Correction for Absorbing Medium

The thermal neutron distribution will be changed from the pure Maxwellian due to neutron absorption in the medium. The work of Con-veyou. Bate and 0sbom7 has been useful in this respect. Using a Monte-Carlo technique, they computed thermal neutron spectra for an infinite capturing medium. The calculations were carried out for a uniform medium of unbound nuclei of constant scattering cross section and l/v absorption cross section. 

It was assumed that the scattering nuclei were distributed according to a Maxwell distribution at tenqperature T and that neutrons were introduced into the system from a monoenergetic source Their results indicate that the actual spectrum Is peaked above that determined from Maxwell s law and the following linear relation holds. 

Region Graphite Process Tube Water Outer Fuel Inner Fuel 

Neutrons above thermal eziergles constitute a flux that Is best described by a distribution function e.g. the flux per unit range of energy. 

Xhe number of neutrons in a range dS at energy E (speed v) Is n(E)dB and the corresponding flux Is 0(s)dE n(s) v(E)dE In the areglon from about 1 ev to 100 kev the distribution function Is assumed to be inversely proportional to the energy. For the special case uhere all nuclei are pure scatterers  

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