Qualification and development of fast neutron imaging scintillator screens

We have performed extensive testing and qualification of different commercial fast neutron scintillator screens in camera-based imaging detectors. These include organic scintillators and a ZnS:Cu scintillator mixed in a polypropylene (PP) matrix. Furthermore, we have developed simple and inexpensive in-house ZnS-based fast neutron imaging screens and their performance has been tested and compared to the aforementioned commercial ones. Furthermore, ZnS:Ag was mixed with high viscosity glycerol to create suspension type imaging screen. The ZnS concentration and the screen thickness have been optimized experimentally using sample screen pieces. The screens have been tested in spallation and fission spectra. The plastic scintillator performed the worst mainly due to its low light output, while the PP/ZnS screen the best. The in-house ZnS–epoxy screens produced about 60% of light intensity of its commercial counterpart, which is mainly due to the lower hydrogen density of the optical epoxy compared to polypropylene. A simple model of the converter/ZnS screen type was developed to help understand its properties and to optimize its performance. Some fast neutron radiographic images are shown to illustrate the capabilities of the screens.