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4.2.2 Monochromator
Monochromator is consisted of single crystalline ma-
terials, mostly made by Silicon, High Pyrolitic Germa-
nium (HPGE) or other materials. The monochromator
are designed according to the specific crystal lattice ar-
rangement, for example [110], [111] and etc. The neu-
tron at a specific energy or wavelength will be scattered
according to the Bragg Law given in Equation 4.1.
nλ = 2dsin(θ) (4.1)
where, d is spacing in between two crystal planes of
single crystal and λ is wavelength of incident neutron
on the particular crystal plane. The angle θ half of
take-off angle of incident neutron beam with the crys-
tal plane of monochromator gives the highest neutron
peaks. Each monochromator has critical angle which
responsible to provide the highest reflected neutron
beam to shine the sample.
Neutron diffractometer at low flux research nuclear
reactor usually has single monochromator as compared
with double monochromator for diffractometer in high
flux nuclear research reactor. Double monochroma-
tor is suitable for large and high flux thermal neutron.
Neutron beam from monochromator is used to irradi-
ate and interact with the sample. Since the size of neu-
tron beam after monochromator, the size is reduce by
placing the aperture slit.
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