Spatial resolution characteristics of a-Se imaging detectors using Monte Carlo methods with detailed spatiotemporal transport of x-rays, electrons, and electron-hole pairs under applied bias

Determinations of spatial X-ray resolution in conventional microanalysis in electron probe microanalysers where the beam is perpendicular to a smooth surface are now quite straightforward. However, SEM's and STEM'S are becoming increasingly used methods for performing microanalysis. The specimen arrangement for this sort of work often involves both inclined beam and detector geometries. Under these conditions X-ray correction constants have to be altered due to the changed average path length for the emerging X-rays. The spatial resolution and correction constants peculiar to the new geometry can be physically studied using a Monte Carlo computer method which simulates the trajectories of many electrons as they interact with the specimen.Another attempt to predict resolution and effective take-off angle using single electron scattering theory has been made for thin films. This over estimates the X-ray source size at large foil thicknesses and under estimates at small foil thicknesses. Experimental methods have been devised utilising edges and small, spherical particles.

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Study of Tissue Inhomogeneity Effects on Central Axis Radiation Beam Parameters using Monte Carlo Methods

International Journal of Medical Research and Review ◽

10.17511/ijmrr.2020.i05.03 ◽

2020 ◽

Vol 8 (5) ◽

pp. 352-362

Author(s):

Dr. Santhosh VS ◽

◽

Dr. Anand RK ◽

Keyword(s):

Monte Carlo ◽

Monte Carlo Methods ◽

Homogeneous Medium ◽

Central Axis ◽

Beam Parameter ◽

Monte Carlo Code ◽

X Rays ◽

Radiation Beam ◽

Beam Parameters ◽

Tissue Inhomogeneity

Introduction: The central axis radiation beam parameters are used for the dose calculations inradiotherapy and usually measured in a homogeneous medium. Human body is not homogeneous innature and the incident beam has to travel through different medium such as bone tissue air etc toreach the tumor. Objective: The objective of the present work is to study the effects of tissueInhomogeneity on central axis beam parameter such as percentage Depth Dose using Monte CarloMethods Materials and Methods: The Monte Carlo simulation is a virtual experiment and can beconducted with the Monte Carlo software tool installed in a PC. Input files are written as per thespecification of the Monte Carlo code. Two radiation beams beans commonly used for radiationtreatment such as Cobalt 60 and 6MV X ray were used for the simulation. Results: Depth Dosecharacteristics in homogeneous tissue medium for Cobalt60 and 6MV X rays beams were studied andis consistent with the published experimental values.In the second case, at the interface betweentissue and bone the PDD pattern changed as reported by the previous works. And the absorbed doseat bone layer is higher than the dose value predicated in a homogeneous condition. In the nextsimulation we conducted the simulation for a tissue air tissue medium. Conclusion: The presentstudy clearly demonstrate that Monte Carlo methods simulation can be used as a tool for estimationof dose in tissue Inhomogeneity where measurements are seldom possible.

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High spatial resolution x-ray microanalysis of interfaces

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100137793 ◽

1995 ◽

Vol 53 ◽

pp. 284-285

Author(s):

J. R. Michael

Keyword(s):

Spatial Resolution ◽

Electron Probe ◽

Solid Angle ◽

Collection Efficiency ◽

Spatial Scales ◽

Energy Dispersive Spectrometer ◽

X Rays ◽

X Ray ◽

Probe Size ◽

Brightness Field

X-ray microanalysis in the analytical electron microscope (AEM) refers to a technique by which chemical composition can be determined on spatial scales of less than 10 nm. There are many factors that influence the quality of x-ray microanalysis. The minimum probe size with sufficient current for microanalysis that can be generated determines the ultimate spatial resolution of each individual microanalysis. However, it is also necessary to collect efficiently the x-rays generated. Modern high brightness field emission gun equipped AEMs can now generate probes that are less than 1 nm in diameter with high probe currents. Improving the x-ray collection solid angle of the solid state energy dispersive spectrometer (EDS) results in more efficient collection of x-ray generated by the interaction of the electron probe with the specimen, thus reducing the minimum detectability limit. The combination of decreased interaction volume due to smaller electron probe size and the increased collection efficiency due to larger solid angle of x-ray collection should enhance our ability to study interfacial segregation.

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Low-voltage EDS of magnesium ferrite Dendrites in a FEG-SEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100164854 ◽

1996 ◽

Vol 54 ◽

pp. 478-479

Author(s):

Matthew T. Johnson ◽

Ian M. Anderson ◽

Jim Bentley ◽

C. Barry Carter

Keyword(s):

Monte Carlo ◽

Quantitative Analysis ◽

Monte Carlo Simulations ◽

Cross Section ◽

Spatial Resolution ◽

Low Voltage ◽

Magnesium Ferrite ◽

X Ray ◽

Interaction Volume ◽

Ferrite Spinel

Energy-dispersive X-ray spectrometry (EDS) performed at low (≤ 5 kV) accelerating voltages in the SEM has the potential for providing quantitative microanalytical information with a spatial resolution of ∼100 nm. In the present work, EDS analyses were performed on magnesium ferrite spinel [(MgxFe1−x)Fe2O4] dendrites embedded in a MgO matrix, as shown in Fig. 1. spatial resolution of X-ray microanalysis at conventional accelerating voltages is insufficient for the quantitative analysis of these dendrites, which have widths of the order of a few hundred nanometers, without deconvolution of contributions from the MgO matrix. However, Monte Carlo simulations indicate that the interaction volume for MgFe2O4 is ∼150 nm at 3 kV accelerating voltage and therefore sufficient to analyze the dendrites without matrix contributions.Single-crystal {001}-oriented MgO was reacted with hematite (Fe2O3) powder for 6 h at 1450°C in air and furnace cooled. The specimen was then cleaved to expose a clean cross-section suitable for microanalysis.

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