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4.2.1 Collimator

Neutron from reactor core is classified a white neu-
tron beam, where the energy of neutron in the neutron
spectrum is a wide ranges. The intensity of neutron
from the core to the sample in diffraction device should
be maximised. Collimator is used to maintain thermal
neutron beam intensity and focuses to the targeted di-
rection. The path of neutron in the collimator will fulfill
the optical principle. For short distance of neutron path
and low cost, open parallel beam collimator is used, for
a slight high cost, soller collimator can be used. Soller
collimator usually used to collimate and focus neutron
after penetrating sample and detectors.

Furthermore, for large and high flux reactor, col-
limation of thermal neutron beam in neutron diffrac-
tometer is done using super mirror, known neutron guide.
Neutrons are let to fly within the two wall of neutron
guide which is made by super mirror. Neutron will scat-
ter and maintain inside the guide if the scattering angle
of incident neutron is smaller than critical angle of the
mirror. The mirror form inside the inner wall of guide is
made by titanium materials. This material has strong
compatibility with neutron and hard enough to prevent
damage due to neutron interactions.

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