R.P. Rassool

Improved count rate corrections for highest data quality with PILATUS detectors

A Monte Carlo simulation is presented, which computes the rate correction factors taking into account the detector settings and the time structure of the X-ray beam. The results show good agreement with experimentally determined correction factors.

Micrometre resolution of a charge integrating microstrip detector with single photon sensitivity

The spatial resolution of a single-photon-resolving integrating system has been improved using a non-linear charge interpolation approach. The resolution limit for a 20 µm-pitch sensor is presented.

Success and failure of dead-time models as applied to hybrid pixel detectors in high-flux applications

Detector response functionals are found to have useful but also limited application to synchrotron studies where bunched fills are becoming common. By matching the detector response function to the source temporal structure, substantial improvements in efficiency, count rate and linearity are possible.

Synchrotron radiation hardness studies of PILATUS II

A synchrotron beam has been used to investigate the radiation tolerance of a PILATUS II module. It has been demonstrated that radiation-induced threshold shifts become significant above 30 Mrad. Individual adjustment of pixel thresholds after irradiation enabled retention of standard behaviour in excess of 40 Mrad. This implies that a module can be continuously irradiated for in excess of 40 days at an individual pixel count rate of 10(6) counts s(-1).

Measurements of 10B(γ, p) and 10B(γ, pn) Cross Sections at Eγ=66∼103 MeV

Measurements of the cross sections of 10 B(γ, p) and 10 B(γ, pn) with tagged photons have been performed at E γ =66∼103 MeV. The results of both the 10 B(γ, p) and (γ, pn) measurement show the dominance of a two-nucleon photoabsorption process in this energy region.

Simulating the Counting Mechanism of PILATUS2 and PILATUS3 Detectors for Improved Count Rate Corrections

PILATUS systems are well established as X-ray detectors at most synchrotrons. Their single photon counting capability ensures precise measurements, but introduces a short dead time after each hit, which becomes significant for photon rates above a million per second and pixel. The resulting loss in the number of counted photons can be corrected for by applying corresponding rate correction factors. This article presents a Monte-Carlo simulation, which computes the correction factors taking into account the detector settings as well as the time structure of the X-ray beam at the synchrotron. For the PILATUS2 detector series the simulation shows good agreement with experimentally determined correction factors for various detector settings at different synchrotrons. The application of more accurate rate correction factors will improve the X-ray data quality at high photon fluxes. Furthermore we report on the simulation of the rate correction factors for the new PILATUS3 systems. The successor of the PILATUS2 detector avoids the paralysation of the counter, and allows for measurements up to a rate of ten million photons per second and pixel. For fast detector settings the simulation is capable of reproducing the data within one to two percent at an incoming photon rate of one million per second and pixel.

Defect Structures in Diamond Composite Coated Cemented Tungsten CarbideSubstrates

Variability in the abrasive wear of PCD coatings on cemented WC substrates has been investigated. Six samples of PCD coated carbides were tested in a wear testing rig. The PCD coated element was used to turn an industry standard vitrified bonded corundum grinding wheel. The wear rate was measured as the weight loss of the cutting element per cubic metre of grinding wheel machined during the test. Two grades of cutting elements were observed. One grade had wear rates between 6 and 7.3 g/m³ but of the three poor quality samples, only one valid test was made realising wear rate of ~7,800 g/m³. The microstructures of the samples were studied using SEM, X-ray imaging, neutron diffraction and XRD. SEM images revealed differences in the volume percentage of diamonds in the two grades and the XRD scans highlighted the variable distribution of the diamond phase in the coating. Estimates of the residual stresses in a good and poor quality samples indicated significantly higher compressive stresses in the good quality versus poor quality coating. These results have revealed two extremes in the wear rates of these PCD coated carbides. It is suggested that the difference in diamond content between the two grades is not sufficient to account for the 3 orders-of-magnitude difference in the observed wear rates. However, the presence of intrusive veins of carbide material in the coatings, especially around the curved cutting tip, suggested that the macroscopic defects observed in the x-ray and SEM images were the major cause of the high wear rates in the poor quality sample.

Preliminary studies for top-up operations at the Australian Synchrotron

The Australian Synchrotron is now a fully commissioned synchrotron light source providing beam for users [1]. With the facility now fully operational, the next major advancement in machine operations will be top-up mode. The advantages of running in a dynamic top-up mode are well documented by other third generation light sources (see for examples references [2, 3, 4]) ; in broad terms it leads to a better quality beam for some users, and better experimental results. An overview will be given of the top-up runs that have been conducted and the instrumentation that was used. It has been demonstrated that top-up operation is possible, however improvements in injection efficiency and beam stability during injection are required before this can become a routine mode of operation.

The Current Status of a Non-Invasive Arterial Monitor under Development

A non-invasive arterial monitor (NIAM) is being developed as an alternative to invasive arterial sampling to measure the input function of radiotracer uptake in PET patients. NIAM consists of dual Bismuth Germanate (BGO)-block detectors. The output was digitized at 500 MHz, and then processed to generate energy, timing and position information. System matrices were calculated for a range of geometries, allowing iterative reconstruction of tomographic images. Countrate efficiency was measured as 4.8cps/(kBq/ml) and countrate linearity was confirmed up to 330kBq/ml. The coincidence time resolution was measured using two techniques; a digital Constant Fraction Discriminator (CFD) and a Parametric Waveform Analysis (PWA). The resulting time-resolutions were; tCFD = 7.8ns and tPWA = 5.7ns. Spatial resolution was measured, both parallel (Deltax,y) and orthogonal (Deltaz) to the detector faces. At 140mm block separation, the measured resolution was Deltax,y = 6mm and Deltaz = 21mm. The system was simulated using the Geant4 Application for Tomographic Emission (GATE) to compare measured- vs. simulated-performance. After the dual-block validation of GATE, the performance characteristics of a simulated quad-block system were investigated.

A Low-Pressure Oxygen Storage System for Oxygen Supply in Low-Resource Settings

BACKGROUND: Widespread access to medical oxygen would reduce global pneumonia mortality. Oxygen concentrators are one proposed solution, but they have limitations, in particular vulnerability to electricity fluctuations and failure during blackouts. The low-pressure oxygen storage system addresses these limitations in low-resource settings. This study reports testing of the system in Melbourne, Australia, and nonclinical field testing in Mbarara, Uganda. METHODS: The system included a power-conditioning unit, a standard oxygen concentrator, and an oxygen store. In Melbourne, pressure and flows were monitored during cycles of filling/emptying, with forced voltage fluctuations. The bladders were tested by increasing pressure until they ruptured. In Mbarara, the system was tested by accelerated cycles of filling/emptying and then run on grid power for 30 d. RESULTS: The low-pressure oxygen storage system performed well, including sustaining a pressure approximately twice the standard working pressure before rupture of the outer bag. Flow of 1.2 L/min was continuously maintained to a simulated patient during 30 d on grid power, despite power failures totaling 2.9% of the total time, with durations of 1–176 min (mean 36.2, median 18.5). CONCLUSIONS: The low-pressure oxygen storage system was robust and durable, with accelerated testing equivalent to at least 2 y of operation revealing no visible signs of imminent failure. Despite power cuts, the system continuously provided oxygen, equivalent to the treatment of one child, for 30 d under typical power conditions for sub-Saharan Africa. The low-pressure oxygen storage system is ready for clinical field trials.