Levels Of Energy Deposition Research Articles

In Silico Evaluation of Nanosecond Laser Treatment of Pigmented Lesions Based on Skin Optical Properties Using a Model of Melanosome Disruption Threshold Fluence.

This study aimed to evaluate the efficacy and safety of nanosecond laser treatment of pigmented lesions in silico using a model of melanosome disruption threshold fluence (MDTF) based on skin optical properties. Particle size analysis and scanning electron microscopy were performed to determine the threshold fluence for melanosome disruption using a nanosecond laser. By inputting the obtained threshold fluence into the MDTF model and considering the variability in skin optical properties, irradiation parameters were calculated and compared with the results from clinical studies. The threshold fluences for 532 and 755 nm nanosecond laser irradiation were determined to be 3.0 and 15.0 J/cm2, respectively. In silico analysis showed that the incident fluence for moderately pigmented skin should be 1.2 times that for lightly pigmented skin, whereas it should be 50% lower than that for lightly pigmented skin to achieve the same level of energy deposition. Clinically applied fluences for moderately pigmented skin are at the low end of the calculated range of values, suggesting that the clinical fluence is chosen to minimize energy deposition in normal tissues. Our results showed that the MDTF model can be used to evaluate nanosecond laser treatments and provide clinical guidance on fluence settings based on laser-tissue interactions in moderately pigmented skin. The in silico method can, therefore, provide a robust and quantitative retrospective evaluation of the treatment effects that accounts for variation in irradiation parameters among patients by combining the MDTF model with the in vivo optical properties of individual skin types.

Density profile of 3He in a nanoscale 3He-4He superfluid film determined by neutron scattering

For decades, superfluid helium has attracted the interest of the scientific community as an extremely pure realisation of a quantum liquid, only accessible at temperatures close to absolute zero. Previously, helium films have only been observed directly using X-rays. However, this method is limited to temperatures above 1 K due to the high levels of energy deposition, and it also suffers from an inability to distinguish between helium isotopes. Here we show that a 3He layer on top of a phase separated mixture film at 170 mK gradually dissolves into the 4He with increasing temperature. We also observe an anomaly in film behaviour near 300 mK and unexpected restoration of the layered structure at 1.5 K which is consistent with a re-entrant phase transition leading to the suppression of superfluidity in the film near 300 mK. Our successful application of neutron scattering to study helium films at ultra-low temperatures opens up new possibilities for future research.

Corner T-slot antenna at 2.45 GHz for hyperthermia application

ABSTRACT This study focuses on the design and characterization of a novel T-slot antenna for hyperthermia application at 2.45 GHz. The simulation and experimental results demonstrate that the antenna has a resonant frequency of 2.45 GHz, is found to be in good agreement and a gain of −5.1 dBi. The proposed antenna has a dimension of 26 × 26 × 1.6 mm3 with 2.85% BW. The antenna's surface current distribution and specific absorption rate (SAR) are analyzed using numerical simulations, and the results show that the antenna provides an effective heating pattern with low levels of energy deposition in the surrounding healthy tissue. Finally, a proof-of-concept hyperthermia treatment is performed on a tissue-equivalent-liquid (TEL) phantom using the proposed antenna. The proposed T-slot antenna has the potential for use in hyperthermia treatments for cancer therapy, and further studies are required to evaluate its safety and efficacy for clinical use.

Acoustic characteristics of laser-induced plasmas from the forming dynamics perspective

The acoustic signal has demonstrated its capabilities in assisting laser-induced breakdown spectroscopy (LIBS) measurements. In this study, the acoustic characteristics of laser-induced plasmas (LIPs) under different levels of energy deposition were analyzed, and their correlation with LIP forming dynamics was investigated. In the deposited energy space, two zones in the acoustic pressure and duration were observed, featuring a clear transition point in 100 mJ. The analysis based on self-emission spectra and images suggested that this transition is a result of the change in plasma forming dynamics. Above 100mJ, the plasma temperature and electron density were saturated; thus, any further increase in deposited energy only contributes to the plasma size. In this regime, the acoustic wave from the significantly elongated plasma no longer satisfied the ideal spherical assumption. The observation was also strengthened by the analysis in the frequency domain. Moreover, the correlation between acoustic and radiation signals was also changed significantly with plasma forming dynamics. This study offers a systematic analysis of LIP acoustic signals on the deposited energy space. The potential of using acoustic measurement to interpret the plasma forming dynamics was demonstrated, which could be beneficial for the successful implementations of acoustic-aided LIBS.

ISUOG Practice Guidelines (updated): performance of fetal magnetic resonance imaging.

ISUOG Practice Guidelines (updated): performance of fetal magnetic resonance imaging.

A Comprehensive Analysis of Radiosensitization Properties of Metallic Nanoparticles in Brachytherapy of Gastric Adenocarcinoma by I-125 Seed: A Simulation Study by MCNPX and MCNP6 Codes

Purpose: In the current study, we aimed to look into the macroscopic and microscopic dose enhancement effect of metallic nanoparticles in interstitial brachytherapy of gastric adenocarcinoma by Iodine-125 source using a nano-lattice model in MCNPX (2.7) and MCNP6.1 codes. Materials and methods: Based on a nano-lattice simulation model containing a radiation source and a tumor tissue with cellular compartments loaded with 7 mg/g spherical nanoparticles, the microscopic and macroscopic levels of energy deposition by the secondary electrons was estimated. Results: The results show that the values of macroscopic DEF are higher than microscopic DEF values and the macroscopic DEF values decrease by increasing the distance from the surface of brachytherapy source. Accordingly, it could be noted that gold nanoparticles have the highest radiosensitization effect among the other nanoparticles and the related DEF value is close to the resultant DEF values for bismuth nanoparticles. Moreover, the results revealed a remarkable discrepancy between the DEF and secondary electron spectra calculated by MCNPX (2.7) and MCNP6.1 codes, which could be justified by the difference in energy cut-off and electron transport algorithms of two codes. Conclusions: According to the both MCNPX (2.7) and MCNP6.1 outputs, it could be concluded that the presence of metallic nanoparticles in the tumor tissue of gastric adenocarcinoma increases the physical effectiveness of brachytherapy by I-125 source. This study aims to provide recommendations for future preclinical studies. Actually, the results presented herein give a physical view of radiosensitization potential of different metallic nanoparticles and could be considered in design of analytical and experimental radiosensitization studies in tumor regions using various radiotherapy modalities in the presence of heavy nanomaterials.

Mechanism of nonequilibrium plasma-enhanced ignition in the event of dual-pulse laser energy deposition

A two-dimensional (2D) and three-temperature mathematical model for dual-pulse laser (DPL) ignition was applied to study the mechanism of the nonequilibrium plasma (NEQP) process during DPL energy deposition. The 2D model could predict the influence of the reaction kinetics and nonequilibrium effects on the ignition delay time and kernel dynamics. As the plasma reaction rates were extremely fast compared with the combustion reaction rates, it can be predicted that the variability of the plasma lifetime will directly influence the ignition delay time and reaction kinetics. The results suggested that the energy relaxation rate from the electronic state was rapid compared to that from the vibrational state due to the short lifetime of the plasma state. However, the relatively slower energy relaxation from the vibrational state provided long-term thermalization of the ignition kernel. For the same level of energy deposition, the NEQP system predicted a higher rate of vorticity generation, signifying a higher level of mixing and baroclinicity production. The results also suggested that ignition in a premixed fuel airflow required a higher degree of energy deposition, due to a higher rate of radical and thermal losses.

Characterization of the beam scraping system of the CERN Super Proton Synchrotron

The Super Proton Synchrotron at CERN is equipped with a scraping system for halo cleaning at beam transfer to the Large Hadron Collider. The system is composed of movable graphite blades mechanically swept through the beam to remove tails immediately before beam transfer. Due to the mechanical movement, beam particles are intercepted by a small volume of material with consequent concentration of energy deposition and high thermal loads. The blades were tested with beam to verify their resistance to the most extreme scraping conditions. Even though the beam was prematurely dumped by the beam loss monitoring system, the microstructural analysis of the blades following the test found signs of material sublimation. The test setup was reproduced in simulation to reconstruct the levels of energy deposition actually reached in the blades during the test; values are compatible with local material sublimation, in agreement with the microstructural analysis. Simulations were carried out by coupling the sixtrack tracking code, used for single particle beam dynamics in circular accelerators for high energy physics, to the fluka Monte Carlo code, for particle-matter interactions. The time evolution of the beam intensity measured during scraping and the distribution of losses around the ring were used for an extensive benchmark of the simulation tool against measurements taken during the test. This work presents the endurance test together with simulation results and the benchmark of the simulation tool. The quantitative agreement between simulations and measurements proves the quality of the analyses and the maturity of the simulation tool, which can be reliably used to predict the performance of cleaning systems in circular accelerators.

The early stage of the thermal pulse explosions of aluminum nanowires under different energy deposition levels

Molecular dynamics simulations are performed to study the initial stage of the electrical explosions of Al nanowires in vacuum. The radial difference of wire expansion rate was observed in the early stages of the explosions. It is found that the wire radial expansion rate and the thermodynamic parameters interact with each other. We studied the time-varying thermodynamic parameters in the matched mode expansions, obtained the phase trajectories of wire material. Our results proved that the energy deposition levels dominate the explosion regime: when the energy ratio is less than 0.208, wire expansion will not develop into an explosion; phase explosion occurs under an underheated condition; supercritical explosion generally happens when the energy deposition is greater than the sublimation energy. We tracked the transformation trajectory of the deposited energy and found it is not preferentially transformed into the internal energy but simultaneously transformed into the explosion kinetic energy. As a result, even for the deposited energy reaching or exceeding the sublimation energy, material cannot be fully gasified. Finally, the deposition energy consumed by the internal energy has an upper limit: the sublimation energy.

Non-diffusive ignition of a gaseous reactive mixture following time-resolved, spatially distributed energy deposition

Systematic asymptotic methods are applied to the compressible conservation and state equations for a reactive gas, including transport terms, to develop a rational thermomechanical formulation for the ignition of a chemical reaction following time-resolved, spatially distributed thermal energy addition from an external source into a finite volume of gas. A multi-parameter asymptotic analysis is developed for a wide range of energy deposition levels relative to the initial internal energy in the volume when the heating timescale is short compared to the characteristic acoustic timescale of the volume. Below a quantitatively defined threshold for energy addition, a nearly constant volume heating process occurs, with a small but finite internal gas expansion Mach number. Very little added thermal energy is converted to kinetic energy. The gas expelled from the boundary of the hot, high-pressure spot is the source of mechanical disturbances (acoustic and shock waves) that propagate away into the neighbouring unheated gas. When the energy addition reaches the threshold value, the heating process is fully compressible with a substantial internal gas expansion Mach number, the source of blast waves propagating into the unheated environmental gas. This case corresponds to an extremely large non-dimensional hot-spot temperature and pressure. If the former is sufficiently large, a high activation energy chemical reaction is initiated on the short heating timescale. This phenomenon is in contrast to that for more modest levels of energy addition, where a thermal explosion occurs only after the familiar extended ignition delay period for a classical high activation reaction. Transport effects, modulated by an asymptotically small Knudsen number, are shown to be negligible unless a local gradient in temperature, concentration or velocity is exceptionally large.

Three-Dimensional ‘Textured’ Coatings as First-Wall Materials: Exposure to Energetic Ions on RHEPP-1

The level of energy deposition on future inertial fusion energy (IFE) reactor first walls, particularly in direct-drive scenarios, makes the ultimate survivability of such wall materials a challenge. We investigate the survivability of three-dimensional (3-D) dendritic materials fabricated by chemical vapor deposition (CVD), and exposed to repeated intense helium beam pulses on the RHEPP-1 facility at Sandia National Laboratories. Prior exposures of flat materials have led to what appears to be unacceptable mass loss on timescales insufficient for economical reactor operation. Two potential advantages of such dendritic materials are a) increased effective surface area, resulting in lowered fluences to most of the wall material surface, and b) improvement in materials properties for such micro-engineered metals compared to bulk processing. Several dendritic fabrications made with either tungsten and tungsten with rhenium show little or no morphology change after up to 800 pulses of 1 MeV helium at reactor-level thermal wall loading. Since the rhenium is added in a thin surface layer, its use does not appear to raise environmental concerns for fusion designs.

Calculation of attainable superheats and predicted embryonic flux rates in commercial water isotope targets

Phase change in a fluid subject to a large spectrum of radiations is examined. The statistical variation in the fluid energy is considered in concert with the radiation field attributes to establish conditions for spinodal decomposition and bulk nucleation. This approach is developed in general and carried forward for the specific case of 18O-enriched water used in commercial targets for the production of 18F. Sensitivities of the outcome to specific attributes of the fluid state model are examined. The possibility for very high bulk nucleation site densities is exposed and may explain the observed thermal-fluid behavior in commercial water targets. These targets operate at elevated pressure and temperatures at and in excess of the saturation temperature. They are also subjected to a large spectrum of radiations, with differing levels of energy deposition. The conditions for spinodal decomposition and bulk nucleation (with and without radiation) in these targets are evaluated. It is likely that some bulk nucleation is occurring, and causing the density reduction locally in the target. Suitable experiments to evaluate this potential are more fully possible.

Numerical simulation of capillary plasma flow generated by high-current pulsed power

Pulsed plasma discharge in the interior region of electrothermal–chemical gun is numerically investigated with the one-dimensional time-dependent mathematical modeling that includes the Joule heating of plasma column and the mass ablation of bore wall. Sonic boundary condition is utilized because flow is expected to be choked at the bore exit. In the evaluation of thermodynamic and transport properties, plasma state is assumed to be in local thermal equilibrium due to high pressure and is found to be weakly nonideal. The computational results show that capillary plasma flow at the bore exit is partially ionized high temperature and high pressure discharge. Many predicted data including arc resistance, energy deposition, and bore wall mass ablation are favorably compared with the measurements on total 8 shots of gun firings with different levels of energy deposition ranging from 5.3 to 47 kJ. Temporal evolution of pressure shows transient effect in the calculations but the effect is minimal compared to the significant transient effect in the pressure measurements. However, maximum pressure is in good agreement with measured data.

A massive bolometer on the international space station to measure energy deposition by the space radiation environment

We describe a novel space-based low-temperature radiation detector, the “Particle Heating Detector” (PhD), which was recently selected to be part of the first mission of the Low-Temperature Microgravity Physics Facility, scheduled to fly on the International Space Station in 2008. This massive bolometer will measure total heating induced in an aluminum absorber by the space radiation environment. The use of paramagnetic alloy thermometers with SQUID readout, giving 0.3nK/Hz resolution, combined with a large-area absorber, will enable the detector to perform high-resolution, real-time measurement of the low energy deposition levels caused by galactic cosmic rays in low-Earth orbit.

Elastographic characterization of HIFU-induced lesions in canine livers

The elastographic visualization and evaluation of high-intensity focused ultrasound (HIFU)-induced lesions were investigated. The lesions were induced in vitro in freshly excised canine livers. The use of different treatment intensity levels and exposure times resulted in lesions of different sizes. Each lesion was clearly depicted by the corresponding elastogram as being an area harder than the background. The strain contrast of the lesion/background was found to be dependent on the level of energy deposition. A lesion/background strain contrast between −2.5 dB and −3.5 dB was found to completely define the entire zone of tissue damage. The area of tissue damage was automatically estimated from the elastograms by evaluating the number of pixels enclosed inside the isointensity contour lines corresponding to a strain contrast of −2.5, −3 and −3.5 dB. The area of the lesion was measured from a tissue photograph obtained at approximately the same plane where elastographic data were collected. The estimated lesion areas ranged between approximately 10 mm 2 and 110 mm 2. A high correlation between the damaged areas as depicted by the elastograms and the corresponding areas as measured from the gross pathology photographs was found (r 2 = 0.93, p value < 0.0004, n = 16). This statistically significant high correlation demonstrates that elastography has the potential to become a reliable and accurate modality for HIFU therapy monitoring.

Evidence for atomic mixing induced in metallic bilayers by electronic energy deposition

High levels of energy deposition by electronic excitations can induce damage creation in some bulk metallic targets as soon as the rate of energy deposition in electronic excitation is higher than a few 10 keV/nm. The present study is aimed at determining whether such excitations can also induce interdiffusion at the interface of metallic bilayers. Ni Ti bilayers were irradiated at 80 K with GeV Pb, Ta and U ions up to a few 10 13 ions/cm 2. Damage creation and mixing were followed using various methods: electrical resistance, grazing X-ray and neutron reflectometry, X-ray diffraction, electron microscopy and electron energy loss on target cross-sections. A very strong mixing is indeed observed at the Ni Ti interface as a result of electronic energy deposition: the observed mixing efficiency is at least two orders of magnitude higher than that induced by elastic collisions with target nuclei. We finally study the influence of various parameters (irradiation temperature, symetry of the interface) on the mixing efficiency and follow the kinetics of the mixing process.

Factors affecting extended hydration depths in ion-implanted fused silica

The implantation of fused silica to high collisional energy deposition levels allows penetration of hydrogenic species, either from aqueous solutions or atmospheric ambients, to depths exceeding the theoretical ranges by a factor of 2–3. In the case of ambient exposure, hydration is known to persist over periods of years after implantation. Extended depths are also seen for etching, gaseous implant distribution, and alkali depletion. The phenomena are examined using the modeling of strained silica structures as the driving force for slow fracture and the extensive structural understanding provided by sol-gel investigations.

Atomic mixing induced in metallic bilayers by high electronic excitations

It has been recently established that high levels of energy deposition in electronic excitations can induce damage creation in a few metallic targets as soon as the linear rate of energy deposition in electronic excitation is of the order of a few 10 keV/nm. The present study is aimed at determining whether high electronic excitations can induce interdiffusion at the interface of metallic bilayers. Ni Ti bilayers were irradiated at 80 K with GeV Ta ions up to a few 10 13 ions/cm 2. Damage creation and mixing were followed using various methods: X-ray and neutron reflectometry, X-ray diffraction, electron microscopy and electron energy loss on transverse cuts. A very strong mixing is observed at the Ni Ti interface as a result of high electronic excitations.

Evolution of microstructure resulting from high electronic excitation during swift heavy ion irradiations

This paper is devoted to the specific damage processes resulting from high levels of energy deposition in electronic excitation (a few 10 keV/nm) in metallic targets. Such conditions are fulfilled during irradiations with GeV heavy ions. After a short discussion about the mechanisms of energy deposition in elastic and inelastic collisions, the various microstructural changes observed during swift heavy ion irradiations of metals are described. The damage resulting from electronic excitation is localized along the ion wake and consists mainly in local or long-range order modifications or even phase transformation in crystalline materials and in anisotropic growth in amorphous materials. A tentative model based on the Coulomb explosion mechanism explains how part of the energy deposited in electronic excitation can be transferred to lattice atoms and accounts for the available experimental results.

α→ω phase transformation induced in titanium during ion irradiations in the electronic slowing-down regime

Abstract This letter shows that the displacive phase transformation from the h.c.p. α-phase to the hexagonal co-phase can be triggered in titanium targets in an unusual way during swift heavy ion irradiations. This unexpected result is a consequence of the high level of energy deposition in electronic excitation. A model based on the Coulomb explosion mechanism can account for such a phase transformation.