ABSTRACT
At the heart of neutron physics, reactor physics holds a special place because of its numerous practical applications. It permits us to determine not only the critical condition to which every reactor submitted, but also the distributions of neutron flux indispensable for evaluation of specific powers, burn up rates. The conception operational or projected reactors have necessitated highly advanced neutron studies as well as other investigations, both technological and economic. Neutron physics constitutes in some sense the bridge between the microscopic level and the macroscopic level. It distinguishes two sorts of media. Media which are passive or non-multiplying characterized the scattering cross sections s and capture cross sections c of the various isotopes of which they composed. Media which multiply contain at least one fissionable isotope. The totality macroscopic cross sections define the geometry of the problem treated and the distributions of neutron flux. If all the media are passive, it will introduce a neutron source somewhere in the system.
