Evaluation of undoped ZnS single crystal materials for x-ray imaging applications

摘要

ZnS-based materials have a long history of use as x-ray luminescent materials. ZnS was one of the first discovered scintillators and is reported to have one of the highest scintillator efficiencies. The use of ZnS for high energy luminescence has been thus far limited to thin powder screens, such as ZnS:Ag which is used for detecting alpha radiation, due to opacity to its scintillation light, primarily due to scattering. ZnS in bulk form (chemical vapor deposited, powder processed, and single crystal) has high transmission and low scattering compared to powder screens. In this paper, the performance of single crystalline ZnS is evaluated for low energy x-ray (<10 keV) imaging. For these applications, a scintillator needs to be thick enough to absorb the incoming x-rays and to provide sufficient gain, but thin enough to allow for a good spatial resolution. The scintillators also need to have a good radiation hardness, a fast decay time, and low levels of afterglow. We present a trade study which compares the calculated scintillation gain and absolute efficiency for low energy x-rays (<10 keV) comparing thin (<100 μm) ZnS to CsI:Tl, Bi_4Ge_3O_(12) (BGO), and Y_3Al_5O_(12):Ce (YAG:Ce). The study also gives insight into the spatial resolution of these scintillators. Further, photoluminescence (PL) and PL excitation (PLE) of several undoped ZnS single crystals is compared to their Radioluminescence (RL) spectra. It was found that the ZnS emission wavelength varies on the excitation source energy.