192Ir Source Localization via Gamma Ray Skyshine using Large Volume Pixelated CdZnTe

The direct line-of-sight between a detector and strong gamma-ray source can be heavily shielded in urban environments. In extreme scenarios, such as measuring a source through several buildings, little-to-no gamma-ray flux streams from the source direction due to building attenuation. This unknown, non-spatially-smooth attenuation from buildings hinders traditional 1/r²-based localization in urban environments. Air-scattered gamma rays, known as skyshine, offer a complimentary signal that is a weak function of unknown ground-based shielding between the source and detector. Skyshine can be leveraged to localize strong gamma-ray sources, without the use of count rates, in attenuation heavy scenarios. Skyshine-based localization was demonstrated for a 83 Ci ¹⁹²Ir source in a silo geometry using a H3D H420 CdZnTe detector. Source directionality was successfully estimated from coded aperture reconstructions of skyshine gamma rays at distances ranging from 25-150 m.