A study of a fine-pitched pixelated CdZnTe detector with a digital waveform acquisition system

Pixelated CdZnTe detectors were constructed with 19 × 19 pixels spaced by 500 μm pitch to study its feasibility in neutrino-less double beta decay search. Four selective pixels were connected to individual preamplifiers and relative timing response to gammas was investigated. Waveforms acquired by a single trigger from any arbitrary pixel can be sorted out for coincidence by taking the derivative of each waveform. The derivative method also allowed us to identify not only single or multi pixel events in each channel but also the nature of charge induction (direct hit pixel or response to neighboring pixels). This ability to identify each waveform type with an accurate time stamp gives us great flexibility to retain and reject freely preselected events and to successfully reconstruct pulse-height spectra. Two approaches, addition and subtraction methods, were investigated and both of them made it possible to refine untreated spectra and improved energy resolution was observed.