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Coded apertures were originally developed by the high-energy astrophysical community for use in imaging high-energy
photons (x- and γ-rays) for which focusing optics are ineffective. We are now taking what was developed as a tool for
use in the extreme far field at high energies to encode spatial information at optical wavelengths in the extreme near field
to enhance the performance of position-sensitive x- and gamma-ray scintillator detectors. Spatial resolution for events
within bulk scintillators is limited by the size of the light “spot” available at the sides of the scintillator, where
phototransducers convert the light to an electrical signal. The ability to localize an event is determined by how well one
can determine the centroid and the size of the spot. Generally, performance is limited to many millimeters in all three
spatial dimensions, and one cannot resolve simultaneous events that are closer together than the width of the light spot
(frequently of order 10 mm). For this reason, many applications requiring the finest spatial resolution subdivide the
scintillator into tiny elements and use a digital approach to determine event location. However, that technique
significantly complicates the overall instrument and sacrifices energy resolution because the light collection efficiency
varies with event location within the subdivided scintillator. We are building a device that overcomes these shortcomings
by using an optical coded-aperture shadow mask between a bulk crystal and a position-sensitive phototransducer.
Simulations indicate that we can achieve millimeter-scale localization in all three spatial dimensions while resolving
simultaneous energy depositions. The technique and progress toward its realization will be presented.
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