Mechanism of Energy Loss by Scattering Collisions

The elastic-scattering process, however, suffers no such restriction. Regardless of the energy of the incident neutron, an elastic-scattering collision can cause some reduction in the neutron energy. The extent 

1 Nuclear energy levels (a) low mass number (5) high mass number. 

In this treatment we examine the nuclear reactor with the aid of an infinite- medium model which describes the neutron-density distributions in terms of the kinetic energy of the neutrons. This model is the immediate extension of the one-velocity approximation introduced in Chap. 3. In the present analysis we discard the one-velocity restriction and attempt to describe the trajectory of the neutron in energy space as it is slowed down by elastic-scattering collisions with the nuclei of the medium. In 

Because of the assumption of isotropy of medium and source emission, the number of neutrons moving in a given direction per unit solid angle per unit volume will be the same for all directions. Thus for systems at steady state, the energy distribution alone will suffice to describe the neutron population. Consequently, for this calculation, we can use the functions for the neutron density and flux given by (3.49) 

The material of the infinite medium is characterized by neutron cross sections Sa( ), 2,(J ), and / E)y and v is the average number of neutrons per fission. We define 

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