D.J. Peake

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.

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.

Bunch mode specific rate corrections for PILATUS3 detectors

The count rate behaviour of PILATUS3 detectors has been characterized for seven bunch modes at four different synchrotrons. The instant retrigger technology of the PILATUS3 application-specific integrated circuit is found to reduce the dependency of the required rate correction on the synchrotron bunch mode. The improvement of using bunch mode specific rate corrections based on a Monte Carlo simulation is quantified.

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.

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.

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.

FREO 2 : An electricity free oxygen concentrator

The World Health Organization recommends oxygen therapy for children with severe pneumonia, but this essential medicine is unavailable in many health centres in limited-resource settings. To address this need, an appropriate means of oxygen provision will need to be low-cost and robust, require little maintenance and not compete for fuel with other vital functions, and be environmentally sustainable. This report presents the preliminary results of the Fully Renewable Energy Oxygen (FREO2) system, confirming the viability of a novel means of producing medical grade oxygen without any electricity. The approach relies on exploiting the reduction in pressure of water flowing through a raised siphon to create a source of vacuum. This is used to power a customised vacuum-pressure-swing-adsorption system and produce medical grade oxygen. The FREO2 system has been designed to meet the criteria for successful oxygen delivery in small health facilities. It is ideally suited for deployment in tropical or mountainous regions with proximity to flowing water. Importantly, the oxygen generating capacity of FREO2 rises with the increased demand commonly observed during the rainy season in such climates.

Characterisation of an electron collecting CdTe strip sensor using the MYTHEN readout chip

MYTHEN is a single photon counting hybrid strip X-ray detector that has found application in x-ray powder diffraction (XRPD) experiments at synchrotrons worldwide. Originally designed to operate with hole collecting silicon sensors, MYTHEN is suited for detecting X-rays above 5 keV, however many PD beamlines have been designed for energies above 50 keV where silicon sensors have an efficiency of only few percent. In order to adapt MYTHEN to meet these energies the absorption efficiency of the sensor must be substantially increased. Cadmium-Telluride (CdTe) has an absorption efficiency approximately 30 times that of silicon at 50 keV, and is therefore a very promising replacement candidate for silicon. Furthermore, the large dynamic range of the pre-amplifier of MYTHEN and its double polarity capability has enabled the characterisation of an electron collecting Schottky type CdTe sensor. A CdTe MYTHEN system has undergone a series of characterisation experiments including stress test of bias and radiation induced polarizations. The performance of this system will be presented and discussed.

PSIMOD - A generalised system model for investigating the performance of hybrid pixel detectors

Recent advances in hybrid pixel detectors (HPD), motivated by the stringent demands of high-energy-physics experiments, have made a new type of spectroscopically-enabled photon-counting detector feasible. These developments could lead to improved imaging in medical and tomographic applications where detector noise currently imposes limitations. PSIMOD is a generalised system model based on a combination of GEANT4, the TCAD semiconductor simulation package and the SPICE analogue circuit simulation program. It has been developed to reproduce the response of the analogue front end of a pixelated single photon counting detector. With this suite of correlated simulations, it is possible to quickly characterise different system configurations for various detectors.

Time Resolved Detectors and Measurements for Accelerators and Beamlines at the Australian Synchrotron

Time resolved experiments require precision timing equipment and careful configuration of the machine and the beamline. The Australian Synchrotron has a state of the art timing system that allows flexible, real‐time control of the machine and beamline timing parameters to target specific electron bunches. Results from a proof‐of‐principle measurement with a pulsed laser and a streak camera on the optical diagnostic beamline will be presented. The timing system was also used to fast trigger the PILATUS detector on an x‐ray beamline to measure the fill pattern dependent effects of the detector. PILATUS was able to coarsely measure the fill pattern in the storage ring which implies that fill pattern intensity variations need to be corrected for when using the detector in this mode.