Performance of a position-sensitive scintillation detector

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Abstract
The spatial resolution of a NaI(TI), 25 mm thick bar detector designed for use in position emission tomography was studied. The position along the 500 mm long detector was determined from the centroid of the light distribution in the crystal as measured by a linear array of photomultiplier tubes. A Monte Carlo computer simulation was performed to investigate the factors limiting the spatial resolution. The effect of various phototube configurations and crystal surface were studied. Since the resolution was affected by the width of the light distribution, the effect of sharpening the distribution was studied by modifying the front crystal surface with grooves cut perpendicular to the long axis of the crystal and by using non-linear preamplifers. The simulation predicted a spatial resolution (FWHM) of 3 mm with this crystal. Experimental measurements of spatial resolution were performed concurrently with the simulations. A modified grooved crystal was measured to have 4.0 mm spatial resolution, an improvement over the original crystal without grooves. With delay line pulse shortening, which increases the count rate capability of the detector, the grooved crystal had a 5.5 mm spatial resolution.

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