Effect Of Pulsed Irradiation Research Articles

10W半導体レーザーのパルス照射が圧痛閾値と時間的加重に与える影響

10W半導体レーザーのパルス照射が圧痛閾値と時間的加重に与える影響

Temperature field simulation of chalcogenide glass ablation by nanosecond pulsed laser-based on pump–probe technology

Chalcogenide glass (ChG) is one of the best candidate materials for the fabrication of micro-nano resolution photonic devices by laser direct writing (LDW). In this work, the thermodynamics and the surface structures evolution of As2S3 by nanosecond pulse are investigated by the dual-laser pump–probe system. Above the ablation threshold (124, 157, 196 mJ/cm2), the descend duration of sample surface reflectivity was observed to be 25, 48, and 80 ns, respectively. Furthermore, to research the effects of pulse irradiation and surface thermal energy diffusion on the sample surface temperature, the dual-temperature model is applied. At the lowest laser fluence, the temperature drops rapidly to the melting point in a short time (23 ns), which results in the formation of a crater in the pulse action area. At the highest fluence, the surface temperature decreases slowly to the melting point (77 ns). And during this period, the material surface is continuously heated, which leads to the deepening of melting depth. So, a deep crater (294 nm) is formed on the surface, and the reflectivity declines the slowest. Secondly, due to the highest temperature in the central region and the diffusion movement of heat energy, the rim structure and the small droplet structures will appear at a higher fluence.

UV pulsed irradiation effect on the exciton luminescence of CuCl nanocrystals in borate glass

Heat treatment conditions effect on the characteristics of the Z3-exciton resonant luminescence of CuCl nanocrystals in potassium-aluminaborate glass is studied. The observed patterns of luminescence buildup are explained by the participation of thermal effects in recombination processes. The size effect in the resonance emission of Z3-excitons at 80 K is confirmed. The inverse dependence of the defectiveness of CuCl crystals in glass on the luminescence buildup rate of Z3-excitons is established.

Effect of pulse irradiation on the evolution of damage structure

Charged particle beams from accelerators driven by radiofrequency or with beam scanners possess time structures (i.e., pulse beam operations). However, it is not clear whether the irradiation effects of these pulse beam operations are the same as those of continuous beams, although the average damage rate is the same in both cases. In this study, the difference between continuous beams and pulse beams, and the effect of the repetition frequency and pulse duration on the defect accumulation are evaluated by the rate equation analysis for Al and Fe. The growth rate of interstitial type dislocation loops in Al is simulated with fixed duty ratios (constant pulse duration over the irradiation period) at 453 K. The effect of pulse duration on a constant period of 1 s is simulated in Fe, changing the pulse duration from 1 to 10−6 s, while the damage (dpa) caused by one pulse remains the same. The results are analyzed and the effects of pulse duration and repetition rate on the damage structure evolution are demonstrated in relation to materials parameters.

Immediate Effect of Pulse Irradiation with a 10-W Semiconductor Laser on Current Perception Threshold and Current Pain Threshold

Immediate Effect of Pulse Irradiation with a 10-W Semiconductor Laser on Current Perception Threshold and Current Pain Threshold

STUDY OF THE INFLUENCE OF THE SPECTRAL COMPOSITION OF IR RADIATION ON THE SEDIMENTATION RATE OF COMPLEX COMPOUNDS

The aim of this work is to study the effect of pulsed IR radiation generated by functional ceramics and cavitation on the processes of sedimentation and coagulation of extremely fine fractions. It is shown that these methods are complementary for solving technological problems.

Hundred joules plasma focus device as a potential pulsed source for in vitro cancer cell irradiation

Plasma focus devices may arise as useful source to perform experiments aimed to study the effects of pulsed radiation on human cells in vitro. In the present work, a table top hundred joules plasma focus device, namely “PF-400J”, was adapted to irradiate colorectal cancer cell line, DLD-1. For pulsed x-rays, the doses (energy absorbed per unit mass, measured in Gy) were measured using thermoluminescence detectors (TLD-100 dosimeters). The neutron fluence and the average energy were used to estimate the pulsed neutron doses. Fifty pulses of x-rays (0.12 Gy) and fifty pulses of neutrons (3.5 μGy) were used to irradiate the cancer cells. Irradiation-induced DNA damage and cell death were assessed at different time points after irradiation. Cell death was observed using pulsed neutron irradiation, at ultralow doses. Our results indicate that the PF-400J can be used for in vitro assessment of the effect of pulsed radiation in cancer cell research.

Short and long-term phototoxicity in cells expressing genetic reporters under nanosecond laser exposure

Nanosecond-duration laser pulses are exploited in a plethora of therapeutic and diagnostic applications, such as optoacoustic imaging. However, phototoxicity effects of pulsed radiation in living cells, in particular those expressing genetic reporters, are not well understood. We established a three-dimensional fluorescent protein expressing cellular model in order to reliably investigate the extent and major exposure parameters responsible for both photobleaching and phototoxicity under pulsed laser exposure, unveiling a variety of possible effects on living cells, from reversible photobleaching to cytotoxicity and cell death. Significant losses of fluorescence levels were identified when exposing the cells to illumination conditions considered safe under common standards for skin exposure in diagnostic imaging applications. Thus, the use of photolabile fluorescent proteins and their in vivo exposure parameters have to be designed carefully for all applications using pulsed nanosecond radiation. In particular, loss of signal due to bleaching may significantly alter signals in longitudinal measurements, making data quantification challenging.

Mechanical properties of carbon steel depending on the rate of the dose build-up of nitrogen and argon ions

The effect of pulsed irradiation with argons and nitrogen ions on the mechanical properties, mor� phology, and structure of the surface layers of carbon steel St3 (0.2% C, 0.4% Mn, 0.15% Si, and Fe for bal� ance) has been investigated depending on the rate of dose buildup at an average ion current density of 10, 20, and 40 μA/cm 2 . It has been established that the fatigue life and microhardness of surface layers increase in the entire studied range of dose buildup rates. This seems to be due to the hardening of the surface layers, which resulted from the generation of radiation defects and the irradiationdynamic effect of fast ions. The sample irradiated by argon ions at the lowest of the selected dose buildup rates j av = 10 μA/cm 2 withstands the largest number of cycles to failure.

Evolution of the structure of plasma metal-ceramic coating under pulsed electron-beam treatment

The effect of pulsed irradiation with a high-power electron beam on the structure of plasma metal-ceramic coatings sprayed from TiC-(Ni-Cr) composite powders is investigated. It is found that the coatings are heated until melting under high-power pulsed electron beam irradiation. With an increase in the size of the powder composite particles sprayed, the efficiency of heating of the coating layer increases.

Radiation induced currents in MRI RF coils: application to linac/MRI integration

The integration of medical linear accelerators (linac) with magnetic resonance imaging (MRI) systems is advancing the current state of image-guided radiotherapy. The MRI in these integrated units will provide real-time, accurate tumor locations for radiotherapy treatment, thus decreasing geometric margins around tumors and reducing normal tissue damage. In the real-time operation of these integrated systems, the radiofrequency (RF) coils of MRI will be irradiated with radiation pulses from the linac. The effect of pulsed radiation on MRI radio frequency (RF) coils is not known and must be studied. The instantaneous radiation induced current (RIC) in two different MRI RF coils were measured and presented. The frequency spectra of the induced currents were calculated. Some basic characterization of the RIC was also done: isolation of the RF coil component responsible for RIC, dependence of RIC on dose rate, and effect of wax buildup placed on coil on RIC. Both the time and frequency characteristics of the RIC were seen to vary with the MRI RF coil used. The copper windings of the RF coils were isolated as the main source of RIC. A linear dependence on dose rate was seen. The RIC was decreased with wax buildup, suggesting an electronic disequilibrium as the cause of RIC. This study shows a measurable RIC present in MRI RF coils. This unwanted current could be possibly detrimental to the signal to noise ratio in MRI and produce image artifacts.

SU‐EE‐A3‐03: Radiation Induced Effects in An 8.5 MHz Magnetic Resonance Imaging Coil

Purpose: Few research groups are involved in integrating magnetic resonance imaging (MRI) with a linear accelerator in order to obtain real‐time MRI images during the treatment beam‐on. Therefore, the radio frequency (RF) coils used in MRI will be irradiated during this real‐time image guided radiotherapy. The radiation effects on RF coils include instantaneous induced currents and long term radiation damage to components. These effects are potential obstacles facing linac‐MRI integration. This work measures and characterizes the instantaneous effect of pulsed radiation on MRI coils. Method and Materials: A CAT Solenoid coil was placed inside an RF cage, to remove RF noise, and connected to a current amplifier. The amplifier output was sent through RF filters to the RF cage exterior and then to an oscilloscope. The cage was placed in the pulsed beam of a linac and the current induced by pulsed radiation was measured by the oscilloscope; the waveforms were then transferred to a PC and power spectral density was calculated. Results: The RF cage was very effective in eliminating the extraneous RF noise from the radiation induced signal. The induced signal is only present when the radiation beam is on and incident upon the coil. The power spectrum of the induced current indicates that most of the power is contained below 1 MHz, but there is signal is present at the coil resonance frequency (8.5 MHz). The induced current a) occurs mainly in the copper winding, b) is reduced if buildup material is placed on the coil and c) increases linearly with the dose rate. Conclusion: Radiation induced current is present in MRI coils, but its impact on imaging is yet to be determined. This, along with magnetic field impact on induced current will be examined using the functioning 0.2 Tesla linac‐MR prototype.

Self-assembly of germanium islands under pulsed irradiation by a low-energy ion beam during heteroepitaxy of Ge/Si(100) structures

The effect of pulsed irradiation by a low-energy (50-250 eV) ion beam with a pulse duration of 0.5 s on the nucleation and growth of three-dimensional germanium islands during molecular-beam heteroepitaxy of Ge/Si(100) structures is investigated experimentally. It is revealed that, at specific values of the integrated ion flux (less than 10 12 cm -2 ), pulsed ion irradiation leads to an increase in the density of islands and a decrease in their mean size and size dispersion as compared to those obtained in the case of heteroepitaxy without ion irra- diation. The observed phenomena are explained in the framework of the proposed model based on the concept of a change in the diffusion mobility of adatoms due to the instantaneous generation of interstitial atoms and vacancies under pulsed ion irradiation. It is assumed that the vacancies and interstitial atoms give rise to an addi- tional surface strain responsible for the change in the binding energy of the adatoms. Under certain conditions, these processes bring about the formation of centers of preferential nucleation of three-dimensional islands at the places where the ions impinge on the surface. The model accounts for the possibility of annihilating vacan- cies and interstitial atoms on the surface of the growing layer. It is demonstrated that the results obtained from the Monte Carlo calculations based on the proposed model are in good agreement with the experimental data.

Laser purification of ultradispersed diamond in aqueous solution

The effect of pulsed radiation from a 2.92-μm, 130-ns Cr3+:Yb3+:Ho3+:YSGG holmium laser and a 510-nm, 20-ns copper vapour laser on an aqueous suspension of ultradispersed diamond is studied. X-ray photoelectron spectroscopy and electron energy loss spectroscopy revealed that exposure of the suspension to holmium laser radiation reduces the concentration of nondiamond carbon impurity in it. This is due to the dissolution of carbon impurity in supercritical aqueous solution, caused by radiation absorption. Dissolution of the nondiamond fraction may serve as an indicator of the solution being in the supercritical state as a result of laser irradiation of liquids. This process can be used for efficient purification of ultradispersed diamonds.

Multiscale modeling of radiation damage: applications to damage production by GeV proton irradiation of Cu and W, and pulsed irradiation effects in Cu and Fe

The damage accumulation in Cu and W is investigated using a multiscale modeling approach. The efficiency for defect production of displacement cascades is calculated using molecular dynamics (MD). The simulation uses the recoil spectra from spallation reactions of 1.1 and 1.9 GeV protons as calculated with the Los Alamos High Energy Transport (LAHET) nuclear transport code. The total number of defects produced under these irradiation conditions is obtained both from the NRT and MD approximations. The value for the change in electrical resistivity produced by the irradiation-induced defect microstructure is compared to experimental values obtained from irradiations with protons of the above energies, showing a better agreement for the lower irradiation energy. The damage evolution is simulated with kinetic Monte Carlo, where the inputs for the calculation are the results from MD previously obtained. A large recovery of the damage is found at room temperature as a result of the migration of interstitial clusters, single vacancies and small vacancy clusters to sinks such as dislocations. Finally the effects of pulsed irradiation have been analyzed in Cu and Fe with similar simulation tools. The results indicate a clear influence of pulsing at 1 Hz, but not at higher frequencies.

Multiscale Modeling of Radiation Damage of Metals and SIC in Inertial Fusion Reactors

The change in SiC properties under neutron irradiation is being experimentally assessed but it is actually far from being well understood. Using Molecular Dynamics (MDCASK-DENIM/LLNL), we show the existence of recombination barriers (metastable defects), and how they affect the cascade analysis. Displacement cascades have been systematically studied and the different role of both sublattices examined. Low-temperature amorphization by damage accumulation has been successfully simulated using MD in accordance with experiments, allowing the understanding (not possible from experiments) of the atomistic sequence of damage. We are also developing new methodologies (tight binding MD) to prove the adequacy of the interatomic potential to describe energetic of configurations needed for diffusion in SiC. The neutron source from target is obtained with time resolution, together with responses after transport in the IFE reactor. The comparison of different primary knock-on atom (PKA) energy spectra from different fusion reactors is given, which is a basic information for displacement cascade analysis. Those spectra are a direct consequence of the neutron spectra in the material (depending on protection). Supported by recent work on atomistic level, the effect of pulsed irradiation was concluded. The time between pulses has a key role in the annealing process of defects. The comparison with average continuous irradiation, and the different behaviour for vacancies and interstitials, are highlighted.

Effect of simultaneous pulsed hyperthermia and pulsed radiation treatment on survival of SiHa cells

Relatively mild temperatures (40–41.5°C) can sensitize human cells to radiation without the development of thermal tolerance to radiosensitization. Therefore there may be a therapeutic benefit to adding mild hyperthermia to brachytherapy regimens for the treatment of cancer. However, the required heating times are long (∼48 h) which renders this approach somewhat impractical. A novel alternative is to combine pulsed brachytherapy with pulsed hyperthermia to enable the total radiation dose to be given at an elevated temperature while the total heating time is kept short. A treatment schedule in which 1 Gy radiation pulses were given once per hour during 5-min heating pulses also delivered once per hour, was investigated in vitro in the human cervical carcinoma line, SiHa. The degree of cytotoxicity and thermoradiosensitization of the cells were assessed by cell survival using the colony forming assay. Cells were exposed to pulsed hyperthermia alone (5 min at 45°C, delivered once per hour), acute hyperthermia alone (45°C), pulsed radiation alone (1 Gy per hour), acute radiation alone, and simultaneous pulsed hyperthermia and pulsed radiation. Pulsed heating alone caused little cytotoxicity. However when pulsed heating was added to pulsed radiation, the level of cytotoxicity was greater than for pulsed radiation alone or acute radiation alone. The effect was also greater than would be predicted from a simple additive effect of pulsed radiation and pulsed heating. In conclusion, pulsed heating at 45°C sensitized cells to pulsed radiation without the development of thermal tolerance.

Effects of pulsed irradiation by low-energy ions during homoepitaxy of silicon from a molecular beam

The change in the morphology of a Si(111) surface under pulsed irradiation by 145-eV Kr+ ions with a pulse duration of 0.5 s during epitaxy of silicon from a molecular beam is studied experimentally by RHEED. It is found that pulsed irradiation by low-energy ions intensifies the specular reflection. This corresponds to a decrease in the roughness of the growing surface. It is shown that the observed effect depends strongly on the degree of filling of the surface atomic layer, the substrate temperature, and the ion current density.

Efficiency of photosynthesis in continuous and pulsed light emitting diode irradiation

The light utilization efficiency and relative photon requirement of photosynthesis in pulsed and continuous light from light emitting diodes (LEDs) has been measured. First, we chacterized the photon requirement of photosynthesis from light of LEDs that differ in spectral quality. A photon requirement of 10.3±0.4 was measured using light from a 658 nm peak wavelength (22 nm half band width) LED over the range of 0-50 μmol photons m(-2) s(-1) in 2 kPa O2 in leaves of tomato (Lycopersicon esculentum Mill., cv. VF36). Because the conversion of electrical power to photons increased with wavelength, LED lamps with peak photon output of 668 nm were most efficient for converting electricity to photosynthetically fixed carbon. The effect of pulsed irradiation on photosynthesis was then measured. When all of the light to make the equivalent of 50 μmol photons m(-2) s(-1) was provided during 1.5 μs pulses of 5000 μmol photons m(-2) s(-1) followed by 148.5 μs dark periods, photosynthesis was the same as in continuous 50 μmol photons m(-2) s(-1). When the pulse light and dark periods were lengthened to 200 μs and 19.8 ms, respectively, photosynthesis was reduced, although the averaged photon flux density was unchanged. Under these conditions, the light pulses delivered 10(17) photons m(-2), which we calculate to be equivalent to the capacitance of PS I or PS II. Data support the theory that photons in pulses of 100 μs or shorter are absorbed and stored in the reaction centers to be used in electron transport during the dark period. When light/dark pulses were lengthened to 2 ms light and 198 ms dark, net photosynthesis was reduced to half of that measured in continuous light. Pigments of the xanthophyll cycle were not affected by any of these pulsed light treatments even though zeaxanthin formation occurred when leaves were forced to dissipate an equal amount of continuous light.

Involvement of Two Different Photoreceptors in the Light Regulation of Glutamine Synthetase Activity in a Chlorophyll-Free Chlorella Mutant

Glutamine synthetase (EC 6.3.1.2) activity of a non-photosynthetic mutant of Chlorella kessleri is markedly enhanced under blue and slightly increased under red light. In both cases, the effect is largest after 6 h of irradiation. In blue light, saturation is reached at about 10 μEm-2 s-1; in red light, it is not even indicated at 62 μE m-2 s-1. Semilogarithmic plots of both intensity dependencies reveal different slopes, indicating envolvement of two separate photoreceptors. This feature is supported by different effects of pulse irradiation: The response to 15 min of red light irradiation (λmax 650 nm) increases in subsequent darkness. It reaches the same value as in continuous light after 6 h. The response to 15 min of blue light irradiation (λmax 441 nm) increases also in subsequent darkness. However, after 6 h it reaches only 30% of the value obtained by continuous irradiation. It is concluded that, glutamine synthetase of Chlorella is controlled by two different photoreceptors both independent of photosynthesis. There is evidence of two forms of glutamine synthetase, the intracellular distribution and specific light regulations of these are discussed.