Reliability of 3D Pixelated CdZnTe System in the Quantitative Assay of Radioactive Waste: a Demonstration

Several tests have been performed with an H420 pixelated CdZnTe imaging spectrometer to evaluate its capability to provide reliable imaging and quantification results. Waste barrels prepared by National Physical Laboratory (NPL) for the Nuclear Industry Proficiency Test Exercise held in 2019 and 2021 were measured, detecting clear 241 Am, 137 Cs, and 60 Co photopeaks in collected gamma-ray spectra, while Compton and coded aperture imaging were used to localize sources and reconstruct their 2D/3D spatial distributions. Point-kernel-based activity quantification techniques were used to estimate isotope-specific activities, with results close to those obtained by High Purity Germanium detectors and to true NPL declarations. Furthermore, in order to test the reliability of the quantification method for a large span of energies/distances/materials, a hot 226 Ra source was measured in multiple geometries, obtaining consistent data, although difficulties in measuring peak areas on large, non-linear continua were observed. The results presented in this work suggests that high-resolution 3D pixelated CdZnTe detectors can be used for typical waste quantification problems and can reliably assay complex geometries thanks to flexibility of the quantification algorithm. Moreover, the spatial information on the radionuclides’ distribution from gamma-ray imaging can be used as input for a heterogeneous radioactivity model to minimize systematic uncertainties.