R. C. Farrow

Combined energy dispersive EXAFS and x‐ray diffraction

An in situ experiment to measure both x‐ray absorption spectroscopy and x‐ray diffraction of aurichalcite is described. The experiment uses position sensitive detectors to enable both data sets to be collected while the sample is slowly decomposed in air and then reduced in hydrogen.

XSPRESS — X-ray signal processing electronics for solid state detectors

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 (∼ 10 4 –10 5 Hz per channel and ∼ 250 eV FWHM @ 55 Fe with 0.5 μs 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.

XSTRIP: a silicon microstrip-based X-ray detector for ultra-fast X-ray spectroscopy studies

For a number of years, an exciting and important area of synchrotron radiation science has been X-ray absorption spectroscopy fine structure studies of dynamically changing samples on the sub-second time-scales. By utilizing this technique, precise measurement of detailed structural changes can be investigated during a chemical or phase change reaction without the need for repeated experiments or expensive stopped flow techniques. Until recently, instrumentation to facilitate these studies has been based on commercially available detectors developed predominantly for other applications. Whilst these systems have yielded quality science, they have been subject to a number of fundamental limitations, particularly their speed, linearity and dynamic range. We have developed a new detector, XSTRIP, to overcome some of these. This new instrument marries dedicated silicon microstrip technology with specialist low noise, custom developed, fast readout integrated circuits, to yield an instrument that will unlock whole new areas of science to researchers. This paper will discuss some of the drawbacks of historical systems, give details of the XSTRIP system and also present the operating parameters of the system. In addition, some of the initial scientific experimental results will also be presented.

A gas microstrip wide angle X-ray detector for application in synchrotron radiation experiments

Abstract The Gas Microstrip Detector has counting rate capabilities several orders of magnitude higher than conventional wire proportional counters while providing the same (or better) energy resolution for X-rays. In addition the geometric flexibility provided by the lithographic process combined with the self-supporting properties of the substrate offers many exciting possibilities for X-ray detectors, particularly for the demanding experiments carried out on Synchrotron Radiation Sources. Using experience obtained in designing detectors for Particle Physics we have developed a detector for Wide Angle X-ray Scattering studies. The detector has a fan geometry which makes possible a gas detector with high detection efficiency, sub-millimetre spatial resolution and good energy resolution over a wide range of X-ray energy. The detector is described together with results of experiments carried out at the Daresbury Laboratory Synchrotron Radiation Source.

A novel application of silicon microstrip technology for energy-dispersive EXAFS studies

A prototype X-ray detector for energy-dispersive EXAFS has been developed and tested to demonstrate the principle of using silicon microstrip detector technology for this application. Testing took place at the UK Synchrotron Radiation Source, where the absorption spectra of a 5 microm Ni foil and a 25 mM NiCl(2) solution were obtained.

Initial data from the 30-element ORTEC HPGe detector array and the XSPRESS pulse-processing electronics at the SRS, Daresbury Laboratory

Following the completion of the collaborative project between CLRC Daresbury Laboratory and EG&G ORTEC to develop the worlds first 30-element HPGe detector for fluorescence XAFS, it has now been tested and commissioned at the SRS. The system was commissioned with the XSPRESS digital pulse-processing electronics and this has demonstrated processed count rates in excess of 10 MHz. Initial data have been recorded and are presented.

CHARACTERISATION OF RETICON AND HAMAMATSU PHOTODIODE ARRAY AND THE SUBSEQUENT DEVELOPMENT OF HIGH PERFORMANCE VME-BASED DETECTOR SYSTEMS OPTIMISED FOR ENERGY DISPERSIVE EXAFS

Abstract Energy Dispersive EXAFS is an established and successful technique employed at Daresbury Laboratory for the study of dynamic experiments. At the heart of this technique is an in house developed high-performance VME-based detector system using a photodiode array. This system originally used a Reticon RL1024S array but extensive investigation of three other photodiode arrays namely the Reticon 512T, 512SB and the Hamamatsu S3904 has enabled their characterisation and the subsequent development of optimised drive and signal processing electronics. This has provided two further systems which exhibit improved signal to noise, excellent linearity and increased operational speed.

A multielement solid‐state detector system for use on the SRS materials science Station 9.3

This article describes the design of a multielement solid‐state detector system for use on the SRS materials science Station 9.3. The detector system is discussed in detail and test data are presented. The current system consists of 13, 8‐mm diam, germanium diodes mounted in a single cryostat. The system operates with a 0.5‐μs shaping time and achieves better than 200‐eV resolution at 5.9 keV. Rate and resolution characteristics of the system are discussed with a view to future improvements in the system.

A solid state detector for soft energy extended x‐ray absorption fine structure measurements

Following the success of solid state detector systems for extended x‐ray absorption fine structure studies at high x‐ray energies, there is now an increasing demand for similar devices capable of operating in the soft x‐ray energy range below about 3 keV. Recent developments in sophisticated detector fabrication techniques now make the construction of specialized devices, suitable for high quality spectroscopy in this energy range, a practicable proposition. We present the results of extensive testing of a new detector developed specifically for use in the sub‐3 keV energy range. We have measured energy resolutions of less than 125 eV full width at half maximum at sulfur and silicon Kα energies and the ability of the detector to achieve this resolution at the copper Lα line has also been shown. Finally we demonstrate the potential of this device in a study of trace dopants in bulk silicon based quantum dot glasses.

A high performance VME-based detector system for subsecond energy dispersive EXAFS

Abstract New detector instrumentation developed at Daresbury Laboratory enables high quality Energy Dispersive EXAFS (EDE) data to be collected in timescales of less than a second using a 1024 element Reticon linear array. Characterisation of the array has been performed which has enabled optimised drive and signal processing electronics to be developed. The use of these new electronics has significantly improved both signal to noise ratio at high speed and flexibility over previous systems. The reduction of nickel formate has been studied using this system and this data will be presented.