CZT detectors - their development and use in the field of X-ray astrophysics 

First, I will discuss our efforts to develop fine-pitch (<=250um) pixelated  Cadmium Zinc Telluride (CZT) detectors. CZT is a material of choice for detection of X-rays in the hard X-ray energy band with excellent spectral and spatial resolution without the necessity of cryogenic cooling. Development of fine-pitch pixelated detectors is driven by recent breakthroughs in grazing incidence mirror technology, which allow the next-generation of hard X-ray telescopes to achieve angular resolution between 5 and 10 arc seconds. As a consequence, pixelated hard X-ray detectors with pixels on a grid with a lattice constant of <=250um are required by the next-generation of hard X-ray telescopes to harvest the full potential provided by the progress in the grazing incidence mirror technology. I will show the first successfully fabricated sample of fine-pitch CZT detectors in our lab, and I will discuss the challenges thatwe faced during the fabrication process and the data acquisition phase. The successfully fabricated CZT detectors have pixelated anodes with varying pixel pitch (between 200um and 500um) and varying pixel size (between 100um and 250um).
 
In the second part of the talk, I will describe the design and performance of the X-Calibur - a hard X-ray polarimeter developed at Washington University, which utilizes CZT detectors. I will also talk about the Compton-scattering polarimeter utilizing, instead of a plastic scintillator like in the X-Calibur, a compressed lithium hydride (LiH) slab. The use of LiH as a low-Z scattering material pushes the low energy detection threshold down to few keV, and makes this design a great solution for future spaceborne polarimetric missions. I will discuss the laboratory setup of LiH Compton-scattering polarimeter that we built and characterized its performance with the soft X-ray polarized source (also built in our lab specifically for this project). I will show results of the first polarimetric measurements performed with this system setup where we clearly see the polarization signal at 7.9 keV.