AbstractA simple formula which describes energy—space distributions of streaming neutrons in ducts and slits is described. The albedo model was used in the derivation of the formula. The spatial distribution of neutron fluxes in the gaps was represented by those of direct, doubly scattered and eight-time scattered albedo fluxes. The energy spectra of the neutrons were expressed by the power of an albedo matrix.In the slit problem, the leakage component plays an important role. A point kernel calculation, which was made based on ANISN calculated fluxes, was combined with the above formula to account for the contribution from the leakage component.The proposed calculation method was tested by a variety of 14 MeV neutron streaming experiments in concrete or polyethylene gaps, and by a Monte Carlo calculation for concrete ducts. The proposed method reproduced the reference data within a factor of two to three in all of the tested cases.