text: Coefficient φ is dependent on the following;
  Which reflects the competition of two processes in the resonance region: absorption of neutrons and their deceleration. The cross section Σ, by definition, is analogous to the macroscopic absorption cross section with replacement of the microscopic cross section by the effective resonance integral J. It also characterizes the loss of slowing neutrons in the resonance region. As the U concentration increases, the absorption of resonant neutrons increases and hence fewer neutrons are slowed down to thermal energies. The resonance absorption is influenced by the slowing down of neutrons. Collisions with the moderator nuclei take neutrons out of the resonance region and are more intense the greater the moderating power . So, for the same concentration of U, the probability of avoiding resonance capture in the uranium-water medium is greater than in the uranium-carbon medium.
  Let us calculate the probability of avoiding resonance capture in homogeneous and heterogeneous environments natural uranium-graphite. In both media the ratio of carbon and U nuclei N/N=215. The diameter of the uranium rod is d=3 cm. Taking into account that ξC=0.159, σ=4.7 barn, we calculate the following probability;
  :  barn.
  Calculating the coefficients φ in homogeneous and heterogeneous mixtures, we get;
  : φ = e = e ≈ 0,65,
  : φ = e = e ≈ 0,93.
  The transition from homogeneous to heterogeneous medium slightly reduces the thermal neutron absorption in uranium. However, this loss is considerably overlapped by the decrease of the resonance neutron absorption, and the propagation properties of the medium improve.