around
the central beam
5.
Von Laue's Crystals
The spacing of slits in a diffraction grating
has to be comparable to the wavelength of the waves
being diffracted. Von Laue realised that a crystal could
be used as a diffraction grating for X-rays. In 1850
Bravais had suggested that a crystal is arranged as
a lattice, and the distance between molecules in a solid
is around a tenth of a nanometre. If the X-rays were
a wave the atoms in a crystal should cause them to diffract.
X-rays
were allowed into a lead box containing a crystal, with
sensitive film behind and to the sides. When the films
were developed there was a large central point from
the incident X-rays, but also many smaller points in
a regular pattern. These could only be due to the diffraction
of the incident beam and the interference of many beams.
Von
Laue published his discovery in 1912, more than ten
years after the discovery of X-rays. By using a crystal
as a diffraction grating, von Laue had proved the X-rays
were not particles, but waves of light with very small
wavelengths.
