J.E Bateman

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.

Performance characterisation of large area BaF2-TMAE detectors for use in a whole body clinical PET camera

The first of two large area detectors which form part of a new whole body positron scanner has been fully characterised and a performance assessment has been completed. The detector consists of an array of crystals coupled to a large area, low pressure multiwire chamber filled with tetrakis-(dimethylamino)-ethylene (TMAE) gas. A complete optimisation has been carried out in the operation of the chamber in order to establish optimal levels of stability and performance. Under the optimised operational conditions the detector exhibits an efficiency of ∼ 25%, with a time and position resolution of 3.5 ns (FWHM) and 6.5 mm (FWHM) respectively. A Monte Carlo simulation of the complete dual headed PET camera has been used to assess the expected image quality in terms of contrast and signal to noise ratio. The simulation has been also used to establish the effect of utilising crystal slabs and a support frame to cover the active area of each detector in comparison with a single sheet of BaF2. The results demonstrate that the use of crystal tiles results in a small increase in the background noise, not significantly compromising the image quality.

Energy resolution in X-ray detecting micro-strip gas counters

Abstract Systematic measurements of the energy resolution available from a Micro-Strip Gas Counter (MSGC) are presented. The effect of factors such as bias potential, gas filling and strip geometry on the energy resolution are examined in detail and related to a simple model. The geometry of the MSGC is adapted to permit “wall-less” detection of X-rays and this results in useful improvements in the pulse height spectra.

THE PIN PIXEL DETECTOR - NEUTRON IMAGING

The development and testing of a neutron gas pixel detector intended for application in neutron diffraction studies is reported. Using standard electrical connector pins as point anodes, the detector is based on a commercial 100 pin connector block. A prototype detector of aperture 25.4mm x 25.4mm has been fabricated, giving a pixel size of 2.54mm which matches well to the spatial resolution typically required in a neutron diffractometer. A 2-dimensional resistive divide readout system has been adapted to permit the imaging properties of the detector to be explored in advance of true pixel readout electronics. The timing properties of the device match well to the requirements of the ISIS pulsed neutron source.

Precision measurement of X-ray line spectra by energy dispersion in a gas microstrip detector

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.

Enhancement of X-ray line energy spectra from a gas microstrip detector

Abstract It is shown that the stable line response function produced by a gas microstrip detector operated in “wall-less” mode permits mathematical manipulation, which greatly facilitates analysis of the data and explicit enhancement of X-ray line spectra. As a result, given adequate counting statistics, effective energy resolution comparable to that of a cryogenic silicon or germanium detector may be achieved.

Count rate performance and deadtime analysis of the new 3D PETRRA PET Camera

We report on the count-rate performance of the unique PETRRA positron camera at activities up to 60MBq. The camera consists of two large area detectors, each comprising a tiled array of 10mm thick BaF2 scintillation crystals interfaced to a multi-step avalanche chamber filled with 4.2mbar of pure TMAE vapor. Preliminary results demonstrate coincident count rates of over 80kcps for a cylindrical (20x20cm3) phantom with 50MBq of F-18 in the field-of-view using a 20ns coincidence time window. Each component of the readout cycle has been characterized in terms of dead-time loss. The cameras dead-time related count loss is well-described by a paralysable model with a dead-time of ~500ns. Other sources of count rate loss are also discussed.