Hard X-ray spectroscopy using small format GaAs arrays

We present preliminary results of X-ray measurements on a prototype 5 x 5 G aAs array. The device was fabricated from 40 mum thick epitaxial material a nd has a pixel size of 200 mum x 200 Irm and pitch 250 mum. Measurements fr om 5.9 to 100 keV were carried out both in our laboratory and at the HASYLA B synchrotron research facility in Hamburg, Germany. The average non-linear ity in the spectral response is <1% across the energy range 5.9-98 keV. Usi ng a 12 keV, 20 mum x 20 mum pencil beam, the uniformity in a pixels spatia l response was found to be better than 98%, The energy resolution at -40 de greesC is 400eV, FWHM at 5.9keV rising to 700eV at 98 keV. By best-fitting the expected resolution function to the entire data set, we derive a Fano f actor of 0.1440 +/- 0.005, assuming trapping noise is insignificant. Furthe r improvement in the energy resolution has been achieved by replacing the c onventional resistive feedback preamplifiers with a new resistor-less desig n. In this case, an energy resolution of 266 eV FWHM at 5.9 keV has been ac hieved at room temperature (23 degreesC) and 219 eV FWHM with only modest c ooling (-31 degreesC). (C) 2001 Elsevier Science B.V. All rights reserved.