ABSTRACT
Neutrons may interact with matter in one or more of the following reactions:
1. Elastic scattering: (n,n) reaction: A neutron collides with the atomic nucleus and then loses its kinetic energy. It should be noted that the neutron loses less kinetic energy when it collides with a heavy nucleus. In contrast, it loses more kinetic energy when it collides with a light nucleus. Hydrogen (1H) is, therefore, the most eective neutron moderator because it is the lightest nucleus having a mass almost the same as a neutron. Elastic scattering is most important in the production of low energy or slow neutrons from fast neutrons emitted from the source for neutron radiography. Water, paran, and polyethylene are common neutron moderators. In fact, hydrogen-2 (2H, the so-called deuterium) is the best neutron moderator due to its extremely low neutron absorption probability. Heavy water (2H2O) has neutron absorption cross section only about 1/500 that of light water (1H2O), but heavy water is very costly.
