A Dual-Modality Volumetric Gamma-Ray Imager for Near-Field Applications

There is an ever-growing need for instrumentation that provides both high-resolution and sensitive volumetric gamma-ray imaging capabilities across a wide range of photon energies in the near field. Such a technology is particularly critical to the fields of emergency response and contamination remediation, nuclear security and safeguards, and nuclear medicine. We aim to meet this technological demand by proposing a proof-of-principle prototype that has both volumetric coded aperture and Compton imaging capabilities in the near field. This article provides a detailed discussion of the coded aperture design and pattern optimization. We also evaluate the performances of the coded aperture and Compton imagers in terms of spatial resolution and sensitivity. The system exhibits a lateral resolution in full-width at half-maximum (FWHM) as good as 4.5 mm in the coded aperture mode and 2.1 mm in the Compton mode. Furthermore, the coded aperture and Compton modalities provide sensitivities on the order of $10^{-1}$ for energies below a few hundred keV and $10^{-3}$ for energies above a few hundred keV, respectively. We further demonstrate the imaging capabilities of the system by presenting 3-D reconstructions of near-field sources of various shapes and energies. To our knowledge, these results are the first demonstration of both volumetric coded aperture and Compton imaging in the near field via a single detection system.