[en] A governing differential equation for the vector flux of transporting disintegrating particles has been synthesized from the 0-, 1-, and 2-velocity moments of the Boltzmann equation. Interaction (collisions) of the transporting particles S (e.g., radon) with a flow of environmental particles is implemented by modifications due to the application of Schluter concepts to the first and second moments. Hence, a provision is implemented to model transport in a many-fluid medium, where each component R is modelled by a characteristic particle mass, m_r; collision frequency with the transporting particle, nu_rs; gain factor delta_rs (defining energy loss of the transporting particle to the fluid component); the magnitude and direction anti V_r of R drift; and the temperature T_r of the R particle swarm. When all flows anti V_r are zero, then all transport is of a diffusive nature