Sterilization of health care products by 5 MeV bremsstrahlung (X ray)

Radiation sensitivities of . pumilus and spores were examined to bremsstrahlung of 5 MeV EB and Cobalt -60 γ rays in order to confirm the effects of radiation and dose rate. Biological indicators (SPORTROL, NAmSA, USA) were irradiated with the X ray in the dose rate range of 4.7–47kGy/h. D-value of spores was 1.4–1.5 kGy, and that of was 1.1–1.3 kGy. The D-values of and have very small dose rate dependences to X ray, and the D-values are similar to those of γ ray. Dose distribution by X-ray and γ irradiation was measured for cartons containing 32 unit dialyzers. The D_max./D_min. of the X-ray irradiation (1.2) was smaller than that of γ ray (1.3).     

Monte Carlo studies of a novel X-ray tube anode design

When energetic electrons are incident on high atomic number absorbers, a substantial fraction is back-scattered. This phenomenon is responsible for several undesirable effects in X-ray tubes, in particular a reduction in the X-ray output. The extent of this shortfall has been estimated by using Monte Carlo simulation to start electrons at increasing depth inside the anode, the results indicating that an output enhancement of nearly 50% could be achieved in principle if the electrons wasted in back-scatter events could be trapped inside a tungsten anode. To test this idea a further set of simulations were done for a novel anode geometry. Results showed that X-ray tube efficiencies might be substantially enhanced by this approach.     

A high-performance X-ray system for medical device irradiation

A new concept of X-ray irradiator for low-density products on pallets is proposed. Monte Carlo simulations are applied to predict the performance of this system. The Monte Carlo predictions reveal in good agreement with experimental data obtained using products of different densities.     

A high energy X-ray diffraction study of sol–gel derived (Ta2O5) x (SiO2)1? x glasses ( x =?0.05, 0.11 and 0.25)—elucidating the role of tantalum in silica

High energy X-ray diffraction (HEXRD) has been used to study the atomic structure of (Ta₂O₅) _x (SiO₂)_1−x (x = 0.05, 0.11 and 0.25) xerogels; the direct interpretation of the resultant data has been augmented using reverse Monte Carlo (RMC) modelling. For the first time in this type of material, two Ta–O correlations have been identified (at ∼1.8 ? and 2.0 ?). The RMC modelling approach explicitly used MAS-NMR data to define its constraints; when combined with HEXRD data, it helps to confirm the more directly determined total coordination of five for the two Ta–O correlation distances and suggests Ta···Si and Ta···Ta coordination distances of ∼3.3 ? and ∼3.8 ?, respectively. The O···O and Si···Si distances and coordination numbers associated with the host silica network suggest that the Ta (V) is acting as a network modifier. The way in which the Ta–O correlations are affected by composition and calcination temperature suggest some phase separation in the (Ta₂O₅)_0.25(SiO₂)_0.75 sample. However, in general, the results indicate good mixing of the component oxides.      

X-ray imaging using the radiation diffracted by polycrystalline materials

Imaging requires not only an area detector but also optics to relate the elements of the object to those of the detector. For X-rays optical elements based on reflection or refraction allowing the imaging of objects of several mm size are not available. Therefore, image formation like in the human eye cannot be achieved, but an approach realized in the eyes of insects where each facet has its own optics, has to be used. In the X-ray regime such a system can be realized by an arrangement of collimating tubes guiding the radiation from a region of the sample to the corresponding area of the detector and suppressing cross-fire from other regions.

Such an imaging system consisting of a microchannel plate in front of a CCD-detector has been installed on the 2Θ-arm of a 4-circle diffractometer at beamline G3 at HASYLAB, DESY. With this instrument, images as a function of one or more parameters can be collected. The structure of the data obtained in this way is distinct from those obtained by conventional diffraction techniques mostly yielding only one intensity value per scanning step and therefore requires different strategies for processing.     

Predicting MWD and Branching Distribution of Terminally Branched Polymers Undergoing Random Scission

A new semi‐analytical approach to model simultaneous chain scission and branching is described that assumes the separation of the scission and the branching problem. The required properties of the linear segments or primary polymers forming the branched architectures are found by a kinetic model. The general rules for the construction of branched architectures from populations of linear segments then lead to an analytical expression for the branching distribution and a semi‐analytical expression for the bivariate length/branching distribution. The method is applied to the scission of an initially branched polymer and subsequent terminal branching on scission points and activated terminal double bonds. Exact agreement is found with Monte Carlo sampling results.

     

Biological shielding assessment and dose rate calculation for a neutron inspection portal

With reference to the prototype of neutron inspection portal built and successfully tested in the Rijeka seaport (Croatia) within the EURITRACK (EURopean Illicit Trafficking Countermeasures Kit) project, an assessment of the biological shielding in different set-up configurations of a future portal has been calculated with MCNP Monte Carlo code in the frame of the Eritr@C (European Riposte against Illicit TR@ffiCking) project. In the configurations analyzed the compliance with the dose limits for workers and the population stated by the European legislation is provided by appropriate shielding of the neutron sources and by the delimitation of a controlled area.     

Predicting the Change of MWD Caused by Interchange Reactions During Melt‐Mixing of Linear and Branched Polycondensates (AB2)

During mix melting of hyperbranched AB₂‐ and linear CD‐polycondensates distributive properties are changing by interchange reactions. Two mathematical modeling approaches are presented: (i) Simplified approach of monodisperse population of three‐arm stars undergoing interchange reactions, both analytical and by Monte Carlo simulations, assuming interchange as subsequent scission and recombination of fragments. (ii) Full system of interchange and polycondensation/hydrolysis reactions with Monte Carlo simulations and kinetic model describing reactions of free groups (A, B, C, D) and bonds (AB, CD, BC, AD). MC simulations show that the final molecular weight and branching distribution is attained after 10% of reaction time. The change of structure, from few large fragments to more, smaller ones, is slower.

     

单一颗粒物扫描电镜能谱定量分析方法研究

采用实测标准样品、实际样品与模拟样品相结合的方法,对文献中报导的用于定量分析单一颗粒物化学组成的Casino和Quanta计算程序进行了考察和比较。计算结果表明,在校正颗粒物粒径效应时,Casino程序显示了良好效果。Quanta程序在计算沙尘颗粒物中常见的Na、Mg、A l、S i、P、S、K、Ca、Ti、Fe等元素含量时,取得和Casino程序基本一致结果。     

Applicability study on existing dosimetry systems to high-power Bremsstrahlung irradiation

Applicability of the existing dosimetry systems to high-power Bremsstrahlung irradiation was investigated through a dose intercomparison study, where several dosimeters were irradiated in the dose range 4–12 kGy in identical polyethylene phantoms in a Bremsstrahlung beam obtained from a 5-MeV electron accelerator. Included in the study were alanine dosimeters molded by three different binders, three types of liquid dosimeters—ceric-cerous, dichromate and ethanol-chlorobenzen (ECB), and glutamine powder. The dosimeter responses for Bremsstrahlung radiation were analyzed at the issuing laboratories, and the dose values determined using calibration based on cobalt-60 gamma-ray irradiation. Dose values for all the three dose levels for all dosimetry systems were in good agreement—better than 3%. The results of the study demonstrate that these existing dosimetry systems have a potential for application to high-power Bremsstrahlung irradiation.     

Chain Length Distributions of Polyolefins Made with Coordination Catalysts at Very Short Polymerization Times – Analytical Solution and Monte Carlo Simulation

We developed an analytical solution to describe how the CLD of polymers made with coordination polymerization catalysts vary as a function of time for very short polymerization times before the CLD becomes completely developed. We compared the analytical solution with a dynamic Monte Carlo model for validation, obtaining excellent agreement. Our analytical solution can be used to determine when the steady‐state hypothesis, commonly used in polymerization models, becomes valid as a function of polymer chain length. We also extended our model to describe polymerization with multiple‐site‐type catalysts. Depending on the polymerization kinetic parameters of the different site types on the catalyst, the fully developed CLD is reached through very different intermediate CLDs. This modeling approach, although rather simplified, can be used to interpret results from short polymerization time experiments such as the ones done in stopped‐flow reactors.

     

Radiation field modeling of multi-lamp, homogeneous photoreactors

For modeling and optimization of photoreactors, knowing radiation distribution inside the reactor is essential because the kinetics of photochemical and photocatalytic reactions are strongly dependent on the local incident radiation. In this work, a Monte Carlo multi-lamp radiation model is proposed. The model takes into account the reflection on the surface of the lamps, the refraction in the quartz lamp envelope, as well as the adsorption and the isotropic re-emission of radiation in the mercury vapor of the lamp. To quantify the shadowing effect among the lamps, the effective transmittance through a UV-lamp turned on, a lamp turned off, and a lamp quartz envelope have been measured. For validation purposes, experimental measurements have been performed using one, two, and three lamps. The model predictions show good agreement with the experimental results. Finally, in order to simplify the numerical solution of the model, the validity of assuming the lamps 100% opaque and 100% transparent have been analyzed.     

Field-programmable gate arrays and quantum Monte Carlo: Power efficient coprocessing for scalable high-performance computing

Massively parallel architectures offer the potential to significantly accelerate an application relative to their serial counterparts. However, not all applications exhibit an adequate level of data and/or task parallelism to exploit such platforms. Furthermore, the power consumption associated with these forms of computation renders “scaling out” for exascale levels of performance incompatible with modern sustainable energy policies. In this work, we investigate the potential for field-programmable gate arrays (FPGAs) to feature in future exascale platforms, and their capacity to improve performance per unit power measurements for the purposes of scientific computing. We have focused our efforts on variational Monte Carlo, and report on the benefits of coprocessing with a FPGA relative to a purely multicore system.     

5MeV electron beam facilities in Japan

There are 3 facilities with 5MeV electron beam processing machines in Japan and another one is planned to start operation in 1998. 2 of them are installed by Nissin-High Voltage and the other are by Sumitomo Heavy/Radiation Dynamics. In this report are introduced 2 facilities which we have installed and are operating satisfactorily. The first one was: installed at Radia Industry for irradiation services and the second one for in-house use in a factory of a pharmaceutical plastic container manufacturer, Shinko Chemical. And the second one is available for contract irradiation. The machine in Radia Industry has a comprehensive conveyor system with a turn-over equipment to shoot from the top and the bottom of materials with e-beam and X-ray, and has been successfully operated for many years. The machine in Shinko Chemical is equipped with a unique conveyor system with two conveyor lines under the beam window and the motion of the lines are opposite each other. This conveyor system also has a turn-over equipment like other machines but the direction of turning-over is designed to give the irradiated materials more uniform dose.     

Monte Carlo Simulation of Electron Transport and X-Ray Generation. II. Radiative Processes and Examples in Electron Probe Microanalysis

Theoretical models for Monte Carlo simulation of radiative processes, i.e. bremsstrahlung and characteristic x-ray emission, are presented. Possible strategies for simulating electron transport are briefly described. For mechanisms involving energy loss and angular deflections, difficulties for strict implementation of accurate numerical differential cross sections still remain due to the strong correlations between these variables. Practical solutions for the case of inelastic collisions and bremsstrahlung emission are described. Comparisons of simulation results with experimental data for several problems of interest in electron probe microanalysis are presented.     

Electron density distribution in crystal of polyfluorinated tetraazapentalene based on X-ray diffraction data at 130 K

The electron density distribution in crystal of a new heterocyclic compound, 3,6-(l-H-hexafluoroisopropyl)-2,5-trifiuoromethyl-1,6a,3a,4-tetraazapentalene, has been determined by precision X-ray structural analysis at 130 K. The character and features of the electron distribution in the 10 electron system of the heterocycle have been established using the multipole expansion of the electron density. The charges on the C and N atoms of the heterocycle have been estimated based on X-ray diffraction data.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 495–499, March, 1995.This work was supported by the International Science Foundation (grant No. M1F000).     

Structure of cholest-5-en-3β-oxy-5-bromopentane by single-crystal X-ray diffraction at 130 K

Cholest-5-en-3β-oxy-5-bromopentane (1) and cholest-5-en-3β-oxy-11-bromoundecane (2), key precursors for the synthesis of novel cationic amphiphiles based on cholesterol, have been synthesized and characterized by ¹H-NMR spectroscopy and X-ray crystallography. Thermal disorder and effect of length of the bromoalkyl segment on the crystal structure have been investigated. Possible molecular level explanation of the unusual alternating s-trans–gauche conformation of the bromopentyl side chain of (1) has been presented.     

X-ray diffraction study of zirconia pillared clays

X-ray powder diffraction (XRPD) and X-ray radial electronic distribution density (RED) of initial and zirconia-pillared interlayered clays (Zr-PILC) were studied. After pillaring, the basal (001) spacing was found to increase from 11 Å in the initial clay kept under air to 17.7 Å in Zr-PILC. The structure of zirconium nanopillars was characterized. The interatomic distances with corresponding coordination numbers obtained from the RED curves were close to those in zirconium tetramers.This revised version was published online in December 2005 with corrections to the Cover Date.