Large area gamma-ray imaging detector based on high-resolution CdTe diode

We are developing a large array detector composed of 1024 individual CdTe diodes. Each detector has the dimensions of 1.2 mm × 5.0 mm and a thickness of 1.2 mm. An edge-on geometry is used for the injection of γ-rays, to obtain a cross-section thickness of 5 mm. With this geometry, the distance between the two electrodes can be kept small, and we can therefore apply the high electric field which is necessary to achieve a high energy resolution (by reducing the low energy tail) and also to sustain the long-term stability of the CdTe diode. Signals from each detector element are fed into newly developed low noise ASICs. We use 32 chips for the readout of 1024 elements. In this paper, we report the basic characteristics of the individual detectors and the overall performance of the gamma-camera. Design of the readout electronics system is also described.