Noninvasive method for determining the three-dimensional density distribution in an inspected object employing modulation of compton-scattered gamma signals

A noninvasive measurement of the three-dimensional density distribution within an object is accomplished using a spectrometer to detect Compton-scattered photons from the inspected object that is irradiated by mono-energetic gammas from an isotopic source. This analysis describes the use of sets of virtual isogonic arcs and shells that, based on the Compton Scattering Law, represent the loci of scattering points having a common value of energy of scattered gammas-and that engulf the inspected object. A single-frequency electronic modulation on the voltage set points for each of the multi-channel analyzer energy bins allows modulation of these virtual isogonic surfaces within the inspected object to encode the scattered gamma flux from each voxel. Decoding of the detected gamma data is accomplished by multiplying it by electronic signals having frequencies identical to the voxel modulation frequencies. This is followed by integration and solution of a set of linear algebraic equations to produce an image of the density field.