M. R. Dimmock

Validation of Pulse Shape Simulations for an AGATA Prototype Detector

An AGATA symmetric, coaxial, high-purity germanium (HPGe) detector has been scanned in coincidence mode. Charge pulse shapes from the 36-fold segmented outer contacts and center contact were stored for events at more than 2000 precisely determined 3-D interaction positions spread over ten depths (z). A database (basis) of the 37 average experimental pulse shapes at each position was generated. The electric field simulation code Multi Geometry Simulation (MGS) was used to generate the pulse shapes for the geometry on a 1.0-mm cubic grid. A minimization between the experimental pulse shapes at each position and the MGS basis yielded mean displacements of between 1.5 and 3.0 mm in the x- y plane. The vectors of these displacements were biased in the direction of the center of the detector. This effect is attributed to cross-talk. The maximum level of derivative cross-talk was measured and shown to be 534%ns. However due to the lack of a global clock in the acquisition system, it could not be accounted for throughout the basis.

Optimization of propagation-based x-ray phase-contrast tomography for breast cancer imaging

The aim of this study was to optimise the experimental protocol and data analysis for in-vivo breast cancer x-ray imaging. Results are presented of the experiment at the SYRMEP beamline of Elettra Synchrotron using the propagation-based phase-contrast mammographic tomography method, which incorporates not only absorption, but also x-ray phase information. In this study the images of breast tissue samples, of a size corresponding to a full human breast, with radiologically acceptable x-ray doses were obtained, and the degree of improvement of the image quality (from the diagnostic point of view) achievable using propagation-based phase-contrast image acquisition protocols with proper incorporation of x-ray phase retrieval into the reconstruction pipeline was investigated. Parameters such as the x-ray energy, sample-to-detector distance and data processing methods were tested, evaluated and optimized with respect to the estimated diagnostic value using a mastectomy sample with a malignant lesion. The results of quantitative evaluation of images were obtained by means of radiological assessment carried out by 13 experienced specialists. A comparative analysis was performed between the x-ray and the histological images of the specimen. The results of the analysis indicate that, within the investigated range of parameters, both the objective image quality characteristics and the subjective radiological scores of propagation-based phase-contrast images of breast tissues monotonically increase with the strength of phase contrast which in turn is directly proportional to the product of the radiation wavelength and the sample-to-detector distance. The outcomes of this study serve to define the practical imaging conditions and the CT reconstruction procedures appropriate for low-dose phase-contrast mammographic imaging of live patients at specially designed synchrotron beamlines.

Characterisation Results From an AGATA Prototype Detector

An Advanced GAmma Tracking Array (AGATA) symmetric prototype high purity Germanium (HPGe) detector has been tested. The detector was illuminated with a 1 mm collimated beam of 137Cs (662 keV) gamma rays. The beam was raster scanned across the front and sides of the detector and the charge sensitive preamplifier output pulse shapes from all 37 channels (36 segments plus the centre contact) were digitised and stored for off-line analysis. Rise time and image charge asymmetry magnitudes were measured as a function of interaction position to study the charge transport properties through the crystal volume. These parameters were then utilised as a calibrated look up table with which in-beam data was analysed and Doppler corrected. An average position resolution of approximately 9 mm (FWHM) was achieved with a crude analysis.

Coulomb shifts and shape changes in the mass 70 region

The technique of recoil {beta} tagging has been developed which allows prompt {gamma} decays in nuclei from excited states to be correlated with electrons from their subsequent short-lived {beta} decay. This technique is ideal for studying nuclei very far from stability and improves in sensitivity for very short-lived decays and for high decay Q-values. The method has allowed excited states in {sup 78}Y to be observed for the first time, as well as an extension in the knowledge of T=1 states in {sup 74}Rb. From this new information it has been possible to compare Coulomb energy differences (CED) between T=1 states in {sup 70}Br/{sup 70}Se, {sup 74}Rb/{sup 74}Kr, and {sup 78}Y/{sup 78}Sr. The A=70 CED exhibit an anomalous behavior which is inconsistent with all other known CED. This behavior may be accounted for qualitatively in terms of small variations in the Coulomb energy arising from shape changes.

Structure of 23Al from the one-proton breakup reaction and astrophysical implications

The ground state of the proton-rich nucleus 23Al has been studied by one-proton removal on a carbon target at about 50 MeV/nucleon using the EXOGAM + SPEG experimental setup at GANIL. Longitudinal momentum distributions of the 22Mg breakup fragments, inclusive and in coincidence with gamma rays de-exciting the residues, were measured. The ground-state structure of 23Al is found to be a configuration mixing of a d-orbital valence proton coupled to four core states - 0

MULECS: The Monash University Low Energy Compton scattering package

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Validation of a Geant4 model of the X-ray fluorescence microprobe at the Australian Synchrotron.

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Towards Optimal Collimator Design for the PEDRO Hybrid Imaging System

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Modeling and simulation of the entire detector system by using Matlab and Simulink

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Design of a prototype hybrid small animal imaging system

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