Layerwise sensing in $X$-ray tomography in the polychromatic case

An $X$-ray tomography problem that is an inverse problem for the transport differential equation is studied. The absorption and single scattering of particles are taken into account. The suggested statement of the problem corresponds to stepwise and layerwise sensing of an unknown medium with initial data specified as the integrals of the outgoing flux density with respect to energy. The sought object is a set on which the coefficients of the equations suffer a discontinuity, which corresponds to searching for the boundaries between the different substances composing the sensed medium. A uniqueness theorem is proven under rather general assumptions and a condition guaranteeing the existence of the sought lines. The proof is constructive and can be used for developing a numerical algorithm.