Development of a CZT spectroscopic 3D imager prototype for hard X ray astronomy

The development of focusing optics based on wide band Laue lenses operating from ~60 keV up to several hundreds of keV is particularly challenging. This type of hard X-ray or gamma ray optics requires a high performance focal plane detector in order to exploit to the best its intrinsic capabilities. We describe a three dimensional (3D) position sensitive detector prototype suitable for use as the basic module for a high efficiency Laue lens focal plane detector. This detector configuration is currently under study for use in a balloon payload dedicated to performing a high significance measurement of the polarization status of the Crab nebula/pulsar between 100 and 500 keV. The prototype is made by packing 8 linear modules, each composed of one basic sensitive unit bonded onto a thin supporting ceramic layer. Each unit is a drift strip detector based on a CZT crystal, irradiated transversally to the electric field direction. The anode is segmented into 8 detection cells, each comprising one collecting strip and 8 surrounding drift strips. The drift strips are biased by a voltage divider. The cathode is divided into 4 horizontal strips for the reconstruction of the Z interaction position. The detector readout electronics is based on three RENA-3 ASICs and the data handling system uses custom electronics based on an FPGA to provide the ASIC setting, the event handling logic and the data acquisition. We will describe the components and the status of the ongoing activities for the assembling of the proposed 3D CZT prototype and the result of the first performance tests on the CZT linear modules.