Use of virtual Frisch-grid CdZnTe detectors to attain sub-millimeter spatial resolution

The goal of our study was twofold: To determine the distribution of signals in position-sensitive CdZnTe (CZT)-based virtual Frisch-grid detectors (VFGDs) with side-sensing pads, and to evaluate the feasibility of accurately measuring the X- and Y-coordinates where a photon interaction occurs within a single VFGD module. Accordingly, we collected signals from an anode, and from four or eight sensing pads attached to four sides of a CZT crystal. We assessed the anode's energy spectra and derived histograms from the side electrodes so to evaluate the feasibility of employing VFGDs as imaging devices. Using a highly collimated 30-keV X-ray beam at the National Synchrotron Light Source (NSLS), and applying some corrections to the raw signal data, we found that the signals acquired from one side of the detector were well separated from those measured at the opposite side. We also determined the photon interaction points by conventional Anger logic and via a more sophisticated statistics-based positioning (SBP) algorithm. With the current VFGD configuration, preliminary results showed that our positioning methods could increase the resolution above the intrinsic resolution of the VFGD (6 mm). Using SBP, we achieved a resolution below 1 millimeter for low-energy X- and gamma-rays.