The article deals with a radioisotope instrument for measuring the density and phase composition of flows in main oil pipelines. The instrument uses direct radiation and a gamma radiation beam scattered in space to obtain information on the flow composition (presence of free gas, water, clots and solid impurities) in the entire cross-section of the pipeline. The procedure of modeling such radiation beams by Monte Carlo method is described: the assumptions adopted in modeling and the sequence of operations. Further expected results of the work determination of the spatial distribution of the scattered radiation in the pipeline and the distribution of the registered radiation by energies.
