Detector Upgrade for Fast MeV X-Ray Imaging for Severe Accidents Experiments

Digital X-ray imaging systems for megaelectronvolt (MeV)-range photon beams are based on a combination of a scintillator screen and either a camera or an amorphous silicon array. To limit dose rate on electronics and enhance imaging device lifetime, the scintillator screen can be mirror-coupled to the camera. Performances of such devices are a compromise between exposure time and spatial resolution. These technical characteristics are especially scintillator-dependent. In this article, we present, in the first part, a performance evaluation of six different scintillators with a 9-MeV Bremsstrahlung X-ray source. The tested scintillators are composed of one microstructured CsI:Tl scintillator, two phosphor [Gd
₂
O
₂
S (GOS)] screens, and three transparent scintillators. These scintillators present a wide range of density, thickness, and conversion efficiency. The scintillator's performance assessment is based on the combination of light output and spatial resolution. The results are helpful to guide design and engineering of high-energy imaging devices adapted to specific requirements. In the second part, imaging performance comparison is done between our current GOS screen detector and a new CsI screen detector.