Magnetic resonance imaging of microbubbles in a superheated emulsion chamber for brachytherapy dosimetry

This paper describes development of magnetic resonance imaging (MRI) techniques for three-dimensional (3D) imaging of a position-sensitive detector for brachytherapy dosimetry. The detector is a 0.5 l chamber containing an emulsion of halocarbon-115 droplets in a tissue-equivalent glycerin-based gel. The halocarbon droplets are highly superheated and expand into vapor microbubbles upon irradiation. Brachytherapy sources can be inserted into the superheated emulsion chamber to create distributions of bubbles. Three-dimensional MRI of the chamber is then performed. A 3D gradient-echo technique was optimized for spatial resolution and contrast between bubbles and gel. Susceptibility gradients at the interfaces between bubbles and gel are exploited to enhance contrast so microscopic bubbles can be imaged using relatively large voxel sizes. Three-dimensional gradient-echo images are obtained with an isotropic resolution of 300 microns over a 77 mm x 77 mm x 9.6 mm field-of-view in an imaging time of 14 min. A post-processing technique was developed to semi-automatically segment the bubbles from the images and to assess dose distributions based on the measured bubble densities. Relative dose distributions are computed from MR images for a 125I brachytherapy source and the results compare favorably to relative radial dose distributions calculated as recommended by Task Group 43 of the American Association of Physicists in Medicine.     

Calculation procedure of potential alpha energy concentration with continuous air sampling

A continuous potential alpha energy concentration monitor was developed to estimate the lung dose for inhalation of radon progeny. A silicon semiconductor detector was used as a detector. The build-up method was used and alpha particles emitted from 218Po, 214Po, 212Bi, and 212Po were detected. As 218Po and 212Bi have alpha particles of nearly the same energy, three detecting channels were set up. Counts corresponding to each nuclide were sent to a printer every 30 min. For the purpose of determining the potential alpha energy concentration of radon progeny continuously, a proper calculation procedure was investigated in detail. With this method, 218Po concentration and potential alpha energy concentration of radon progeny could be continuously obtained. The potential alpha energy concentration based on this procedure agreed well with that calculated from individual radon progeny concentration. When the measurement was done at 30-min intervals, the minimum detectable concentrations of 218Po concentration and equilibrium equivalent radon concentration were 0.3 Bq m(-3) and 0.15 Bq m(-3), respectively. The monitor can be used not only to estimate the lung dose but also to analyze environmental behavior of radon progeny.     

Modelling DNA damage induced by different energy photons and tritium beta-particles

PURPOSE: To model the production of single- and double-strand breaks (ssb and dsb) in DNA by ionizing radiations. To compare the predicted effectiveness of different energy photon radiations and tritium beta-particles. MATERIALS AND METHODS: Modelling is carried out by Monte Carlo and includes consideration of direct energy depositions in DNA molecules, the production of species, their diffusion and interactions with each other and DNA. Computer-generated electron tracks in liquid water are used to model energy deposition and to derive the initial positions of chemical species. Atomistic representation of the DNA in B form with a first hydration shell is used. Photon radiations in the energy range 70keV-1MeV and tritium beta-particles are considered. RESULTS: A tentative increase for dsb yield has been predicted for 70 keV photons and tritium compared with 137Cs. This increase is more pronounced for complex dsb. Double-strand breaks are much more prone compared with ssb to combine with additional strand breaks and base damage, which contributes to break complexity. At least half of DNA breaks are hydroxyl radical mediated. CONCLUSIONS: The developed model makes predictions compatible with features of available experimental data. Break complexity has to be addressed in biophysical modelling when the relative effectiveness of radiations in DNA damage is studied. Obtained data strongly argue against the dominance of direct radiation action in DNA damage in the cellular environment predicted by some theoretical studies.     

薄样技术-能量色散X射线荧光光谱法测定钯铂金

采用树脂分离富集金矿和铜阳极泥中的Pd、Pt、Au,结合薄样技术,利用自制X射线荧光(XRF)能谱仪同时测定这3种元素。对3种型号树脂进行了选择,确定了Amberlyst A26树脂为分离树脂,并采用单因素法对Amberlyst A26树脂柱高、流速和盐酸浓度进行了优化,确定了最佳实验条件分别为柱高10 cm、流速3 mL/min和盐酸浓度0.2 mol/L。同时对XRF分析方法进行了方法学验证。XRF能谱仪采用Mo靶激发,新型SDD探测器,结合优化的薄样技术,基本消除基体效应,可用内标法定量;仪器检出限(LLD)Pd、Pt、Au分别为0.021、0.019、0.015 μg/mL,方法检出限(LDM)分别为 0.066、0.062、0.050 μg/mL;采用11种元素的混合标准测得RSD在1.6%~7.5%之间。所测金矿样品的结果与国标法结果一致,铜阳极泥的测定结果与ICP-MS法结果基本一致。     

A position-sensitive superheated emulsion chamber for three-dimensional photon dosimetry

A position-sensitive detector chamber is introduced for the three-dimensional (3D) dosimetry of photon-emitting brachytherapy sources. The detector is based on an extremely fine suspension of monochloropentafluoroethane droplets emulsified in a gel. The droplets are highly superheated at room temperature and their evaporation can be triggered by photon interactions, leading to the formation of microscopic bubbles. Thus, when photon-emitting brachytherapy sources are inserted into the detector, bubble distributions form around them, enabling visualization of the radiation field. The tissue-equivalent emulsifier gel is highly viscous and keeps the bubbles immobilized at the location of their formation. Bubbles can then be imaged by nuclear magnetic resonance or optical scanning techniques. After the imaging, the detector can be pressurized in order to recondense the bubbles to the liquid phase. In a few minutes, the device is annealed and ready to be used again for repeated measurements improving the counting statistics. The photon sensitivity of the monochloropentafluoroethane droplets was determined with highly filtered, quasi-monochromatic x-ray beams and radionuclide gamma sources. The air-kerma response presents a broad maximum at low energies, due to the relatively high effective atomic number of the halocarbon molecule. A prototype chamber was built and successfully tested: bubble distributions deriving from the insertion of a 125I source were imaged by means of a slice-selective 3D gradient-echo technique. These experiments confirm the potential and viability of this new approach to 3D photon dosimetry.     

Influence of Rare Earth on Carbide in Weld Metal

Inhardsteelwelds ,thehighcarboncontentisnecessaryandlotsofcarbidesareexpectedtoforminordertoincreasethehardnessandwearresistanceofmaterial.Buttheweldshave poorstrengthandtoughnessowingtotheformationofhighcarbonmartensiteandnetworkcarbides .Ifthecarbidesareturnedinto granularformanddistributedevenly ,thetoughnessofweldmetalcouldbemarkedlyin creased .Forthispurpose ,thehighcarbonNb Ti V Zr REalloysystemwasdesigned .Niobium ,titani um ,vanadiumandzirconiumcouldcombinewithcarbontoformlotsofcarb…     

In-phantom dosimetry and spectrometry of photoneutrons from an 18 MV linear accelerator

A combination of three superheated drop detectors with different neutron energy responses was developed to evaluate dose-equivalent and energy distributions of photoneutrons in a phantom irradiated by radiotherapy high-energy x-ray beams. One of the three detectors measures the total neutron dose equivalent and the other two measure the contributions from fast neutrons above 1 and 5.5 MeV, respectively. In order to test the new method, the neutron field produced by the 10 cm X 10 cm x-ray beam of an 18 MV radiotherapy accelerator was studied. Measurements were performed inside a tissue-equivalent liquid phantom, at depths of 1, 5, 10 and 15 cm and at lateral distances of 0, 10, and 20 cm from the central axis. These data were used to calculate the average integral dose to the radiotherapy patient from direct neutrons as well as from neutrons transmitted through the accelerator head. The characteristics of the dosimeters were confirmed by results in excellent agreement with those of prior studies. Track etch detectors were also used and provided an independent verification of the validity of this new technique. Within the primary beam, we measured a neutron entrance dose equivalent of 4.5 mSv per Gy of photons. It was observed that fast neutrons above 1 MeV deliver most of the total neutron dose along the beam axis. Their relative contribution increases with depth, from about 60% at the entrance to over 90% at a depth of 10 cm. Thus, the average energy increases with depth in the phantom as neutron spectra harden.     

Solidification of Pb particles embedded in Al

Hypermonotectic alloys of Al-5 wt% Pb and Al-5 wt% Pb-0.5 wt% X where X = Mn, Cu, Zn, Fe and Si have been manufactured by chill-casting and melt-spinning. The resulting microstructures have been examined by a combination of optical microscopy, scanning and transmission electron microscopy, and electron probe microanalysis. The as-solidified hypermonotectic alloys exhibit a homogeneous bimodal distribution of faceted Pb particles embedded in a matrix of Al, with chill-cast Pb particle sizes of 1–2 μm and 5–50 μm, and melt-spun Pb particle sizes of 5–10 nm and 50–100 nm. The larger Pb particles are formed during cooling through the region of liquid immiscibility while the smaller Pb particles are formed during monotectic solidification of the Al matrix. The Pb particles exhibit a cube-cube orientation relationship with the Al matrix, and a truncated octahedral shape with {111} and {100} facets. The as-solidified Pb particle distributions are resistant to coarsening during post-solidification heat treatment. The equilibrium Pb particle shape and therefore the anisotropy of solid Al-solid Pb and solid Al-liquid Pb surface energies have been monitored by in situ heating in the transmission electron microscope over the temperature range between room temperature and 550°C. The anisotropy of solid Al-solid Pb surface energy is constant between room temperature and the Pb melting point, with the {100} surface energy 14% greater than the {111} surface energy, in good agreement with geometric near-neighbour bond energy calculations. The {100} facets disappear when the Pb particles melt, and the anisotropy of solid Al-liquid Pb surface energy decreases gradually with increasing temperature above the Pb melting point, until the Pb particles become spherical at about 550°C. The kinetics of Pb particle solidification have been examined by heating and cooling experiments in a differential scanning calorimeter. Pb particle solidification is nucleated catalytically by the Al matrix on the {111} facet surfaces, with an undercooling of 22K and a contact angle of 21°C. Ternary additions of Mn, Cu, Zn and Fe do not influence the Pb particle solidification behaviour, but Si is a potent catalyst and stimulates the Pb particles to solidify close to the equilibrium Pb melting point.     

高锰钢铸渗SiC颗粒过程中粒子分解特性研究

分析了铁基体复合SiC陶瓷颗粒的前景,提出改善SiC在铁基中分解的新方法,并在实验室条件下,采用V-EPC法(真空负压实型铸造法)制备了SiCp/高锰钢基复合材料.通过金相分析、扫描电镜(SEM)、能谱仪(EDS)及X射线衍射(XRD)等测试手段,研究了SiC颗粒铸渗高锰钢过程中SiC粒子的分解特征及粒子周围合金元素分...     

Numerical calculation of energy deposition by high-energy electron beams: III-B. Improvements to the 6D phase space evolution model

The phase space evolution model of Huizenga and Storchi, Morawska-Kaczyńska and Huizenga and Janssen et al has been modified to (i) allow application on currently available computer equipment with limited memory (128 Megabytes) and (ii) allow 3D dose calculations based on 3D computer tomographic patient data. This is a further development aimed at the use of the phase space evolution model in radiotherapy electrons beam treatment planning. The first modification regards the application of depth evolution of the phase space state combined with an alternative method to transport back-scattered electrons. This depth evolution method requires of the order of 15 times less computer memory than the energy evolution method. Results of previous and new electron transport methods are compared and show that the new electron transport method for back-scattered electrons hardly affects the accuracy of the calculated dose distributions. The second modification regards the simulation of electron transport through tissues with varying densities by applying distributed electron transport through similarly composed media with a limited number of fixed densities. Results of non-distributed and distributed electron transport are compared and show that the distributed electron transport method hardly affects the accuracy of the calculated dose distributions. It is also shown that the results of the new dose distribution calculations are still in good agreement with and require significantly less computation time than results obtained with the EGS4 Monte Carlo method.     

Modeling of deposition of coke particles in the top part of soderberg anode

The rate of free deposition of coke particles with diameters from 2 to 8 mm in a liquid modeling of a coal tar pitch was measured. It was shown that the value of that factor is proportional to the particle size and inversely proportional to the medium viscosity. Empirical equations for estimating the rate of free and hindered depositions of coke particles were suggested.     

On the 60th birthday of Victor Vladimirovich Polyakov

The rate of free deposition of coke particles with diameters from 2 to 8 mm in a liquid modeling of a coal tar pitch was measured. It was shown that the value of that factor is proportional to the particle size and inversely proportional to the medium viscosity. Empirical equations for estimating the rate of free and hindered depositions of coke particles were suggested.     

Neutron measurements in the stray field produced by 158 GeV c(-1) per nucleon lead ion beams

This paper discusses measurements carried out at CERN in the stray radiation field produced by 158 GeV c(-1) per nucleon 208Pb82+ ions. The purpose was to test and intercompare the response of several detectors, mainly neutron measuring devices, and to determine the neutron spectral fluence as well as the microdosimetric (absorbed dose and dose equivalent) distributions in different locations around the shielding. Both active instruments and passive dosimeters were employed, including different types of Andersson-Braun rem counters, a tissue equivalent proportional counter, a set of superheated drop detectors, a Bonner sphere system, and different types of ion chambers. Activation measurements with 12C plastic scintillators and with 32S pellets were also performed to assess the neutron yield of high energy lead ions interacting with a thin gold target. The results are compared with previous measurements and with measurements made during proton runs.     

New methods for the investigation of blood-biomaterial interaction

Quantitative microscopy with integrated image processing is a useful tool for investigation of the interaction of blood components with biomaterials. We have developed new automated measuring devices suitable for simultaneously characterizing biological cells (size, shape, localization, migration, electrophoresis), synthetic particles (electrophoretic fingerprinting), and dialysis membranes (morphology, electric charge). These techniques are useful for the investigation of cell adherence on biomaterials, localization of cells in membrane filters (Chemotaxis), characterization of the protein adsorption on model systems, detection of cytokines (produced after lymphocyte-biomaterial contact), and estimation of morphological properties and charge distribution in dialysis membranes.     

Measurements of the grain boundary energy and anisotropy in tin

The three-dimensional (3-D) geometry of the triple junction formed between two solid Sn-rich particles and a Pb-rich liquid matrix is used to measure the interfacial energy and its anisotropy for individual grain boundaries. The anisotropy is determined using a Cahn-Hoffman capillarity vector analysis of the energy balance at a triple junction. The absolute solid-solid grain bondary energy for each individual boundary is then determined by using the known value for the solid-liquid energy. A total of 136 boundaries are analyzed, with 46 of them forming grain boundaries. The remaining boundaries are found to be wetted boundaries with thin-liquid films formed between the two particles. A correlation between the low interfacial energy and the probability of occurrence for that disorientation is also observed. We also show that the anisotropy, as quantified by the magnitude of the torque term, is a significant portion of the total interfacial energy, especially for low energy boundaries. The degree of twist vs tilt of the boundaries is also analyzed. As expected, there are more tilt boundaries within the system than twist boundaries and most of the low energy boundaries have a mixed tilt-twist character.     

Texture distributions imaged by energy dispersive X-ray diffraction

An X-ray scanning apparatus has been developed for the study of texture topography and element distributions on bulk sample surfaces. The set-up consists of a white X-ray source, a collimator system to produce a narrow primary beam, an x-y sample stage with stepper motors, and an EDX detecting system. The apparatus is controlled by a microcomputer. The spectrum of secondary X-rays is composed of broad diffraction peaks, sharp characteristic fluorescence lines, and a low background of scattered radiation. Peak separation and intensity measurement is performed by energy dispersive X-ray spectroscopy (EDX). The density distributions of selected crystallographic directions or elements in the sample surface are acquired spot by spot, and represented by false-colour images. Several texture distributions as well as element composition images can be obtained simultaneously. Local resolution is presently limited to 0.2 mm, due to the low intensity of a collimated primary X-ray beam.     

喷雾干燥塔在氧化铝回转窑烧结中的应用与数值仿真研究

建立了氧化铝回转窑喷雾干燥塔的3D数值模型,应用CFD商业软件Fluent对其进行仿真计算。分析了塔内部温度、速度的分布及颗粒运动轨道与干燥速率。结果表明,干燥塔温度和速度分布较为合理,干燥带集中发生在中上部;塔内液滴的干燥速度较快,干燥塔的设计能够满足工艺的要求。实际工业应用表明,该工艺不但能降低建筑成本,也能够节约回转窑能耗。     

氧化铝回转窑喷雾干燥塔的数值仿真

建立了氧化铝回转窑喷雾干燥塔的3D数值模型,应用CFD商业软件Fluent对其进行仿真计算。分析了塔内部温度、速度的分布及颗粒运动轨道与干燥速率。结果表明,干燥塔温度和速度分布较为合理,干燥带集中发生在中上部;塔内液滴的干燥速度较快,干燥塔的设计能够满足工艺的要求。实际工业应用表明,该工艺不但能降低建筑成本,也能够节约回转窑能耗。     

Discussion of “On the free energy of formation of TiC and Al4C3”

Several years ago, Banerji and Reif^[1] reported some very interesting studies on a process to react Ti and C in molten Al to form particles of TiC. The process was used to prepare a master alloy with a fine dispersion of TiC to inoculate Al for grain refinement. Approximately 2 wt pct of preheated graphite particles were stirred into the Al-5 to 10 pct Ti melts. The authors explained that the melts needed to be superheated above 1000 °C to avoid the undesirable formation of A1₄C₃ and Ti₃AlC at the TiC/melt interface. Their explanation for this phenomenon was based on thermodynamics. They observed that the standard free energy of formation curves for AI4C3 and TiC cross near 1175 °C, with A1₄C₃ having the lower free energy of formation below this temperature. There are several aspects of this work which merit further discussion.