Neutrons, capture reaction elastic scattering

Thru 1967, emphasis was given to the use of neutrons as the bombarding source of radiation. Almost all possible neutron reactions were considered including moderation of fast neutrons by hydrogen in the expl, thermal capture reactions, elastic and inelastic scattering of neutrons and neutron activation reactions. These neutron reactions are listed as follows ... 

For the present discussion, all the neutron-nucleus reactions defined above will be included under the general heading collision. Thus, when we talk about the probability of a nuclear collision, we imply any one of the four principal reactions capture, fission, elastic scattering, or inelastic scattering. 

Neutrons may collide with nuclei causing one of the following reactions inelastic scattering, elastic scattering, radiative capture, or fission. 

The shape resonances have been described by Feshbach in elastic scattering cross-section for the processes of neutron capture and nuclear fission [7] in the cloudy crystal ball model of nuclear reactions. These scattering theory is dealing with configuration interaction in multi-channel processes involving states with different spatial locations. Therefore these resonances can be called also Feshbach shape resonances. These resonances are a clear well established manifestation of the non locality of quantum mechanics and appear in many fields of physics and chemistry [8,192] such as the molecular association and dissociation processes. 

As noted, the introduction of an impurity atom was discussed previously, and atomic displacement is the result of (n,p) and (n,a) reactions and (n,y) reactions followed by radioactive decay. Thermal neutrons cannot produce atomic displacements directly, but they can do so indirectly as the result of radioactive capture (n,y) and other neutron reactions or elastic scattering. 

Thermal neutrons cannot produce displacements directly, but can indirectly as a result of radiative capture and other neutron reactions or elastic scattering. 

For bulk samples, elastic scattering of the neutrons before the capture reaction may also play an important role, lengthening the path of the neutrons inside the target. The energy distribution of the neutrons may also be modified by elastic scattering especially in the case of hydrogenous materials. 

Here, the subscript i denotes any one of the following nuclear reactions inelastic scattering radiative capture 2), fission Z/, and elastic scattering 2. The symbol S denotes an appropriate total" cross section for the fast neutrons it is defined by [cf. Eq. (2.50)]... 

Each possible type of reaction which a neutron may undergo with the nucleus is associated with a specific cross section. The most important cross sections are g, elastic scattering g i, inelastic scattering Gy, radiative capture Gf, fission (Tp, (n, p) reaction g, (n, a). 

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