G.R. Mant

Simultaneous time resolved SAXS and WAXS experiments using synchrotron radiation

Abstract Instrumentation has been developed which offers the possibility of performing simultaneous time resolved small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) experiments in the range from approximately 0.007–0.21 A −1 and 0.31–4.2 A −1 . A synchrotron SAXS beamline is therefore equipped with two gas filled proportional detectors. The ultimate system time resolution will be of the order of 1 μs. Successful test experiments have been performed on block copolymer samples and polyethylene.

Simultaneous SAXS/WAXS and d.s.c. analysis of the melting and recrystallization behaviour of quenched polypropylene

Abstract The behaviour of a quenched ethylene-propylene block copolymer cast film has been investigated during melting and recrystallization experiments carried out at heating and cooling rates of 10°;C min −1 . The experimental techniques used to follow the melting and recrystallization processes were differential scanning calorimetry (d.s.c.) and simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). In particular, the WAXS results show that the melting of the material is preceded by a solid-state transition involving transformation of the quenched structure into the monoclinic α modification. This transition appears as an exotherm in the range 65–120°C on the d.s.c. melting trace. SAXS results show that an increase in the amount of long-range order occurs during this transition. The sample was then found to melt at 162°C. Upon cooling from the melt, recrystallization of the monoclinic α modification was found to occur in the range 123-105°C without any apparent prior formation of the quenched structure.

A direct method to determine the degree of crystallinity and lamellar thickness of polymers: application to polyethylene☆

Abstract Time-resolved small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) patterns have been simultaneously obtained during melting and crystallization of high-density polyethylene using a newly constructed camera at the SRS, Daresbury. The data have been analysed to yield the long spacing, the degree of crystallinity and the lamellar thickness in the context of the two-phase model. The long spacing was obtained from the peak in the Lorentz-corrected SAXS pattern. The degree of crystallinity was obtained from a combination of the SAXS invariant and the integrated WAXS intensity of the crystals. The invariant passes through a maximum at 50% crystallinity and the integrated WAXS intensity is a minimum for the melt. Thus two points in the linear relationship between the WAXS intensity and the degree of crystallinity are known, affording calibration. Calculation of the degree of crystallinity by solving the quadratic in the SAXS invariant gave good agreement with the WAXS result. The long spacing and the degree of crystallinity may be combined in the two-phase model to estimate the lamellar thickness, an important parameter in determining mechanical properties.

Multiwire X-ray detector systems at the daresbury srs

Abstract Synchrotron radiation allows the study of structural dynamics by X-ray diffraction techniques. These experiments impose unusual demands on X-ray detector systems. High count rates, wide dynamic range, good spatial and temporal resolution and real time data processing are all required. A recently completed system fulfills many of these requirements having a spatial resolution of better than 0.3 × 0.3 mm over an area of 200 × 200 mm with a 600 kHz throughput and a dynamic range limited by counting statistics. Examples derived from the existing experimental programme are used to illustrate the performance of these devices.

The application of multiwire x-ray detectors to experiments using synchrotron radiation

Multiwire detectors have certain characteristics that can be used to advantage, particularly in small-angle diffraction or scattering experiments on biological systems. The size of the active region of the detector and the total number of pixels can be conveniently matched to the dimensions of the synchrotron beam and to the optics of the beam line camera. Furthermore, the large dynamic range inherent in single-photon counting systems can be exploited to ensure the collection of high-quality data even when the scattering factor varies over several orders of magnitude. Linear and two-dimensional detectors are in regular use at the Daresbury Synchrotron Radiation Source, all using the delay-line readout method and a standardised data acquisition system which includes facilities for time-resolved measurements. The development of a new system (now at the prototype stage) to operate at the very high count rates available from synchrotron sources is outlined in this paper.

The Application Of Multiwire Proportional Counters To Experiments Utilising Synchrotron Radiation

Although multiwire detectors have been overtaken in some applications of x-ray imaging, they have certain characteristics which can be used to advantage in synchrotron radiation studies, for example in small angle diffraction or scattering experiments on biological systems.In particular,the size of the active region of the detector and the total number of pixels can be conveniently matched to the dimensions of the synchrotron beam and to the optics of the beam line camera.Furthermore,the large dynamic range inherent in single photon counting systems can be exploited to ensure the collection of high quality data even when the diffuse and coherent scattering factor varies over several orders of magnitude. Linear and two dimensional detectors are in regular use at the Daresbury Synchrotron Radiation Source all using the delay line readout method and a standardised data acquisition system which includes facilities for time resolved measurements. The source characteristics and the beam line optical instrumentation are described to show the properties which influence the design of imaging detectors and from this the parameters of the detectors currently in use are examined together with details of test measurements. Some examples of experimental results are given. The development of systems for one and two dimensional detectors to replace the delay line readout method and to operate at the very high count rates available from synchrotron sources is being actively pursued and will soon reach prototype stage.The design of these systems which use custom designed circuits and high speed digital correlation techniques will be outlined.

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.

Multiple simultaneous time‐resolved experimental techniques

The desire to eliminate experimental artifacts due to the correlation of several independent time‐resolved experiments has provided the impetus to attempt to perform several simultaneous experimental techniques on a single sample. The data acquisition system of an existing small angle x‐ray scattering beam line has been adapted in order to accommodate the simultaneous operation of a second detector system in order to collect the wide angle x‐ray scattering pattern. Electronic pulses received and/or generated by the data acquisition system enable control and communication with PC’s controlling the sample environment.

A multiwire linear X-ray detector and data acquisition system for the Daresbury SRS

Abstract An X-ray detecting system for time resolved X-ray diffraction is described. The front end of the system is a multiwire proportional chamber. Priority encoding techniques are used to encode the position of the X-ray quanta. The system includes facilities for fast time slicing and simultaneous collection of calibration information.

Radiation damage to free adenosine triphosphate and guanine molecules by monochromatic x rays

A summary description of the equipment for time‐of‐flight (TOF) mass spectroscopy and its uses in the x‐ray region for the study of radiation damage (photofragmentation) of biologically relevant molecules is given. The technique is illustrated with some recent x‐ray (∼8.1 keV) TOF results obtained from free adenosine triphosphate and guanine molecules. The well defined time structure of synchrotron radiation has been employed in order to record the molecular decomposition in real time. It has, thereby, been possible to determine which bonds are most susceptible to bond breakage following irradiation of the molecules by x rays.