D. Bogg

Simultaneous studies of reaction kinetics and structure development in polymer processing.

The simultaneous time-resolved study of structure development and reaction kinetics during polymer processing is an experimental method that has great potential in developing a deeper understanding of the parameters that govern the formation of structure and therefore polymer properties. A combination of synchrotron radiation small-angle x-ray scattering and Fourier-transform infrared spectroscopy experiments have been performed on a series of model segmented block copolyurethanes. These studies confirm that the driving force for structure development in polyurethanes is the thermodynamics of phase separation rather than hydrogen bonding.

Raman spectroscopy combined with small angle X-ray scattering and wide angle x-ray scattering as a tool for the study of phase transitions in polymers

A novel combination of simultaneous experimental techniques has been developed as a tool for the study of phase transitions in polymers. Based upon a small angle x-ray scattering (SAXS) synchrotron radiation beamline it has been shown to be feasible to collect, in addition to the time-resolved SAXS data, wide angle x-ray scattering and Raman spectroscopy data with a time resolution of a few seconds.

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.

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 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.

X‐ray signal processing electronics for solid state detectors

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 (∼104–105 kHz per channel and ∼250 eV FWHM at Fe55 with 0.5 μs shaping time). However, these systems are restricted by limitations in both the detector and in the analog 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 analog pulse processing electronics are significantly limited by the dead time introduced by the shaping amplifier. This dead time causes pulse pileup at higher rates which leads to nonlinearity 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...

Simultaneous time-resolved synchrotron X-ray scattering studies on block copoly(ether-urethane) phase behaviour

Abstract New experimental techniques for the characterisation of the thermal-morphological properties of materials have been developed at Daresbury. Many thermal events, for example, melting endotherms, are signals of changes in morphology covering size scales from the atomic to the microscopic, that isAto μm. There are several advantages in collecting both the wide angle (1 to 20A) and small angle (20 to 1000A) patterns simultaneously, along with the DSC trace, to unambiguously characterise such thermal events. New apparatus has been built at Daresbury, consisting of a modified Linkam DSC hot-stage mounted in a combined SAXS/WAXS camera to carry out such studies. In addition, equipment has been assembled to assess the feasibility of combining FTIR and SAXS/WAXS to study structural changes in various poly(ether urethane)s.

A VME‐based photodiode array system for energy dispersive extended x‐ray absorption fine structure

A VME‐based control and data acquisition system has been constructed for time resolved energy dispersive extended x‐ray absorption fine structure. The system is discussed from initial concept to installation on the Daresbury SRS. The system performance is presented in detail together with examples of test data. Current operational characteristics are a 2‐ms readout time for one scan of 512 pixels, at 16 bits resolution. Accumulation of 65 000 scans in a single frame and a total of 64 frames stored in memory. The system has been designed to run at rates of 0.2 ms per scan and a burst mode allowing 128 single scan frames to be accumulated.

Combined small angle X-ray scattering (SAXS) and Fourier transform infrared (FT-IR) spectroscopy in a time resolved mode using synchrotron radiation

Abstract The simultaneous time resolved study of structure development and reaction kinetics during materials processing is an experimental method which has great potential in developing a deeper understanding of the parameters which govern the formation of various material structures and their final properties. A novel combination of synchrotron radiation small angle X-ray scattering and Fourier transform infrared spectroscopy has been developed, at Daresbury Laboratory, to enable these experiments to be conducted. Successful experiments on a series of model segmented block copoly(urethane)s have been performed and have shown that this combination of techniques is feasible, and has the potential to become a very powerful research tool for a wide variety of research fields.

An instrument for combining x-ray multiple diffraction and x-ray topographic imaging for examining crystal microcrystallography and perfection.

Diffraction imaging using x-ray topography (XRT) and x-ray multiple diffraction (XRMD) provide valuable tools for examining the growth defects in crystals and the distributions from ideal lattice symmetry (microcrystallography). The topographic x-ray multiple diffraction microprobe (TMDM) combines the complementary aspects of both techniques enabling XRT and XRMD studies within the same instrument providing a useful resource for the structural characterization of materials that are not very stable in vacuum and electron beam environments. The design of the TMDM instrument is described together with data taken on GaAs (001) and potassium dihydrogen phosphate (001).