Experimental verification of a hand held eleetronically-collimated radiation detector

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Conference Proceeding

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A hand-held electronically-collimated directional detector is being developed for gamma-radiation source localization. The system comprises a 6-sided box of detectors; Compton scatter events between pairs of detectors provide the source localization data. We report on experimental and simulation results for a partial prototype, with extrapolation to potential performance of a full detector system. The partial prototype used CZT detector modules to form two sides of the box geometry, with external signal processing and data acquisition components. Coincidence data were collected with the calibrated detector from Na-22, Cs-137 and Co-60 sources. The simulation model for charge collection in thick monolithic CZT accounted for charge trapping and sharing with estimation of hole and electron mobility, along with a linear approximation for charge sharing between pixels. By using calibration data from the prototype, the charge trapping model mimicked the average energy response, including tailing seen in the CZT energy spectra. Measured Compton-seatter data were compared for the three sources to the corresponding simulation results for a model of the two-sided prototype. Simulation results were also generated for the full 6-sided box geometry. The simulation model and prototype data showed that charge sharing and trapping contributed significantly to measured angular error and resolution for these CZT detector modules. The angular error typically was less than 5 degrees with angular resolution of 20-40 degrees FWHM, depending strongly on source location for the two-sided prototype. The 6-sided box simulation showed that reasonable direction-finding capabilities were possible even with the relatively coarse energy and spatial resolution of these CZT detector modules. Some discrepancies between simulation and prototype were due to the simple physics model used in the simulation; the charge trapping and sharing model is being incorporated into a more sophisticated GEANT4 simulation of the hand-held electronically-collimated detector system. Improvements to energy and spatial resolution of the detector modules should substantially improve overall system performance. © 2007 IEEE.

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IEEE Nuclear Science Symposium Conference Record

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