Simulated performances of a very high energy tomograph for non-destructive characterization of large objects - 17167

The goals of the upgrading of Nuclear Measurement Laboratory's high-energy X-ray imaging system are to achieve a sub-millimeter spatial resolution and the ability to perform tomographies on very large objects (more than 100-cm standard concrete or 40-cm steel). This paper presents results on the detection part of the imaging system. The upgrade of the detection part needed a thorough study of the performance of two detectors: a series of CdTe semiconductor sensors and two arrays of segmented CdWO₄ scintillators with different pixel sizes. This study consists in a Quantum Accounting Diagram (QAD) analysis coupled with Monte-Carlo simulations. The scintillator arrays are able to detect millimeter details through 140 cm of concrete, but are limited to 120 cm for smaller ones. CdTe sensors have lower but more stable performance, with a 0.5 mm resolution for 90 cm of concrete. The choice of the detector then depends on the preferred characteristic: the spatial resolution or the use on large volumes. The combination of the features of the source and the studies on the detectors gives the expected performance of the whole equipment, in terms of signal-over-noise ratio (SNR), spatial resolution and acquisition time. (authors)