Identification of Intervening Materials in Gamma-Ray Spectroscopy Measurements Using Angularly Deconvolved Spectra With Multiple Sources in the Field of View

The mass thickness and atomic number of materials shielding radioactive sources emitting multiple resolvable gamma-ray energies can be characterized by measuring the attenuation and Compton scatter of emitted gamma rays in recorded spectra against estimated values for a suite of materials and thicknesses. Compton imaging using a maximum-likelihood expectation maximization-based reconstruction can be used to separate angular spectra allowing simultaneous characterization of multiple shielded sources. Using the described algorithm on experimental
¹³³
Ba data, we demonstrate estimation of mass thickness and atomic number for iron, tin, and lead shields with another bare source in the field of view with average standard error of 0.6 g/cm
²
and 1.5, respectively, while an aluminum shield is reconstructed with ambiguous atomic number but correct thickness.