New position algorithms for the 3D CZT drift detector

The 3D position sensitive CZT detector for high energy astrophysics developed at DTU has been investigated with a digitizer readout system. The 3D CZT detector is based on the CZT Drift Strip detector principle and was fabricated using REDLEN CZT crystals (20 mm × 20 mm × 5 mm). The detector contain 12 drift cells, each comprising one collecting anode strip with 4 drift strips, biased such that the electrons are focused and collected by the anode strips. 3D position determination is achieved using the anode strip signals, the drift strip signals and the signals from 10 cathode strips. For the characterisation work, we used a DAQ system with a 16 channels 250 MHz 14bit digitizer, SIS3316. It allowed us to handle 4 detector cells and analyse the pulse shapes of all electrodes. The 3D CZT setup was characterized with a fine collimated high-energy (Cs137, 662 keV) monochromatic beam at DTU Space. With the developed position algorithms we demonstrate improved position determination compared to the previous read out system based on analog electronics. Position resolutions of 0.4 mm FWHM in the X-, Y- and Z-direction were achieved and the obtainable energy resolution was ∼6 keV FWHM at 662 keV. The timing information does allow identification of Compton events. These characteristics are very important since an important aim of the 3DCZT development is to realize an imaging detector which can serve in a Compton camera for astrophysical studies.