We carried out experiments of self-diffusion in single crystalline silicon at a temperature of 900 °C by a method that is based on neutron reflectometry in combination with 29Si/28Si isotope multilayers. The experimental reflectivity pattern shows artificial Bragg peaks due to isotope periodicity and is fitted by the program Parratt32. Diffusivities are calculated from the roughness parameter of the isotope interfaces. The results are compared to that one obtained from a simple analytical expression on the reduction of the Bragg peak. The results exhibit that both methods deliver identical diffusivities within error limits. The diffusivity of 4 × 10−22 m2 · s−1 does not depend on annealing time for diffusion on a length scale of 1–6 nm and is in good accordance to literature data, ranging between 1 and 10 × 10−22 m2 · s−1. The results demonstrate that the neutron reflectometry method is well suited to determine self-diffusivities in single crystalline silicon at very short length scales.