Maximizing the Spatial Resolution for Single Crystal Diffractometer Detectors

A bright, fast, high spatial resolution scintillator will improve the spatial resolution and throughput of the single crystal diffractometer at the Spallation Neutron Source at Oak Ridge National Laboratory. This is because novel detector technologies that can provide 300 µm or better spatial resolution with gamma rejection better than 10-6 are needed to enable efficient measurement of small single crystals for diffraction and diffuse scattering measurements. Recent advances in large area neutron sensitive anger cameras at Oak Ridge National Laboratory ORNL) based on SiPM arrays have intrinsic resolutions that can fulfil the diffractometer requirements, but the currently used GS20 scintillators limit the overall performance of the system. Higher resolutions are critical for new instruments proposed for the second target station at SNS such as EWALD, where detectors requiring resolutions near 300 µm have been proposed. We propose to address the limitations of GS20 by using an advanced scintillator, made in a large area, microcolumnar film format that heretofore was not possible to grow because of the extreme hygroscopic nature of the material. This choice is based on the known high brightness of the material, which emits a relatively low number of photons/MeV, but is expected to yield as many as 50,000 to 100,000 photons per thermal neutron interaction, a factor ~8 to 16 times higher yield than current GS20 glass. The high thermal neutron efficiency of this material implies that only ~1.0 mm of scintillator thickness is needed to absorb about 60% of 1Å neutrons. The very thinness of the scintillator helps significantly in discriminating against gammas by minimizing the probability of both photoelectric absorption and light conversion efficiency for gammas. Finally, one of the key innovative approaches we plan to pursue is to realize large-area co-doped scintillators. These advanced materials promise fast temporal responses with our initial data showing the decay of ~50 ns, thereby significantly reducing the potential dead-time. In the Phase I, RMD Inc. will use physical vapor deposition to make screens of scintillation material, as well as dope or co-dope the material with divalent or trivalent ions to improve the speed. The entire deposition and sealing process will be carried out in a moisture free atmosphere using a newly developed technique at RMD. The properties of the scintillator screens will be thoroughly characterized at RMD Inc. with neutrons, gammas and X-rays, and then the feasibility will be tested at ORNL HFIR/SNS facility. RMD’s scintillator/detector will be an excellent choice for neutron detectors for any facility that runs neutron experiments. For example, at Oak Ridge National Laboratory, large-area detectors at the Spallation Neutron Source are used for neutron scattering experiments and in materials research for a variety of applications. There are no established requirements because each detector is designed for a specific research purpose. Including the U.S. facilities, there are 45 neutron research centers located around the world that will want to take advantage of our technology.