Imaging near-field compton backscattered X-rays using Pinhole and coded masks

Research was conducted to understand the behaviour of an X-ray backscatter imaging system using coded masks to view complex scenes. These spatially multiplexing images were compared to those collected using a single pinhole and a commercial flying spot (time multiplexing) imaging system. An X-ray backscatter system was constructed to perform experiments with pinholes and coded masks. A novel fabrication technique adopting 3D printing was developed to rapidly create low-cost alternatives to the traditional drilled tungsten coded masks. Subsequently, this allowed for the retention of ideal square open elements within the mask, along with the benefit of having a self-supporting structure. Conventional methods of manufacturing coded masks compromise the encoding process by using round holes in place of the square elements to achieve a self-supporting structure. Previous work has suggested that coded masks with a low open fraction (i.e. < 0.5) will yield a higher signal-to-noise ratio than those with a 0.5 open fraction. As part of this study, the following low open fraction coded mask was calculated; dilute uniformly redundant array (DURA), Singer and the biquadratic residue (BR). In total 111 new array patterns were calculated. Xray backscatter images are presented from examples of these coded masks with images reconstructed via cross-correlation and blind deconvolution. Overall, for coded mask imaging, the best results were from the 19 MURA for its signalto-noise with a typical 2-12 second (s) exposure time. Consequently, there was little evidence to support the benefit of lower open fractions. Pinhole and coded mask images were somewhat comparable with the pinhole requiring a longer exposure time of 60-300 s. While not ideal due to barrel distortion, the images from the flying spot system exhibited higher signal-to-noise ratios and resolutions but required an exposure time of 70 seconds, longer than those for the MUR

Preparation and Certification of IRMM-075

A set of 6 new synthetic mixtures with n(236U)/n(238U) isotope ratios varying from 10-4 to 10-9 has been prepared and certified. Natural uranium with low 236U isotope abundance and enriched 236U were both purified using well proven chemical methodology extensively tested in the preparation of other uranium synthetic mixtures such as IRMM-074. The purification involved separation on anion and cation columns followed by precipitation as peroxide. Manipulations were carried out in separate new glove-boxes to avoid cross contamination. The oxides were sintered into U3O8 in an oven installed in a glove-box with controlled humidity. Primary solutions of the same concentration were prepared by dissolving the oxides of 236U and natU. From the 236U solution four dilutions were made by weighing. Weighed amounts of the dilutions of 236U and weighed amounts of natU were mixed to form a set of 236U/238U mixtures at a concentration of 1 mg U*g-1. The final solutions were dispensed into quartz ampoules which were subsequently flame sealed. Verification of the mixtures IRMM-075/1-7 was performed by TRITON TIMS measurements using Faraday collectors and secondary electron multiplier in combination with an RPQ energy filter for improved abundance sensitivity. The results agreed well with the certified values obtained from the mixing calculations. The uncertainties contributing to the final uncertainties of the isotopic ratios are the weighing errors, the measured impurities in each starting material, the stoichiometry of the oxides and the isotopic abundances of each. The method for the preparation and mixing are described and the certification and verification procedures are reported.JRC.D.4-Isotope measurement

Rapid prototyping-coded masks for x-ray backscatter imaging

Coded masks (CM) often lack a self-supporting structure that is difficult to manufacture without recourse to drilled holes in place of ideal square apertures, degrading imaging properties. An alternative approach is presented with three-dimensional (3-D) printed CM molds cast with a radio-opaque material that allows square elements to be retained. Two methods are presented; hot casting a bismuth alloy (density 8.6  g cm  −  3) and cold casting with tungsten powder/epoxy resin (densities 9.6 and 10.6  g cm  −  3). A critical review of 3-D printed-CM fabrication along with some typical x-ray backscatter images is presented. A signal-to-noise ratio from both the machined tungsten and cold cast 3-D printed mask were comparable, with the former having a slight advantage. Also, 3-D printed cold cast masks were found to be more economical and easier to rapid prototype over traditional drilled tungsten masks

Update on REIMEP-15: Isotopic Ratios of uranium in UF6

The REIMEP (Regular European Interlaboratory Measurement Evaluation Programme) campaign 15 for isotopic ratios of uranium in UF6 samples has been completed in 2002. The participants received 4 samples of low-enriched or slightly depleted uranium in the form of UF6 in standard monel capsules. The samples were prepared at IRMM by mixing uranium reference materials certified by gas mass-spectrometry in the form of UF6. The minor isotopes, 234U and 236U were certified at IRMM by Thermal Isotope Mass-spectrometry (TIMS) using a MAT262-RPQ mass spectrometer in ion counting mode. Certified values were sent to the participating laboratories immediately after receiving their measured results. The measured results and their comparison with the certified values allowed an overall view of the analytical capability in the nuclear field to measure uranium isotopic ratios in UF6 samples. However, for the so-called minor ratio 234U.238U the comparison of IRMM¿s certified values with all the participants results showed a significant relative deviation of about 2%, which is by far larger than the typical uncertainties expected for this kind of measurements. This significant deviation was considered disappointing for IRMM as the leading European nuclear safeguards metrology institute. This problem has now overcome first by measurements using the new TRITON TIMS at IRMM and second by a thorough investigation on the reasons for the deviation observed in the past.JRC.D.4-Isotope measurement

Preparation and Certification of IRMM-3636, IRMM-3636a and IRMM-3636b

Isotope reference materials IRMM-3636 was prepared by gravimetrically mixing of solutions from highly enriched 99.96% 233U (IRMM-3630) and highly enriched 99.97% 236U (IRMM-3660) in order to obtain an isotopic ratio n(233U)/n(236U) close to unity. IRMM-3636a and IRMM-3636b were prepared from IRMM-3636 by gravimetrical dilution. The primary solution, IRMM-3636 is for the time being not yet available for external users. The certified isotope content values for IRMM-3636a of 4.27988(54)*10-7 mol U per g of solution and for IRMM-3636b of 2.21802(61)*10-8 mol U per g of solution and the certified isotope amount ratios have been established by mass metrology, subsequently the primary solution IRMM-3636 was verified by isotope mass spectrometry. The methodology used in the preparation and certification was similar to that of comparable uranium mixtures made in the past. The uncertainties contributing to the final uncertainties of the isotopic ratios are the weighing errors, the measured impurities in each starting material, the stoichiometry of the oxides and the isotopic abundances of each of the starting materials. The method for the preparation and mixing is described and the certification and verification procedures are reported. Verification of IRMM-3636 was performed by TRITON TIMS measurements using Faraday collectors and secondary electron multiplier in combination with an RPQ energy filter for improved abundance sensitivity. The results agreed well with the certified values obtained from the mixing calculations. By mixing the n(233U)/n(236U) double spike with a sample and applying internal mass fractionation correction, the n(235U)/n(238U) ratio of a given sample can be determined with the highest possible accuracy. The Isotopic Reference Materials IRMM-3636, IRMM-3636a and IRMM-3636b are part of a systematic IRMM programme to supply Isotopic Reference Materials of various isotopes at different concentrations. The Isotopic Reference Material is supplied in a sealed quartz ampoule containing 1 mL of a 1 M nitric acid solution.JRC.D.4-Isotope measurement

An artificial X-ray wire test emitter and calculations on the resolution and field of view of X-ray pinhole optics by simulation

The PENELOPE Monte Carlo simulation code was used to evaluate pinhole mask parameters for X-ray backscatter imaging in a security application. This work makes four major contributions: it describes a convenient efficient test object for evaluating X-ray optics, it converts the PENELOPE output into a simulated CCD image, it compactly outlines how image characteristics can be simply and reproducibly quantified, and it gives guidance on suitable materials and geometries for pinhole masks for X-ray imaging that could be applied to more complicated X-ray optics, such as coded masks. A novel test object X-ray emitter with the shape of a thin wire was specifically designed to explore the effect of mask material thickness and pinhole aperture diameter on image quality. Setting the test object to be the X-ray emitter rather than being a passive scatterer increases computational speed. The photon energy distribution of the artificial test object was set flat between selected energy limits to avoid the model being specific to any particular X-ray source technology. The modelled detector is an array of 1040 x 1392 pixels’ area detector inside a lead-lined camera housing. The pixelated detector was modelled by digitising the surface area represented by the PENELOPE phase space file and integrating the energies of the photons impacting each pixel with MATLAB code. The pinhole must be wide enough for sufficient field of view, whilst narrow enough for sufficient spatial resolution and the mask material needs to be thick enough to absorb most X-rays. When the mask material was too thick and the aperture too narrow, a collimation effect occurred. The consequence of excess collimation in a coded aperture is partial coding giving poor image reconstruction. Pure tungsten appears the most versatile material tested, where a 2 mm thickness and 2 mm aperture gives the most appropriate image characteristics for X-ray security imaging

Low open fraction coded masks for x-ray backscatter imaging

Previous research has indicated that coded masks with open fractions <0.5 are optimal for imaging some types of far-field scenes. The open fraction, in this case, refers to the ratio of open elements in the mask, with values <0.5 considered as low open fraction. Research is limited by the sparsity of <0.5 open fractions masks; thus a further 94 lower open fraction arrays are calculated and presented. These include the dilute uniformly redundant array and singer set, along with information on imaging potential, array sizes, and open fractions. Signal-to-noise ratio reveals the 0.5 open fraction modified uniformly redundant array to be the optimal coded mask for near-field x-ray backscatter imaging, over the lower open fraction singer set, dilute uniformly redundant and random arra

The quantitative proteomes of human-induced pluripotent stem cells and embryonic stem cells

An in-depth proteomic comparison of human-induced pluripotent stem cells, and their parent fibroblast cells, with embryonic stem cells shows that the reprogramming process comprehensively remodels protein expression levels, creating cells that closely resemble natural stem cells

Produção de aveia-preta com solução nutritiva e adição de substâncias húmicas

O experimento foi realizado no ano de 1 997, em casa de vegetação, na Faculdade de Agronomia da Universidade Federal do Rio Grande do Sul (UFRGS), utilizando o desenho experimentai de blocos casualizados em parcelas subdivididas com seis repetições. A aveia foi cultivada em areia irrigada, com solução nutritiva completa e quatro doses (0, 10, 20 e 30 mg.L·') de substâncias húmicas, extraídas a partir dos carvões das minas do Capané (Pai ermo CE-4.200 e Palerma CE-4.700), Leão (Leão CE-5.200) e Candiota (Candiota Camada Superior, Candiota Camada Superior, Candiota CE-3.300 e Candiota CE-4.700). Foram avaliadas as seguintes variáveis: matéria seca produzida pela parte aérea e pelas raízes, comprimento das raízes, raio médio das raízes e superfície ocupada pelas raízes. A utilização das tas substâncias aumentou em até 21,88% a produção de matéria seca da parte aérea; em até 1 09,2% o comprimento das raízes e em até 46,69% a superfície ocupada pelas raízes. Os resultados obtidos indicaram que as substâncias húmicas influenciaram o desenvolvimento da parte aérea e das raízes da aveia, e que as substâncias húmicas originadas de diversos carvões atuaram de forma diferente sobre os parâmetros das cinco variáveis analisadas.a split-plot experimental design with treatments arranged in randomized complete blocks, with six repl ications. Black Oats forage was grown in pots with irrigated sartd and four leveis (0, 1 0, 20 and 30 mg.L-1) of humic compounds added to a complete nutrient solution. Humic substances were extracted from Capané (Palerma coais EC-4,200 and EC-4,700), Candiota (Candiota coais superior layer, inferior layer, EC-3,300 and EC- 4,700) and Leão (Leão coai EC-5,200). Aerial part dry matter yield, length of roots, mean radi um o f roots, occupied roots surface and dry matter yield o f rootswere evaluated. Results showed that humic compounds influenced oats roots growing increasing mainly: aerial part dry matter yield in 2 1 ,88%; root length in 1 09,2%; occupied root surface in 46,69%. It is concluded that humic compounds affected black oats roots development. Humic compounds from different raw materiais influenced diversely the five variables that were evaluated

Preparation and Certification of IRMM-1027j, Large-Sized Dried (LSD) Spike

A new set of Large Size Dried (LSD) Spikes for the determination of uranium and plutonium by isotope dilution mass spectrometry in solutions of spent fuel from reprocessing plants has been prepared and certified for uranium and plutonium isotopic contents. The methodology followed was similar to that of previous batches. The solution, made by dissolution of the starting materials in nitric acid, was dispensed directly into individual penicillin vials. This new batch of large size dried spikes contains ca. 50 mg of uranium (235U abundance = 19.7%) and ca. 1.8 mg of plutonium (239Pu abundance = 97.8%) in each individual vial, covered with a light layer of organic material (cellulose acetate butyrate) as stabilizer. The U and Pu amount content was certified based on values from mass metrology. Verification of the amount contents of the spike was done by IDMS at IRMM. The values measured for the batch solution and of the dried covered spikes agreed well with those calculated from the weights of starting materials dissolved and the weights of the final solution.JRC.D.4-Isotope measurement