Radiative capture of ultracold neutrons in a two-layer target

The probabilities of the elastic scattering and capture of ultracold neutrons in two-layer targets where the upper and lower layers are, respectively, thin and thick in relation to the neutron wavelength λ have been calculated. It has been shown that the macroscopic cross section for (n, γ) reactions in the upper layer varies in rather wide limits, depending on the properties of the layers (in particular, this cross section can vanish). The corresponding cross section in the lower layer is always larger than the value it would take in the absence of the upper layer (the former can exceed the latter by a factor of 4)