CZT detectors read out with the RENA-2 ASIC

Multiple-site interactions initiated by Compton scattering are the primary interaction processes of gamma-rays in CZT in ~0.2 - several MeV range. Thus, exploiting gamma-rays as directional and spectral diagnostic probes requires detectors with 3-D resolution that resolve and measure individual interaction site´s locations and energies. Desirable capabilities for Compton telescopes appear to be a spatial resolution of ~1 mm and an energy resolution of ~1 percent. Such capabilities are also important for coded mask imagers above 250 keV, where 3-D resolution can greatly improve the identification of a gamma-ray´s initial interaction site, which is crucial for imaging. Significantly improved spectral resolution can be anticipated with CZT when multi-site interactions are resolved. This will allow each site´s energy signals to be corrected for the site´s specific signal loss characteristics, and the summed energies will then provide an accurate measure of the incident gamma-ray energy. We report on progress toward the development of 5 - 10 mm thick CZT detectors and electronics that are pursuing these objectives. Position sensing is provided by anode pixels with ~1 mm pitch for x-y positions and charge drift times for z-positions. Detectors are read out with the new RENA-2 ASIC. This chip contains preamplifiers, shaping amplifiers, threshold triggering, and peak detection for each of its 36 channels. To optimize energy resolution for various detector types and event rates, the RENA-2´s peaking times and other parameters are adjustable. Each channel has a novel fast time stamp function that can record interaction times to ~10 nsec, allowing precise measurements of charge drift times and making PET imaging possible. The detector and ASIC designs are described and results are presented on tests of thresholding, energy resolution, and time resolution