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July 7, 2004 NSLS 2004 Annual Users’ Meeting WorkshopBetter ways to see the light: Advanced detectors for synchrotron radiationThe workshop attracted 62 registrants, who enjoyed a wide range of talks about the latest in detector developments for synchrotron radiation (SR) applications. The following is a very brief resumé of the talks presented. Many people think the center of this activity is in Europe these days, and to bring us up to date with what is happening over there, we heard Dr. Gareth Derbyshire (from the Rutherford-Appleton laboratory in the UK) talk about "Detector Developments for Synchrotron Radiation in Europe". He described work underway at the Daresbury and Rutherford laboratories, as well as work being pursued by the Swiss Light Source in collaboration with Centre Européenne pour la Recherche Nucléaire (CERN). In particular, he stressed the need to provide advanced detector systems to the UK's Diamond light source, currently under construction, ready for use on 'day 1'.
There are many interesting detector developments happening in fields other than SR. The next speaker, Dr. Oswald Siegmund, is from the Space Sciences Laboratory at UC Berkeley. In his talk, "Microlithographic Silicon-Based Microchannel Plates and Readout Techniques for Photon and Particle Detection" he told us of some interesting developments in microchannel electron multiplier device technology, in particular the use of micromachining techniques to make precision microchannels in silicon wafers. Such devices offer much improved uniformity and reduced noise over conventional drawn glass structures. He also described readout electronics which are capable of providing good spatial resolution in one and two dimensions, for use with these new channel plates. There is a real lack of detector technologies which are suitable for hard x-ray detection. Perhaps the most promising at the moment is cadmium-zinc telluride (CZT). This material is not ideal, but the use of special signal processing techniques can be helpful. Gabriella Carini (Brookhaven National Laboratory) spoke about "A New Integrated Circuit for Coplanar-grid Detector Readout". The coplanar grid detector has a special electrode structure which can mitigate the poor hole mobility in these room-temperature semiconductor detectors. The talk described a new microcircuit designed by the BNL Microelectronics group, which provides enhanced capabilities for such devices. A key part of any detector system which is to be truly useful is the software used to control the detector and analyze the data produced. Dr. Chris Ryan, from Commonwealth Scientific & Industrial Research Organization (CSIRO) in Australia, has developed "A New Technique for Real-time Spectral Deconvolution of Energy-resolving Detector Data" which can generate quantitative elemental maps from fluorescence microprobe data, in real-time. Simple methods using pulse-height windows can lead to serious errors in elemental identification due to strong peak overlaps. Chris's technique is able to account for all these overlaps, together with other artifacts such as escape peaks, and build up an elemental map photon-by-photon. An exciting development which is beginning to become more accessible is that of very high-resolution x-ray detectors based on cryogenic superconducting technology. Kent Irwin (National Institute of Standards and Technology, Boulder, CO) in his talk "Cryogenic Microbolometer X-ray Detectors” brought us up-to-date on these devices. They can reach single-digit eV resolution in the x-ray region, a remarkable achievement. The disadvantage of these detectors is that they are rather slow, and Kent described how his group is working to overcome this limitation by making large arrays of detectors, and how the superconducting quantum interference device (SQUID) technology used to read them out can be integrated into such an array device. Even the best detectors sometimes need help, and in the absorption spectroscopy field this is particularly true. In his talk, "Multilayer Optics for Fluorescence Detectors", Ke Zhang (BioCAT, Argonne National Laboratory) described the development and application of multi-element analyzer systems based on synthetic multilayer optical elements. The instrument he presented provides an efficient filter which only allows a particular spectral line to pass to the detector. The multiple elements provide enhanced solid angle and hence efficiency. Perhaps the most powerful driver for advanced detector development in the synchrotron community has been the demands of macromolecular crystallography. The talk by Dr. Edwin Westbrook (Molecular Biology Consortium Inc.) titled "Silicon Pixel Array Detectors for Protein Crystallography", described some new ideas for fabricating detectors using non-traditional processing techniques. The result is a technology which can produce efficient arrays of detectors with excellent properties. One point which is unique to this technology is that the arrays do not have any dead area around the edges, so detectors can be easily tiled together to make large area systems without any lost image regions. Tae Joo Shin (NSLS) then told us about his work towards using 2-D position-sensitive proportional counters (PSPCs) for x-ray speckle experiments. Present speckle experiments typically use either a single point detector and photon-counting with high time resolution, or a CCD area detector, which has a readout time of at best some 10's of milliseconds. PSPCs have the potential to combine the advantages of a photon counting detector and an area detector. Preliminary experiments to characterize and improve the performance of such detectors to make them suitable for speckle were described. Our final talk was to have been given by Dr. Mark Rivers (Univ. Chicago). Although circumstances prevented him from giving the talk at that time, it was rescheduled for a few days later. It also concerned the software implications of advanced detector systems. This area of development is extremely important, and the difficulties and required effort frequently underestimated. Mark told us about the software solutions he has developed for interfacing area detectors, in particular CCD devices, to data acquisition systems based on the EPICS framework. The breadth and depth of these talks only scratch the surface of what I believe is the last remaining barrier to full utilization of our powerful synchrotron facilities. I look forward to hearing much more of these developments at future meetings. Acknowledgements FOR MORE INFORMATION Gianluigi De Geronimo |
The National Synchrotron Light Source at Brookhaven National Laboratory in New York, is a national user research
facility funded by the U.S. Department of Energy's Office of Basic Energy Science. The NSLS operates two electron
storage rings: an X-Ray ring and a Vacuum UltraViolet (VUV) ring which provide intense light spanning the electromagnetic
spectrum from the infrared through x-rays. Each year over 2300 scientists from universities, industries and government
labs perform research at the NSLS.
