Abstract Details
| Name: Tanmoy Chattopadhyay Affiliation: Physical Research Laboratory Conference ID: ASI2016_622 Title : Generation of Response Matrix for multi-pixel CZT detectors Authors and Co-Authors : Dr. Santosh Vadawale, Physical Research Laboratory, Ahmedabad, India Prof. A. R. Rao, Tata Institute of Fundamental Research, Mumbai, India Prof. Dipankar Bhattacharya, IUCAA, Pune, India Mr. Mithun N. P. S., Physical Research Laboratory, Ahmedabad, India Abstract Type : Poster Abstract Category : Instrumentation and Techniques Abstract : Cadmium Zinc Telluride (CZT) detectors have been the workhorse in hard X-ray astronomy for a decade now, implemented in many X-ray observatories e.g. SWIFT, NuSTAR and more recently in ASTROSAT. Response matrix for CZT detectors requires precise modelling of the X-ray lines as a function of energy. Instead of showing simple Gaussian feature, these lines exhibit a long tail at lower energies because of trapping of the charge carriers due to their low mobility (µ) and lifetime (τ). The effect is found to be more significant for high energy photons as the probability of charge loss increases with the depth of interaction. Therefore, precise line modelling in case of CZT detectors needs accurate measurement of µτ values for electrons and holes. For pixelated detectors, other significant components in the line modelling come from the crosstalk between the pixels due to charge sharing, fluorescence photons and Compton scattering. Charge sharing is expected to be quite significant making the CZT line profile further complicated. We have developed a numerical model taking into account all these physical processes to predict the CZT line shapes properly. The model is written in S-LANG and incorporated in spectral fitting package ISIS. Here we present the details of the numerical model and experimental measurements of mobility and lifetime of the charge carriers and the inter-pixel charge sharing fractions for 4 cm X 4 cm and 5 mm thick CZT detectors with pixel dimension of 2.5 mm X 2.5 mm, procured from Orbotech Medical Solutions (similar to the modules used in CZTI, Astrosat). In order to understand the charge sharing in the detectors in more detail, we did further experiments, results and implications of which will be discussed in this presentation. |