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at this temperature is 0.25 eV. It is believed that the
thermalization is part of the total slowing down pro-
cess since the region of epitermal neutron energy is
narrow such as 0.025 eV to 1 eV compared to total
range of neutron energies. Thermalization process if
likely the effect of chemical effects. In fact, cold neu-
trons also can be produced when the medium of neu-
tron is passes is cooled down to liquid nitrogen tem-
perature. Energy of neutron is much less than 0.025
eV, neutron in category is called cold neutron. In gen-
eral, thermal and cold neutron can be detected easily
compared with epithermal or fast neutrons. Further-
more, thermal and cold neutron become more useful
and they have many applications in scattering, imaging
and diffraction techniques.

1.6.3 Neutron Diffusion and absorption

Thermal neutron may diffuse in the materials at ther-
mal equilibrium state. The diffusion process happen
until either captured or escape from the vicinity of ma-
terial. The concentration of thermal neutron in the en-
vironment of fast neutron increases with the presence
of hydrogen element and also with the absence of ther-
mal neutrons absorbing materials. Therefore, reduc-
tion in diffusion capability is depending on the presense
of absorbing materials. Each material has neutron ab-
sorption probability characteristic, determined by ab-

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