Monte Carlo simulation of plasma oscillations in ultra-thin layers

2008 ◽  
Vol 5 (1) ◽  
pp. 249-252 ◽  
Author(s):  
J.-F. Millithaler ◽  
L. Varani ◽  
C. Palermo ◽  
J. Pousset ◽  
W. Knap ◽  
...  
1975 ◽  
Vol 19 ◽  
pp. 323-337 ◽  
Author(s):  
A. R. Hawthorne ◽  
R. P. Gardner ◽  
T. G. Dzubay

Monte Carlo simulation is used to determine the effects of selfabsorption for the low energy X-rays of light elements in the size range front 1 to 20 μm. Calculations are performed for a wide angle Fe-55 radioisotope-excited energy dispersive XRF system. Results are obtained for sulfur attenuation in thin layers, long cylinders, and spheres composed of various matrix materials. The enhancement effect is also treated for the transition region between thin and thick layer samples as well as in spheres of various sizes. Results are also comrpared to fixed angle analytical models.


Author(s):  
Reginald Eze ◽  
Anisur Rahman ◽  
Sunil Kumar

A Monte Carlo model with special features for modeling of radiation transport through very thin layers has been presented. Over the decades traditional Monte Carlo model has been used to model highly scattering thin layers in skin and may inaccurately capture the effect of thin layers since their interfaces are not perfectly planar and thicknesses non-uniform. If the Monte Carlo model is implemented without special features then the results of the simulation would show no effect of the outer thin layer since the path length of most photons would be significantly larger than the layer thickness and the resulting predicted photon travel would simply not notice the presence of the layer. Examples of multi-layered media are considered where the effect of a very thin absorbing layers is systematically examined using both the traditional Monte Carlo and that with new features incorporated. The results have profound implications in the diagnostic and therapeutic applications of laser in biomedicine and surgery.


Author(s):  
Reginald C. Eze

Radiative-thermal models of light transport in tissue are presented that stimulates the thermal effects of pulsed laser radiation on very thin scattering and absorbing biological layers. Thermal therapies require a firm understanding of temperature-depth relationship for tissue modification or destruction, especially through very thin layers that are characterized by contrasting opto-thermal properties. Temperature distribution in biological layers of thicknesses in the order of their mean free path or less are evaluated before the onset of thermal diffusion for both the traditional model of Monte Carlo simulation and that with new features tailored for very thin layers. Temperature dynamics in very thin layers such as skin in dermatology is a typical example. For instance, during the heating of small volumes of tissue as in fractional photothermolysis, nonablative dermal remodeling and ablative skin resurfacing, short pulse lasers are used by choosing pulse length sufficiently short that will not damage the surrounding healthy tissue, but sufficiently long enough to allow damage, necrosis or coagulation over the entire target area. This is in contrast to the situation where thermal dissipation due to heat conduction is the principal determinant of tissue damage. Numerical results obtained from both models differ significantly. While the model designed specifically for very thin scattering layers tends to confine temperature rise to specific layers, the traditional model have a tendency to misjudge the layers of interest thereby giving rise to temperature increase in undesired locations. These results will advance our understanding of radiation transport in layers that are extremely very thin, and help develop better treatment modules for laser therapeutic treatment regimes in surgery and dermatology.


Author(s):  
R. Eze ◽  
Y. Hassebo

Monte Carlo simulation of photon transport is formulated to solve transient radiative transfer equation through thin multilayered scattering-absorbing media with inhomogeneous properties. Though thin layers might seem to be geometrically insignificant, contribution of their radiative properties is relevant in predicting the behavior of most bioengineering, biomedical and space applications. Most traditional Monte Carlo models often fail to capture the presence of thin layers and account for its radiative properties. If the Monte Carlo model is implemented without unique features then the results of the simulation would show incorrect effect of thin layers since the path length of most photons would be significantly larger than the layer thickness and the evaluated photon travel path length would simply not feel the existence of the layer. Numerical and algorithmic features for computation of radiation transport through thin scattering and absorbing layers using the traditional Monte Carlo and an enhanced Monte Carlo model with features specifically developed for thin layers is presented and implemented for the analysis of backscattered radiation. It is observed that while Monte Carlo without special features defines the radiative effect of the layers, the refined technique indicates that layers have a great impact on the backscattered light, especially if the layer properties are distinctly different from those of the contiguous layers. The results have significant implications in the study of diagnostic applications of laser in biomedical applications since backscattered light is one of the non-invasive techniques available for detection of diseases and complements other known methods. Analyses of backscattered signals have also found use in the noninvasive methods of medical use especially in skin diagnostics.


Author(s):  
Ryuichi Shimizu ◽  
Ze-Jun Ding

Monte Carlo simulation has been becoming most powerful tool to describe the electron scattering in solids, leading to more comprehensive understanding of the complicated mechanism of generation of various types of signals for microbeam analysis.The present paper proposes a practical model for the Monte Carlo simulation of scattering processes of a penetrating electron and the generation of the slow secondaries in solids. The model is based on the combined use of Gryzinski’s inner-shell electron excitation function and the dielectric function for taking into account the valence electron contribution in inelastic scattering processes, while the cross-sections derived by partial wave expansion method are used for describing elastic scattering processes. An improvement of the use of this elastic scattering cross-section can be seen in the success to describe the anisotropy of angular distribution of elastically backscattered electrons from Au in low energy region, shown in Fig.l. Fig.l(a) shows the elastic cross-sections of 600 eV electron for single Au-atom, clearly indicating that the angular distribution is no more smooth as expected from Rutherford scattering formula, but has the socalled lobes appearing at the large scattering angle.


Author(s):  
D. R. Liu ◽  
S. S. Shinozaki ◽  
R. J. Baird

The epitaxially grown (GaAs)Ge thin film has been arousing much interest because it is one of metastable alloys of III-V compound semiconductors with germanium and a possible candidate in optoelectronic applications. It is important to be able to accurately determine the composition of the film, particularly whether or not the GaAs component is in stoichiometry, but x-ray energy dispersive analysis (EDS) cannot meet this need. The thickness of the film is usually about 0.5-1.5 μm. If Kα peaks are used for quantification, the accelerating voltage must be more than 10 kV in order for these peaks to be excited. Under this voltage, the generation depth of x-ray photons approaches 1 μm, as evidenced by a Monte Carlo simulation and actual x-ray intensity measurement as discussed below. If a lower voltage is used to reduce the generation depth, their L peaks have to be used. But these L peaks actually are merged as one big hump simply because the atomic numbers of these three elements are relatively small and close together, and the EDS energy resolution is limited.


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