Patent ID: 7402796

Claim:
A method of monitoring flow in a flow pipe, the method comprising: providing a flow pipeline having a photon detector at a first position on the periphery of said pipe, a first photon source at a second position on the periphery of said pipe, said detector and first source defining a first chord across said pipe, and one or more additional photon sources at positions on the periphery of said pipe defining one or more additional chords across said pipe, wherein the first photon source and the one or more additional photon sources are of different photon energies; determining the density across said first chord from the count rate detected from the first source by the detector; and determining the densities across said one or more additional chords from the count rate detected from the one or more additional sources by the detector, wherein the additional chords are chosen to have successively decreasing length across said pipe relative to said first chord.