Iterative tomography of pipes during operation

The pipe wall thickness was estimated based on three-dimensional images of the pipe recovered from several X-ray projections, which were made in a limited angle of view. Since the effects of scattered radiation and beam hardening are up to 50 % of the main radiation, ignoring them leads to blur of the image and inaccuracy in determining dimensions. To restore pipe images from projections, a volume and/or shell representation of the pipe is used, as well as iterative Bayesian methods. Using these methods, the error in estimating the pipe wall thickness from the projection data can be equal to or less than 300 μm. It has been shown that standard X-ray projections on the film or imaging plates used to obtain data can be used to restore pipe wall thickness profiles in factory conditions.

Radiation Imaging with Caesium Bromide Storage Phosphors

<p>This thesis is centred on the development of a new method to prepare semitransparent CsBr:Eu²⁺ imaging plates for high resolution X-ray radiography. Methods of characterising the performance of these plates, and their application to dual energy imaging and neutron imaging are discussed. The basic preparation method, based on high-pressure uniaxial compression of powder mixtures of CsBr and EuBr₂, produces imaging plates which show good transparency and resolution. These imaging plates have a conversion efficiency of 1.5 pJmR⁻¹mm⁻³ compared to 5.1 pJmR⁻¹mm⁻³ for a commercial needle imaging plate. Water is found to play a critical role in the photostimulated luminescence activation in CsBr:Eu²⁺ storage phosphors, and imaging plates subsequently hydrated at room temperature have an increased conversion efficiency of up to 11 pJmR⁻¹mm⁻³, better than the commercial material. A model has been suggested for the generation of the PSL active site in the imaging plates based on thermomechanical sintering and water-induced crystal regrowth. A precise method for determining the conversion efficiency and stimulation energy of X-ray storage phosphor materials using an integrating sphere has been developed and used to characterise the materials developed in this thesis. A novel read-out method for storage phosphor imaging plates based on flood illumination and a semi-professional digital camera has also been developed and tested. Good quality X-ray images are obtained and the method shows excellent promise as a low-cost, portable X-ray imaging system. A stratified detector using CsBr imaging plates has been developed for use in dual-energy imaging. Results suggest that it is possible to perform dual-energy imaging with this structure. CsBr:Eu²⁺ imaging plates have been produced with added neutron converters for use as thermal neutron imaging plates. An imaging plate with 5 % ¹ºB₂O₃ added as a neutron converter has a PSL output 50 % that of a commercial neutron imaging plate. Neutron imaging with these imaging plates has been successfully demonstrated.</p>

Radiation Imaging with Caesium Bromide Storage Phosphors

<p>This thesis is centred on the development of a new method to prepare semitransparent CsBr:Eu²⁺ imaging plates for high resolution X-ray radiography. Methods of characterising the performance of these plates, and their application to dual energy imaging and neutron imaging are discussed. The basic preparation method, based on high-pressure uniaxial compression of powder mixtures of CsBr and EuBr₂, produces imaging plates which show good transparency and resolution. These imaging plates have a conversion efficiency of 1.5 pJmR⁻¹mm⁻³ compared to 5.1 pJmR⁻¹mm⁻³ for a commercial needle imaging plate. Water is found to play a critical role in the photostimulated luminescence activation in CsBr:Eu²⁺ storage phosphors, and imaging plates subsequently hydrated at room temperature have an increased conversion efficiency of up to 11 pJmR⁻¹mm⁻³, better than the commercial material. A model has been suggested for the generation of the PSL active site in the imaging plates based on thermomechanical sintering and water-induced crystal regrowth. A precise method for determining the conversion efficiency and stimulation energy of X-ray storage phosphor materials using an integrating sphere has been developed and used to characterise the materials developed in this thesis. A novel read-out method for storage phosphor imaging plates based on flood illumination and a semi-professional digital camera has also been developed and tested. Good quality X-ray images are obtained and the method shows excellent promise as a low-cost, portable X-ray imaging system. A stratified detector using CsBr imaging plates has been developed for use in dual-energy imaging. Results suggest that it is possible to perform dual-energy imaging with this structure. CsBr:Eu²⁺ imaging plates have been produced with added neutron converters for use as thermal neutron imaging plates. An imaging plate with 5 % ¹ºB₂O₃ added as a neutron converter has a PSL output 50 % that of a commercial neutron imaging plate. Neutron imaging with these imaging plates has been successfully demonstrated.</p>

Light Scattering in Glass Ceramic X-ray Imaging Plates

<p>Glass ceramic materials have been suggested as a possible high resolution replacement for current commercial storage phosphor imaging plates. The low spatial frequency of the current plates is caused by strong scattering of the laser light incident on the plate during the read-out process. Glass ceramic materials show very small scattering due to their transparent nature, which should lead to a higher resolution. However, a competing argument is the small amount of scattering that does occur travels a much greater distance in the plate, limiting the resolution. The aim of this thesis was to simulate the scattering of light in imaging plates and use this to optimise the trade-off between resolution, sensitivity and transparency which is implicit in plate design. Additionally, experiments were performed to determine the resolution of glass ceramic and commercial imaging plates. Simulations show that high resolution can be achieved in both the strong and weak scattering limits, corresponding to opaque and transparent materials. Increasing the absorption of the laser light increases the resolution, as does decreasing the laser beam diameter and power. An increase in the resolution almost always comes at a cost of a decrease in the sensitivity. The resolutions of an Agfa MD30 and glass ceramic imaging plate were found to be 4:5 line pairs/mm and 6:5 - 8:0 line pairs/mm respectively for an MTF equal to 0:2.</p>

Light Scattering in Glass Ceramic X-ray Imaging Plates

<p>Glass ceramic materials have been suggested as a possible high resolution replacement for current commercial storage phosphor imaging plates. The low spatial frequency of the current plates is caused by strong scattering of the laser light incident on the plate during the read-out process. Glass ceramic materials show very small scattering due to their transparent nature, which should lead to a higher resolution. However, a competing argument is the small amount of scattering that does occur travels a much greater distance in the plate, limiting the resolution. The aim of this thesis was to simulate the scattering of light in imaging plates and use this to optimise the trade-off between resolution, sensitivity and transparency which is implicit in plate design. Additionally, experiments were performed to determine the resolution of glass ceramic and commercial imaging plates. Simulations show that high resolution can be achieved in both the strong and weak scattering limits, corresponding to opaque and transparent materials. Increasing the absorption of the laser light increases the resolution, as does decreasing the laser beam diameter and power. An increase in the resolution almost always comes at a cost of a decrease in the sensitivity. The resolutions of an Agfa MD30 and glass ceramic imaging plate were found to be 4:5 line pairs/mm and 6:5 - 8:0 line pairs/mm respectively for an MTF equal to 0:2.</p>

A Photo and Thermally Stimulated Luminescence Study of BaCl2:Eu2+ with Application to Neutron Imaging

<p>This thesis presents the results of a photo and thermally stimulated luminescence study of europium-doped barium chloride in relation to its potential application as a storage phosphor in glass ceramics for radiation imaging, particularly for neutron imaging. Previous work done on lithium borate (LiBO) glasses containing BaCl2:Eu2+ nanocrystals at Victoria University of Wellington had demonstrated comparable imaging capability with commercially available BaFBr:Eu2+ based imaging plates, though the sensitivity and spatial resolution were inferior to that material, and there was a substantial afterglow during the read-out process which degraded any image. These problems are addressed here. The effect of various different co-dopants on the storage properties was examined using the thermally stimulated luminescence (TSL) technique, with dopants primarily chosen from the alkali and alkaline earth elements. The resulting glow curves have been analysed to determine the activation energies associated with the various traps, and tentative assignments of structural defects to the various glow curve peaks are proposed. It was found that Li+ and Na+ gave small increases (20% and 50% respectively) in efficiency, though other dopants tended to reduce the overall output. In particular, K+ and Rb+ were found to substantially reduce the output efficiency. It was found that Li+ co-doped BaCl2:Eu2+ contained thermally unstable traps which at room temperature could result in the observed afterglow in LiBO/BaCl2 glass ceramics through a read-out induced phototransfer process. The experimental measurements required substantial hardware and software development of the existing VUW facilities for TSL, and these improvements are also described here. The most significant improvements are an extension of the operating range at the lower end of the existing TSL spectrometer to -50 degrees C through a cooled gas flow system, and the engineering of a completely new system to record TSL from 25 K to 400 K.</p>

A Photo and Thermally Stimulated Luminescence Study of BaCl2:Eu2+ with Application to Neutron Imaging

<p>This thesis presents the results of a photo and thermally stimulated luminescence study of europium-doped barium chloride in relation to its potential application as a storage phosphor in glass ceramics for radiation imaging, particularly for neutron imaging. Previous work done on lithium borate (LiBO) glasses containing BaCl2:Eu2+ nanocrystals at Victoria University of Wellington had demonstrated comparable imaging capability with commercially available BaFBr:Eu2+ based imaging plates, though the sensitivity and spatial resolution were inferior to that material, and there was a substantial afterglow during the read-out process which degraded any image. These problems are addressed here. The effect of various different co-dopants on the storage properties was examined using the thermally stimulated luminescence (TSL) technique, with dopants primarily chosen from the alkali and alkaline earth elements. The resulting glow curves have been analysed to determine the activation energies associated with the various traps, and tentative assignments of structural defects to the various glow curve peaks are proposed. It was found that Li+ and Na+ gave small increases (20% and 50% respectively) in efficiency, though other dopants tended to reduce the overall output. In particular, K+ and Rb+ were found to substantially reduce the output efficiency. It was found that Li+ co-doped BaCl2:Eu2+ contained thermally unstable traps which at room temperature could result in the observed afterglow in LiBO/BaCl2 glass ceramics through a read-out induced phototransfer process. The experimental measurements required substantial hardware and software development of the existing VUW facilities for TSL, and these improvements are also described here. The most significant improvements are an extension of the operating range at the lower end of the existing TSL spectrometer to -50 degrees C through a cooled gas flow system, and the engineering of a completely new system to record TSL from 25 K to 400 K.</p>

Experimental analysis of mechanical behaviour and residual stresses of EN-36C alloy steel with and without tempering

The intense demands of nickel chromium case hardened steel (EN-36C) alloy steel in different engineering applications are increasing day by day due to its cheap and easy availability. The effect of different stages of tempering on EN-36C alloy steel has been carried out to check the mechanical behavioural, microstructural properties and residual stresses in the present work. The effect of tempering on response variables viz., material removal rate, surface roughness, tool tip temperature and residual stresses are evaluated. The cosα method is used to measure the residual stresses in the specimen using two-dimensional detectors such as imaging plates. Further, the influence of tempering on mechanical properties such as tensile strength, hardness, toughness and percentage elongation has been observed. Experimental results depicted that the ductility and toughness are improved without significant change in hardness in the specimen tempered at 500°C. The mechanical properties of specimens tempered at 500°C are found to be a tensile strength of 680.42 MPa, hardness 92 Rockwell hardness of scale B and toughness 187 J. The maximum value of material removal rate (12596.80 mm3/min), minimum tool tip temperature (61.33°C), average surface roughness ( Ra = 1.93, Rq = 2.36, Rz = 10.30) and lowest residual stress 217 MPa are observed in the specimens tempered at 500°C.

Compact spectroscopy of keV to MeV X-rays from a laser wakefield accelerator

We reconstruct spectra of secondary X-rays from a tunable 250–350 MeV laser wakefield electron accelerator from single-shot X-ray depth-energy measurements in a compact (7.5 × 7.5 × 15 cm), modular X-ray calorimeter made of alternating layers of absorbing materials and imaging plates. X-rays range from few-keV betatron to few-MeV inverse Compton to > 100 MeV bremsstrahlung emission, and are characterized both individually and in mixtures. Geant4 simulations of energy deposition of single-energy X-rays in the stack generate an energy-vs-depth response matrix for a given stack configuration. An iterative reconstruction algorithm based on analytic models of betatron, inverse Compton and bremsstrahlung photon energy distributions then unfolds X-ray spectra, typically within a minute. We discuss uncertainties, limitations and extensions of both measurement and reconstruction methods.

Analisa Artefak Pada Hasil Radiograf Yang Timbul Akibat Pengolahan Computed Radiography

Artefacts are structures or appearances that are not normally present on radiographs, errors in radiographic processing may be due to technical errors or film processing errors. This research was conducted using Descriptive methods, with the type of literature study that aims to examine the causes of artifacts that can occur as a result of improper handling of film processing errors.The results of the analysis concluded that the frequent occurrence of artifacts in the processing of Computed Radiography is caused by two factors, that is the use of imaging plates and grids lisolm. His advice should be in the processing using Computed Radigraphy the officer must be more careful and pay attention to the components in Computed Radiography.