Nuclear Instruments and Methods in Physics Research B 97 (199.5) 567-571 JG!3 .__ _- i!iB ELSEVIER XSPRESS - X-ray signal processing for solid state detectors NIOMI B Beam Interactions with Yatwiels & Atoms electronics R. Farrow * , G.E. Derbyshire, B.R. Dobson, A.J. Dent, D. Bogg, J. Headspith, R. Lawton, M. Martini, K. Buxton DRAL Daresbury Laboratory, Keckwick Lane, Daresbury, Warrington WA4 4AD, UK EG & G Ortec Ltd., UK Abstract With recent improvements in synchrotron sources and X-ray optics great pressures have been placed on detector systems to produce higher count rates and better resolutions. Present high performance 13 element germanium detector systems can give reasonable count rates with good resolution (- 104-lo5 Hz per channel and - 250 eV FWHM @ s5Fe with 0.5 ps shaping time). However, these systems are restricted by limitations in both the detector and in the analogue pulse processing after the detector. With respect to the detector, increasing the number of channels without degrading the energy resolution is a great challenge due to increased crosstalk and capacitance. The analogue pulse processing electronics are significantly limited by the dead time introduced by the shaping amplifier. This dead time causes pulse pile-up at higher rates which leads to non-linearity and poor resolution. This paper describes the XSPRESS system which has been developed at Daresbury Laboratory for the new Wiggler II beamline 16. This system overcomes previous limits in both signal processing and detector fabrication to give great improvements in system performance. The signal processing electronics departs from standard analogue processing techniques and employs sophisticated adaptive digital signal processing hardware to reduce the dead time associated with each event to a minimum. This VME based technology allows us to vastly increase the count rate for each channel yet still retain the ability to gain very good resolution. The detector has been developed through a collaborative agreement with EG & G Ortec and packs an unprecedented 30 germanium crystals into an extremely small area whilst still retaining the energy resolution of smaller arrays. This system has increased throughput rate by an order of magnitude per channel and when all channels are implemented, an increase of at least two orders of magnitude for the whole array should be seen. Data has been taken using this system on the SRS at Daresbury Laboratory and these results will be given along with a detailed explanation of the operation of this system. 1. Introduction The availability of high quality energy resolving semi- conductor diode detectors for fluorescence X-ray absorp- tion fine structure (XAFS) experiments has allowed ever more dilute and complex materials to be studied. This has come about as the fabrication of the detectors has allowed increased energy resolution to be traded off against throughput rate. Element specific fluorescence radiation can thus be clearly separated from scattered radiation at lower energies or with higher throughput rates. Where energy resolution is not a major factor a scintil- lator based detector system can be used with correspond- ing throughput rates in excess of 100 kHz. However, * Corresponding author. where energy resolution is important, semiconductor detec- tors are utilised but the available processing electronics limits throughput rates to a few 10s of kHz. In an attempt overcome this limit, arrays of multiple semiconductor diodes have been built, each with their own channel of electronics. These arrays are built into a common cryostat and are now available as standard items from the major detector manufacturers. These systems will achieve count rates of 100s of kHz. Taking this parallel approach further would allow an increase in the number of detection elements but not without significant changes to the data processing electron- ics as conventionally this is NIM based analogue shaping amplifiers and single channel analysers. A point would arise at which the time taken to set up the detector electronics would prohibit its use. A new approach must be adopted to ease the setting up of the system and to improve the throughput rate for each channel. 0168-583X/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDI 0168-583X(94)00370-X XI. RECENT DEVELOPMENTS