  The complexity of the neutron transport phenomenon throws its shadows on
every physical system wherever neutron is produced or absorbed. The Monte Carlo
N-Particle Transport Code (MCNP) was used to investigate the flux perturbations
in the neutron field caused by an absorber. The geometry of the present
experiment was designed to reach a simulation of an isotopic neutron field. The
neutron source was a ${}^{241}$AmBe with the production physics of neutrons is
dependent only on alpha-beryllium interaction and is independent of what
happened to the neutron after it was generated. The geometries have been
designed to get a volume of uniform neutron densities within a spherical volume
of radius 15 cm in every neutron energy group up to 10 MeV. Absorbers of
different dimensions were placed within the volume to investigate the field
perturbation. Different neutron absorbers were used to correlate the phenomenon
to the integral cross-section of the absorber. Flux density inside and outside
the absorber samples was determined, while the spatial neutron flux
distribution produced by the AmBe source without an absorber was taken as a
reference. This study displayed that absorbers of various dimensions perturb
the neutron field in a way that is dependent on the absorption and scattering
cross-sections, particularly in the neutron resonance region. Unlike the simple
picture of reducing the number density of neutrons, the perturbation was found
to influence the moderation of neutrons in the medium, significantly above 1
MeV.
