Velocity distribution of Brownian particles at the input of a closed detector

The velocity distribution function of passive-tracer particles in a gas flow on a closed boundary of a given spatial region is found for various relations between the regular drift and diffusion. An example of calculation of the velocity probability density on the boundary of a region comprising a source of particles is given.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 1, pp. 86–93, January 2005.