Dissertations / Theses on the topic 'Proton-induced X-ray emission'

The capabilities of the equipment for proton induced X-ray emission analysis at the University of Surrey were examined with particular reference to the trace element analysis of biological samples. The study of samples arising from the Guildford Breast Screening Project was continued. The requirements for trace element analysis of biological samples are outlined together with a review of the available physical analysis techniques. Detail is given of the factors to be considered in order to establish that the study of elemental concentrations by PIXE is feasible. The apparatus used for PIXE analysis is described in detail together with recent improvements to the equipment. The development of a spectrum analysis code HISTO, which simulates the processes of manual analysis, was undertaken. The performance of the code was compared favorably to that of the Ge(Li) spectrum analysis code SAMPO. A preliminary study of 20 samples of human breast cyst fluid was undertaken. The minimum detection limits for those elements assayed by comparative analysis were calculated. The methodology of sample preparation was improved after the examination of target homogeneity and contamination. During a more detailed study of 30 samples the concentration of 9 elements relative to the concetration of potassium was calculated. Calculation of the minimum recommended sample size for elements with Z ≥ 26 indicated that a much larger sample size would be required for reliable results. The PIXE microprobe facility is described and the alignment and operation procedures are outlined. The microprobe was used to examine tree ring samples; examples of some 1D scans are presented. Recommendation that the spectrum analysis code is developed to include a peak location capability is made. Progress with the breast cyst fluid analysis programme is reviewed. The requirement to improve the proton beam current measurment equipment and the data analysis facilities is noted.

Thesis (M.Sc.)(Hons) -- University of Western Sydney, 2005.
"A thesis presented to the University of Western Sydney in fulfilment of the requirements for the degree of Master of Science (Honours) Physics" Bibliography: leaves 101-108.

Proton induced x-ray emission spectroscopy (PIXE) is a rapid and sensitive analytical technique for the non-destructive simultaneous determination of elemental concentrations above atomic number 11 (sodium) and is the only analytical technique that can determine 20-30 elements nondestructively in a single small sample (≈5 mg) with detection limits of 1- 5 ppm (dry weight). Part I of this dissertation outlines work done on the optimization of instrumental parameters and sample preparation for the analysis of biological tissue. Cultured rabbit renal slices were used as the biological system to demonstrate the use of PIXE analysis. The renal slices were exposed to HgCl₂, CdCl₂, K₂Cr₂0₇, or NaAsO₂ alone or in a mixture. The analysis of biological samples by PIXE provides information on inter-elemental interactions in tissue and body fluids. A computer program for spectrum processing and quantitation, which decomposes overlapped peaks, corrects for thick target matrix effects and calculates results without resorting to the use of standards, is explored. In part II of this dissertation, a convenient method of removing solvent from a benzene extract of graphitic soot containing fullerenes using sublimation, is outlined. Separation of macroscopic quantities of the fullerenes C₆₀ and C₇₀ has been accomplished using a combination of selective precipitation of C₆₀ and chromatography. C₆₀ is selectively crystallized by freezing and thawing a benzene solution of mixed fullerenes, then using the C₇₀ enriched supernatant as starting material in the chromatographic separation of C₆₀ and C₇₀. In the separation scheme, a bed of modified silica sorbent is charged with the fullerene mixture and the fullerenes are eluted using a hexanes/THF mobile phase. The methods of uv-Visible and infrared spectroscopy, as well as high performance liquid chromatography (HPLC) are evaluated for their ability to determine the purity of a C₆₀ or C₇₀ sample.

Trace elements within biological tissues are heterogeneously distributed. This complicates the task of deriving concentrations that represent an organ or specimen as a whole. The derivation of representative concentrations is important in the investigation of tissue health status or exposure to the individual from occupational or man-made pollution sources. Therefore, a knowledge of the elemental dispersions in biological tissues is required. Proton induced X-ray emission (PIXE) analysis is employed in the study of the elemental heterogeneity of porcine liver, kidney, heart and lung. Specimens are analysed in two different modes. One method involves the extraction of sub-samples that are dried, homogenised and manufactured into thick target pellets. This approach however limits the spatial resolution on which elemental distributions may be derived and hence thick specimen sections that can be irradiated directly may be preferred. This type of target though suffers in that surfaces are irregular and proton irradiation and X-ray take-off angles are ill defined. The effect of these surface imperfections upon X-ray yield in PIXE are investigated by the development of simple stylised models. The physical parameters of these models are varied and the elements most affected and dominant factors in modifying X-ray yield are identified. The trace element content for like tissues between targets in the form of pellets and freeze-dried sections are compared and mostly excellent correlation is found. The analysis of specimens in either of these modes stresses the high elemental inhomogeneity of biological samples. A quantitative determination of this elemental heterogeneity is made by the derivation of sampling factors, the minimum mass of material required to reduce elemental variations to a given level of precision. Those sampling factors derived by utilising the data from pelletised targets agree well with the limited values from the literature, whereas a large difference is found for those calculated from thick specimen target sections. This disagreement is thought to be due to the failure of sampling factor theory at the small sampling mass employed in the analysis of the latter targets. Photon transmission tomography was investigated for the ability of the technique to provide a measure of biological specimen heterogeneity, differentiate between different composite tissues and identify regions of interest. This may prove useful for the selection of sub-samples for subsequent trace element analysis. Biological specimens were scanned in fresh and dry states to ascertain the most favourable sample preparation technique to best achieve the above aims, the dry sample states were preferred. Freeze-dried specimens are imaged under differing scanning parameters and their data compared to theoretical values derived from PIXE and Rutherford backscattering (RBS) analysis. Good agreement is found. Regions of interest may be identified in tomographs, this being due to density variations rather than elemental variations, tissues of similar but different composition not being differentiatable due to image noise which is a product of finite counts in reconstructed images. However, with the improvement of photon counting statistics in images, these tissues may be more discernible from one another in tomographs thus making photon transmission tomography a viable technique for the selection of representative sub-samples for subsequent elemental analysis.

Diabetes is one of the fastest growing diseases today, affecting over a million people in the UK. Numerous medical complications, such as heart disease, are regularly associated with diabetes. Despite advances in methods of diagnosis and treatment there is still a need for greater understanding of these diseases. This will include research directed towards the influence of specific treatments and reasons for the high incidence of diabetes and heart disease in 'at risk' populations. Changes in elemental status are associated as the cause or effect of various diseased states. Elemental imbalance in diabetics can result in impaired glucose tolerance and insulin resistance and in sufferers of heart disease elemental changes impair heart rate and elasticity of blood vessels. In the UK 10,000 patients with Ischaemic Heart Disease undergo coronary artery bypass grafting (CABG) surgery each year. Elemental analysis has been carried out on blood samples collected from a group of patients admitted to hospital for bypass surgery. Proton Induced X-ray Emission (PIXE) and Instrumental Neutron Activation Analysis (INAA) have been applied as complementary analytical tools for determining elemental concentrations. Differences have been examined between CABG patients with and without diabetes. Both experimental methods have been used to investigate elemental levels in whole blood, erythrocytes and plasma. Elemental concentration varied according to the blood constituent and reflected short and long-term influences on elemental homeostasis. Plasma was found to concentrate Na, Mg and Ca the highest using both experimental techniques. All blood samples were collected and prepared at St. George's Hospital, Tooting in the UK. An additional study was conducted to investigate the influence of the bypass operation on the patient's elemental status. Whole blood was obtained at pre (1h before operation), post (1-2 hours after operation) and recovery (24 hours after completion of the operation) stages of bypass surgery. Differences between the three phases were observed, individual variations have been plotted so rates of change can be seen and evaluated with the particular medical history. Concentrations of Na, Mg, Al, P, S, Cl, K, Ca and Fe in whole blood were determined. The two measurement techniques found different concentrations however results showed a general trend that post operative concentrations were elevated compared to pre operative values. Analysis of blood drawn during the recovery phase, 24 hours after the surgery, found that concentration were typically approaching pre operative levels. Both PIXE and INAA found concentrations of Na, Mg and Al peaked post operation and then decreased in the recovery phase, towards values measured pre surgery. Various factors may be responsible for the elemental changes occurring during surgery including, hormone production, routine administration of intra-operative fluids and contact of blood with non- endothelial surfaces. Hierarchical cluster analysis has been used to confirm differences between elemental levels in pre, post and recovery stages of bypass surgery. The dendograms produced indicate significant distinction between the three stages. The explosive impact of diabetes in the UK resident Asian population is discussed and the influence of diabetogenic agents introduced. Examination of research literature revealed that betel nut has been implicated as a causative agent in several medical conditions. Samples of Betel nut and six associated chewing materials widely used in Asian communities has been collected and prepared for analysis. Instrumental neutron activation analysis has been used to determine the concentration of Na, Mg, Al, Cl, Ca, V, Mn, Cu and Br in the samples by means of short-lived radionuclides.

Hypertrophic scars are painful and unsightly scars frequently resulting from dermal trauma and characterised by excessive collagen. The application of silicone gel sheeting is an effective treatment for these scars. Proton Induced X-Ray Emission, Elastic (Non-Rutherford) Backscattering and Instrumental Neutron Activation were used to determine the compositional changes in the silicone gel sheeting and the skin resulting from contact of the gel with scarred and unscarred skin, and found that although in vitro tests on split skin and in vivo tests using unscarred tissue causes the skin to absorb Si (an essential constituent of collagen) from the silicone gel sheeting; in vivo tests on hypertrophic scar and control tissue show the reverse: silicone gel sheeting absorbs Si from hypertrophic scars against the concentration gradient. It is believed that this is an important factor in the success of the treatment of hypertrophic scars by silicone gel sheeting. The major, minor and trace element composition was determined for a total of 35 skin samples including breast, abdominal and hypertrophic scar tissue, comparing dermis and epidermis for these samples. Some split skin samples were also included. The hypertrophic scar tissue is characterised by enhanced Si content, with 3wt% compared with an average of 2wt% for the unscarred tissue. A pilot clinical trial was then conducted on 20 unscarred volunteers as controls over a week, and 9 volunteers with hypertrophic scars (clinical gel) over a three month period with silicone gel sheeting nominally used according to a strict protocol. Two subjects did not complete the trial, and there was evidence of non-compliance for at least three others. However, without excluding any data, we have observed a significant increase (10+/-1%) in Si content of the silicone gel sheeting in contact with hypertrophic scar over the controls. Significant composition differences between the dermis and the epidermis were observed as expected. Differences between the composition of scarred and unscarred tissue were not large. Significant increases in the average elemental composition were seen between the clinical gel compared to the unused gel for the elements: Cl, K, Ca, Fe and Ag providing further evidence that the gel absorbs elements from the scar tissue.

A novel experimental set-up was installed at the University of Surrey Ion Beam Centre for the purpose of producing 3D quantitative elemental maps of biological samples by combining simultaneous Proton Induced X-Ray Emission Tomography (PIXE- T), on/off-Axis Scanning Transmission Ion Microscopy-Tomography (STIM-T) and Rutherford Backscatter Spectrometry (RBS). A tomographic sample holder was designed and built and a scattering system developed for On/Off-Axis STIM. 2D PIXE and off-STIM analysis of leukocytes was performed to complement concurrent research and to identify problems with the very recently installed proton microbeam at the Ion Beam Centre. The other major aim was to see if a leukocyte would be a suitable sample for tomographic analysis and to study the damage induced by the beam on biological samples. Instrumental Neutron Activation Analysis (INAA) was performed on hair samples collected from MSc students at the University of Surrey and a database compiled of all elemental analysis of hair performed at the University. This complemented the tomographic analysis performed on a section of a strand of hair. Si, S, Cl, K, Ca, Fe and Zn were mapped using simultaneous PIXE-T, On/Off- Axis STIM-T and RBS.

Proton therapy is one of the most advanced modalities for cancer treatments based on radiation, offering finite penetration depth, low energy deposition at the entrance and sharp dose fall-off. However some of its benefits may become a risk for the patient due to the uncertainties during treatment planning and dose delivery. This project investigates the feasibility of implementing a tool for the real time proton beam range verification in order to improve targeting accuracy and help to spare vital organs and healthy tissues as much as possible. The study is addressed to eye proton treatments. Here it is of key importance to obtain a good local control on the tumour while sparing the optical nerve and preserving the functionality of the eye. This involves surgically implanting a metal marker in the back of the eye between the tumour and the optic nerve and detecting the proton induced x-ray emissions (PIXE) generated by a therapeutic proton beam in the target. Preliminary experiments and Monte Carlo modelling were performed in an attempt to identify the parameters that will lead to the design of an ideal system. We focused on reducing the experimental background noise and op- timising the detection limit. PIXE signals were successfully acquired with a Cadmium Telluride (CdTe) detector at the Clatterbridge Cancer Centre (UK) and at the CATANA proton beam line (Italy). It was found that PIXE has a linear dependence with the proton fluence but it is energy dependent. This makes it unfeasible to be used for in vivo dosimetry. The most suitable metal was investigated and the minimum detectable residual range for gold and silver was assessed, even at clinical conditions. Statistical models for the multivariate analysis of the acquired data were implemented and a pos- sible use of PIXE was suggested in combination with the current treatment planning tools, to double check the correctness of a treatment delivery.

The detennination of trade routes and social interactions has previously been undertaken using cultural records and archaeological trends. In many regions this infonnation is sparse or inconclusive. By provenancing materials such as the pigments used by Aboriginal artists the movement of materials in the past can be directly investigated. This study is an attempt to characterise and provenance the excavated pigments from Fem Cave, Chillagoe, Southeast Cape York Peninsula. Two techniques, Fourier transform infrared -photoacoustic spectroscopy and proton induced X-ray and gamma-ray emission spectroscopy, have been used to examine the mineralogy and elemental composition of earth pigments. Both these techniques are suited to the examination of solid samples, requiring only very small samples (