The development and testing of the Off Specular MicrOstrip Neutron Detector (OSMOND) is described. Based on a microstrip gas chamber the aim of the project was to produce a high counting rate detector capable of replacing the existing rate limited scintillator detectors currently in use on the CRISP reflectometer for off specular reflectometry experiments. The detector system is described together with results of neutron beam tests carried out at the ISIS spallation neutron source.

The development and testing of the FastGas neutron detector is described. Based on a Gas Microstrip Chamber the aim of the project was to produce a high counting rate detector capable of replacing the existing 3He tubes for specular reflectometry, currently in use on the ISIS reflectometer instruments. The detector system is described together with results of neutron beam tests carried out at the ISIS spallation neutron source.

The advent of the microstrip gas chamber (MSGC) has permitted the development of position-sensitive gas avalanche detectors, which combine sub-millimeter spatial resolution with multi-MHz global rate capabilities not attainable with traditional types of gas counters. Based on massively parallel electronic readout, the need to keep down electronic channel costs imposes a simple front-end design without in-built deadtime compensation. In this report we show that insitu calibration of the deadtime of the detector system is straight-forward and reliable. Methods are described for applications to X-ray and neutron detection.

The high overall throughput wide angle X-ray scattering (HOTWAXS) gas detector system, aimed at X-ray diffraction (XRD) and wide angle X-ray scattering (WAXS) applications has been a successful user facility on stations 2.1 and 9.3 at the Daresbury SRS offering high-speed data acquisition. The facility has been duplicated on station I22 of the Diamond light source. The energy range covered by stations I22 and 9.3 is very similar varying from 6 to 30keV, well above the energy range conventionally covered by gas detectors. Here, we report studies of the options for successful operation of HOTWAXS at the upper end of this energy range, made possible by this particular design.

Over the past 10 years combined techniques such as small angle and wide angle X-ray scattering (SAXS/WAXS) and X-ray absorption spectroscopy (XAS) with X-ray diffraction (XRD), have become the mainstay of time resolved experimental studies carried out at synchrotron radiation sources (SRS). However, these techniques have been limited by the detectors used to measure the wide angle scattering/diffraction pattern, and therefore restrict the dynamic experiments that can be studied. The HOTWAXS (high overall throughput wide-angle X-ray scattering) detector project was designed to address this issue by producing a position sensitive, parallax free, high count rate, photon counting detector based on microstrip gas chamber (MSGC) technology. The initial experiments, performed on station 16.1 of the Daresbury SRS, with a high density polyethylene sample, confirmed the local count rate per channel to be 1times106 counts per second. A global count rate over the 512 channel detector of 27times106 counts per second was also measured for this sample. Time resolved experiments on stations 2.1 and 9.3 with real 'user' samples have also been performed, the results of which are presented.

The development and testing of the HOTWAXS position-sensitive X-ray detector for Synchrotron Radiation Sources is described. Funded from a facility development grant, the aim of the project was to produce a high counting rate, parallax-free photon counting detector to be used in the combined studies of X-ray absorption fine structure and X-ray diffraction (XAFS/XRD), and also in the technique of small angle and wide angle X-ray scattering (SAXS/WAXS). The detector system is described together with results of experiments carried out at the Daresbury Laboratory Synchrotron Radiation Source.

The development and testing of a two-dimensional (2-D) prototype detector based on a microstrip gas chamber (MSGC) is reported using a gas mixture of 2.5 bar /sup 3/He and 2.5 bar CF/sub 4/. The second coordinate is obtained by utilising a plane of wires as pick up electrodes. The detector is operated with the wire plane at such a potential so as not to induce any gain around the wires. This means that the high tolerances normally associated with wire planes in multi wire proportional counters are not mandatory. The detector comprises of 48 individually instrumented channels in both X (MSGC strips) and Y (orthogonal wire plane). A specially designed encoding module has been constructed which feeds digital addresses for each event to the ISIS Data Acquisition Electronics (DAE) system. An intrinsic detector resolution of /spl sim/1 mm full-width at half-maximum has been measured for both dimensions (in experimental exposures on the ROTAX beamline at ISIS) which is degraded slightly by the digital resolution for the overall system. This readout method is shown to be very tolerant of a poor signal to noise ratio in the readout channels (unlike traditional analogue wire chamber readout systems) and permits the operation of the MSGC at low avalanche gains (/spl sim/10) which helps to maximize the rate and lifetime performance of the detector as well as permitting data capture rates in the megahertz range. The event timing resolution is comfortably submicrosecond and is, therefore, suitable for applications on spallation neutron sources.

This report describes development work in which systematic changes in the electrode pattern of a gas microstrip detector are explored in the search for higher avalanche gains and enhanced stability. It is found that the width of the cathode structure is the main determinant of the detector stability. With the correct cathode width, gas gains of >50 000 are comfortably attainable with low detector noise so that X-rays can potentially be detected down to the limit of a single X-ray produced photoelectron.

The PETRRA positron camera is a large-area (600 mm x 400 mm sensitive area) prototype system that has been developed through a collaboration between the Rutherford Appleton Laboratory and the Institute of Cancer Research/Royal Marsden Hospital. The camera uses novel technology involving the coupling of 10 mm thick barium fluoride scintillating crystals to multi-wire proportional chambers filled with a photosensitive gas. The performance of the camera is reported here and shows that the present system has a 3D spatial resolution of approximately 7.5 mm full-width-half-maximum (FWHM), a timing resolution of approximately 3.5 ns (FWHM), a total coincidence count-rate performance of at least 80-90 kcps and a randoms-corrected sensitivity of approximately 8-10 kcps kBq(-1) ml. For an average concentration of 3 kBq ml(-1) as expected in a patient it is shown that, for the present prototype, approximately 20% of the data would be true events. The count-rate performance is presently limited by the obsolete off-camera read-out electronics and computer system and the sensitivity by the use of thin (10 mm thick) crystals. The prototype camera has limited scatter rejection and no intrinsic shielding and is, therefore, susceptible to high levels of scatter and out-of-field activity when imaging patients. All these factors are being addressed to improve the performance of the camera. The large axial field-of-view of 400 mm makes the camera ideally suited to whole-body PET imaging. We present examples of preliminary clinical images taken with the prototype camera. Overall, the results show the potential for this alternative technology justifying further development.

The development and testing of a 2-D prototype detector based on a gas microstrip detector (GMSD) is reported using a gas mixture of 2.5 bar /sup 3/He and 2.5 bar CF/sub 4/. The second coordinate is obtained by utilising a plane of wires as pick up electrodes. The detector is operated with the wire plane at such a potential so as not to induce any gain around the wires. This means that the high tolerances normally associated with wire planes in multi wire proportional counters are not mandatory. The detector comprises of 48 individually instrumented channels in both X (GMSD strips) and Y (transverse wire plane). A specially designed encoding module has been constructed which feeds digital addresses for each event to the ISIS data taking electronics system (DAE). An intrinsic detector resolution of /spl sim/1 mm FWHM has been measured for both dimensions (in experimental exposures on the ROTAX beamline at ISIS) which is degraded slightly by the digital resolution for the overall system. This readout method is shown to be very tolerant of a poor signal to noise ratio in the readout channels (unlike traditional analogue wire chamber readout systems) and permits the operation of the GMSD at low avalanche gains (/spl sim/10) which helps to maximise the rate and lifetime performance of the detector as well as permitting data capture rates in the MHz range. The event timing resolution is comfortably sub microsecond and is therefore suitable for applications on spallation neutron sources.

The ability to perform X-ray absorption spectroscopy (XAS) in the 300 - 1500 eV energy range allows measurements to be made on transition metal compounds. This paper describes a detector and the technique used to perform fluorescent measurements on such materials. A variety of test sample results are shown to illustrate the low energy and energy-resolving capabilities of the detector ( based on gas microstrip technology). Two possible applications are also demonstrated. The first shows how the detector can be used to gather X-ray absorption spectra for the L edges of transition metals and K edges of light elements ( C, O and N). The other shows how the magnetic immunity of the detector can be exploited to study the magnetic properties of materials.

A simple, general parametric model of the avalanche process in gas counters is described. Applicable to all the common forms of gas avalanche detector—wire, microstrip, point anode and parallel gap, the model describes the gain process in terms of two pseudo-physical constants which are effectively invariant over the working range of any given detector configuration. For counter operation over a wide range of conditions (e.g. very different gas pressures) the model is extended so that four parameters are required to model the gain. Applications of the model to the characterisation, operation and design of a variety of counter types are given.

This study describes development work in which systematic changes in the pitch of the electrode pattern of a Microstrip Gas Counter (MSGC) are explored in the search for higher gas gains and enhanced stability. We investigated the gas gain, soft X-ray energy resolution and the detector noise with pitch values set between 300 μm and 1200 μm. With the cathode width set to half of the pitch and anode width at 5 μm, gas gains exceeding 50,000 were comfortably achieved. We present the optimised MSGC geometry which permits radiation detection in the sub-keV X-ray region.

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.

The results are presented of a development programme aimed at the validation of the key concepts and technologies for the construction of a two-dimensional X-ray detector based on gas microstrip detector technology using resistive division along the anode to achieve the second dimension. A prototype detector and its associated electronic readout system have been developed which demonstrate the capability of a spatial resolution (standard deviation) of approximately 11000 of the working aperture combined with readout rates of up to 400kHz per anode. Test results and a description of the position sensing circuitry are given.

The development and testing of a soft X-ray gas pixel detector, which uses connector pins for the anodes is reported. Based on a commercial 100 pin connector block, a prototype detector of aperture 25.4mm x 25.4mm can be economically fabricated. The individual pin anodes all show the expected characteristics of small gas detectors capable of counting rates reaching I MHz per pin. A 2-dimensional resistive divide readout system has been developed to permit the imaging properties of the detector to be explored in advance of true pixel readout electronics. (C) 2002 Elsevier Science B.V. All rights reserved.

It is shown that when a gas microstrip detector (GMSD) is operated in such a way as to gain freedom from detector wall effects, the response of the detector to an X-ray line is stable and can be fitted reliably with a lognormal (LN) distribution function. The LN function permits the fitting of adjacent, overlapping X-ray lines with an accuracy in position of a few eV with an attendant penalty in the statistics required for a given precision in the amplitude measurement. Experimental data and Monte Carlo simulation data are presented to indicate the possible range of usefulness of this technique for energy-dependent X-ray line spectroscopy in applications (such as X-ray fluorescence analysis). The usefulness of the LN fits for detector studies is also noted.

The gas microstrip detector (GMSD) makes an excellent planar (position sensitive) amplifier of incident electron clouds because both the anodic and cathodic gain-defining elements are produced lithographically on the same rigid substrate. We have studied the dependence of the gas gain and pulse height resolution of the plate as a function of various geometric and gas parameters. The results show that a GMSD can be made very insensitive to the shape of the drift electrode, allowing it to be used in a wide variety of applications. An example of an electron-yield XAFS study is given. The aim of this work is to produce a well defined technology platform from which to build detectors that meet the requirements of high flux synchrotron radiation and neutron facilities, both of which are key CLRC facilities.

Extended X-ray absorption fine structure (EXAFS) studies are a powerful technique for studying the chemical environment of specific atoms in a molecular or solid matrix. The study of the surface layers of “thick” materials introduces special problems due to the different escape depths of the various primary and secondary emission products which follow X-ray absorption. The processes are governed by the properties of the emitted fluorescent photons or electrons and of the material. Their interactions can easily destroy the linear relation between the detected signal and the absorption cross-section. Also affected are the probe depth within the surface and the background superimposed on the detected emission signal. A general mathematical model of the escape processes is developed which permits the optimisation of the detection modality (X-rays or electrons) and the experimental variables to suit the composition of any given surface under study.