CZT detectors as MeV gamma-ray calorimeters with excellent position and energy resolution

Several astrophysics and nuclear physics applications require the detection of MeV photons with good position and energy resolution. For certain applications cadmium zinc telluride (CZT) detectors might be the detector option of choice: they achieve better position and energy resolution than scintillation detectors and can be built more compact and more economically than Ge detectors. In this contribution, we briefly describe astrophysics and nuclear physics applications in which we are interested. Subsequently, we describe the results of Monte Carlo simulations of an "MeV Calorimeter": a 10 cm to 30 cm thick detector made of closely packed 1.5times1.5times1 cm³ large pixellated CZT detector units, each pixel being read out individually. Our simulation shows that the spatial extent of the energy deposition inside the CZT together with the electronic properties of present-day CZT substrates limits the theoretically achievable performance of such a calorimeter. The conclusion holds even if one considers detector modules with very small pixels and assumes correction of the anode signals with electron drift times. Finally, we discuss crucial detector issues that need to be addressed to improve the performance of CZT calorimeters