Irradiation Fluence Research Articles

1 MeV electron irradiation effect and damage mechanism analysis of flexible GaInP/GaAs/InGaAs solar cells

In this study, the degradation behavior of flexible GaInP/GaAs/InGaAs (IMM3J) solar cells and their metamorphic subcells under 1 MeV electron irradiation was investigated. The remaining factors such as short-circuit current density (Jsc), open-circuit voltage (Voc), and maximum power (Pmax) were 95.62, 85.52, and 79.73%, respectively, at an irradiation fluence of 2 × 1015 e/cm2. The spectral responses of the InGaAs and GaAs subcells degraded significantly, and the InGaAs subcell experienced greater degradation than the GaAs subcell after irradiation. In addition, the current-limiting unit was switched from GaInP to InGaAs after irradiation. Defect analysis by deep-level transient spectroscopy (DLTS) revealed that with increasing irradiation fluence, the defects that had the greatest impact on the performance of GaAs subcells were EV + 0.36 and EV + 0.42 eV. For InGaAs subcells, the defects that had the greatest impact on the performance were EV + 0.29 and EV + 0.24 eV. The decrease in the minority carrier lifetime is the main reason for the decrease in the electrical performance of solar cells, and the variation in the effective minority carrier lifetime (τeff) in the subcells with the irradiation fluence was calculated based on the DLTS results. At a fluence of 2 × 1015 e/cm2, the τeff of the GaAs and InGaAs subcells decreased from 2.93 × 10−10 and 9.10 × 10−10 s to 1.56 × 10−11 and 1.60 × 10−12 s, respectively. These results provide a reference for predicting the degradation of short-circuit current and open-circuit voltage of flexible IMM3J.

Comparative study of dose for different fluence of neutron

The comparative study aims to investigate the dose received by materials exposed to different fluence of neutron radiation. The research is significant in the field of nuclear energy and radiation protection, as neutron radiation is one of the most common types of radiation produced by nuclear reactions. In this study, various materials are exposed to different fluence of neutron radiation, and the dose received by each material was measured using dosimeters. The results showed that the dose received by the materials increased with increasing fluence of neutron radiation. Furthermore, the study found that the dose-response relationship different between different materials, highlighting the importance of material selection in radiation protection. The study concludes that a better understanding of the dose-response relationship for different materials can help in the development of more effective radiation shielding materials and improve radiation safety in various applications.

Молекулярно-динамическое исследование механизмов абляции золота под воздействием ультракоротких лазерных импульсов с использованием различных потенциалов

Using simulation with a continuum-atomistic model, a study of ablation under the action of an ultrashort laser pulse on a metal (Au) was carried out. Three regimes of ablation were studied: supercritical expansion, phase explosion, and mechanical spallation. The results for two EAM potentials of gold are compared. A graph of the dependence of the amount of removed substance on the fluence of laser radiation for two potentials is constructed, followed by comparison with experimental data.

Increasing the shelf life of packaged bakery products by their processing of broadband optical radiation of a pulsed xenon lamp

Pulsed xenon lamps generating a wide spectrum of radiation of the megawatt range are sources of a new generation of biocidal radiation, which shows potential in the food industry. The article presents the results of studies of the efficiency of pulsed xenon lamp radiation in relation to antifungal treatment of bakery products in sealed plastic packaging in order to increase their shelf life. The object of research was commercial samples of bakery products packed in polypropylene film. The samples were processed by radiation from a pulsed xenon lamp with power of 300 watts. It is shown that irradiation of bakery products samples in the mode with an integral fluence of broadband optical radiation of 10 J/cm2 and a dose of short-wave UV radiation of 0.6 J/cm2 makes it possible to increase their shelf life several times (on average 2 times for most types of samples) compared with untreated samples. General conclusion: optical radiation of a pulsed xenon lamp has a pronounced antifungal effect and is able to inhibit the development of mold fungi on bakery products, even when they are processed in packaged form. The obtained results can be used in the development of equipment of antifungal treatment of bakery products.

Atomistic modeling of high-speed laser action on thin gold film: determination of main mechnaisms of ablation

The action of an ultrashort laser pulse on a thin gold film was studied using a single-speed nonequilibrium combined continuum-atomistic model, which was further developed in the work. Three ablation modes were studied: supercritical expansion, phase explosion and mechanical spallation. The simulation results are compared with experimental data. The dependence of the amount of removed substance on the fluence of laser radiation was obtained.

Radiation effects of high-fluence reactor neutron on Ni/ β -Ga2O3 Schottky barrier diodes

This study investigates the broad-energy-spectrum reactor-neutron irradiation effects on the electrical characteristics of Ni/β-Ga2O3 Schottky barrier diodes (SBDs), where the irradiated neutron fluence was up to 1 × 1016 cm−2. On the one hand, the high neutron fluence of 1016 cm−2 resulted in a reduction in forward current density by two orders of magnitude and an extremely high on-resistance property due to the radiation-generated considerable series resistance in the SBD. On the other hand, the irradiation brought little influence on the Ni/β-Ga2O3 Schottky contact, since the extracted ideality factor and barrier height from temperature-dependent current–voltage (I–V–T) characteristics showed no significant changes after the radiation. Moreover, the capacitance–voltage (C–V) characterization revealed that the net carrier density in the β-Ga2O3 material was only reduced by 25% at the neutron fluence of 1015 cm−2 but a significant reduction by 2–3 orders at 1016 cm−2. Within the neutron fluence range of 2 × 1014 cm−2 up to 1016 cm−2, the carrier removal rates trended to be saturated with the increased fluences, following an exponential regular. In addition, the C–V measurement on the 1016 cm−2 irradiated sample exhibited an obvious frequency dispersion, and the extracted carrier distribution was not uniform.

Fungal Keratitis: Diagnosis, Management, and Recent Advances.

Fungal keratitis is one of the major causes of microbial keratitis that may lead to corneal blindness. Many problems related to diagnosis and therapy are encountered in fungal keratitis, including difficulty in obtaining laboratory diagnoses and the availability and efficacy of antifungal medications. Intensive and prolonged use of antifungal topical preparations may not be enough. The use of antifungal medications is considered the main treatment for fungal keratitis. It is recommended to start antifungal therapy after confirmation of the clinical diagnosis with a smear or positive cultures. Topical application of antifungal medications is a mainstay for the treatment of fungal keratitis; however, systemic, intra-stromal, or intra-cameral routes may be used. Therapeutic keratoplasty is the main surgical procedure approved for the management of fungal keratitis with good success rate. Intrastromal corneal injection of antifungal medications may result in steady-state drug levels within the corneal tissue and prevent intervals of decreased antifungal drug concentration below its therapeutic level. In cases of severe fungal keratitis with deep stromal infiltration not responding to treatment, intracameral injection of antifungal agents may be effective. Collagen cross-linking has been proposed to be beneficial for cases of fungal keratitis as a stand-alone therapy or as an adjunct to antifungal medications. Although collagen cross-linking has been extensively studied in the past few years, its protocol still needs many modifications to optimize UV fluence levels, irradiation time, and concentration of riboflavin to achieve 100% microbial killing.

Nitrogen-displacement-related recombination centers generated by electron beam irradiation in n-type and p-type homoepitaxial GaN layers

Recombination centers originating from point defects generated by the displacement of N atoms in n-type and p-type GaN were investigated by analyzing Shockley–Read–Hall (SRH) recombination currents in homoepitaxial GaN p–n junctions. These defects were intentionally generated by electron beam (EB) irradiation at 137 keV. The net doping concentrations in p+–n junction diodes were not changed following irradiation although the levels in p–n+ junction diodes decreased as the EB fluence was increased. The SRH recombination current also increased with increases in the fluence. This work additionally evaluated the relationship between recombination lifetimes and trap concentrations obtained by deep level transient spectroscopy.

High conductivity characteristics of phosphorus-doped nanocrystalline silicon thin films by KrF pulsed excimer laser irradiation method.

The microstructure and high conductivity properties of phosphorus-doped nanocrystalline silicon films were investigated on samples prepared by a plasma-enhanced chemical vapor deposition technique and the KrF pulsed excimer laser irradiation method. The results of Fourier transform infrared spectroscopy and Raman spectroscopy show that Si nanocrystallites with an average diameter of 2 nm to 3 nm are formed in the film. The degree of crystallinity increases with the increase of laser radiation intensity, while the content of hydrogen decreases gradually. More phosphorus atoms are substitutionally incorporated into the nc-Si dots under higher laser irradiation fluence, which is responsible for the high dark conductivity. By controlling the laser fluence at 1.0 J cm-2, the dark conductivity as high as 25.7 S cm-1 can be obtained. Based on the measurements of temperature-dependent conductivity, the carrier transport processes are discussed. The phosphorus doping and the increase of electron concentration are considered to be the reason for high dark conductivity and extremely low conductivity activation energy.

Effect of heavy ion radiation on low frequency noise characteristics of AlGaN/GaN high electron mobility transistors

AlGaN/GaN high election mobility transistor (HEMT) has important application prospects in satellite communication, radar, nuclear reactors and other extreme environments, owing to its excellent electrical performance and strong radiation resistance. Heavy ion radiation mainly causes single-event effect and displacement damage effect in AlGaN/GaN HEMT device. In this work, the displacement damage defects introduced by heavy ion radiation are analyzed in detail. With the increase of heavy ion radiation influence, more defects are introduced by displacement damage. These defects reduce the two-dimensional electron gas (2DEG) concentration through carrier capture and removal effect, and reduce the carrier mobility through scattering mechanism, resulting in gradual degradation of the electrical characteristics of the device. In this work, AlGaN/GaN high electron mobility transistors are irradiated by <sup>181</sup>Ta<sup>32+</sup> ions with fluences of 1×10<sup>8</sup> ions/cm<sup>2</sup>, 1×10<sup>9</sup> ions/cm<sup>2</sup> and 1×10<sup>10</sup> ions/cm<sup>2</sup>. The electrical characteristics, EMMI and low-frequency noise characteristics of the device before and after heavy ion radiation are measured. The results show that heavy ion radiation can lead to the degradation of electrical parameters. When the heavy ion radiation dose reaches 1×10<sup>10</sup> ions/cm<sup>2</sup>, the electrical characteristics of the device deteriorate seriously, the threshold voltage shifts forward by 25%, and the drain saturation current deteriorates obviously. The defect locations introduced by irradiation are analyzed by EMMI test, and it is found that the number of “hot spots” increases significantly after the having been irradiated by heavy ions with a fluence of 1×10<sup>10</sup> ions/cm<sup>2</sup>, indicating that the radiation leads to the increase of defect density and serious damage to the device. Through the noise test, it is found that with the increase of the radiation fluence, the current noise power spectral density gradually increases. When the fluence reaches 1×10<sup>10</sup> ions/cm<sup>2</sup>, the defect density increases to 3.19×10<sup>18</sup> cm<sup>–3</sup>·eV<sup>–1</sup>, and the Hooge parameter increases after having been irradiated by heavy ions. We believe that the radiation leads to the defect density and parasitic series resistance of AlGaN/GaN HEMT device to increases, resulting in larger Hooge parameters. Through analyzing the variation of the normalized power spectral density of the drain current noise with bias voltage, it is found that the defects caused by heavy ion radiation will cause the parasitic series resistance to increase.

Simulation of proton-induced primary displacement damage in GaAs under different ambient temperatures

The performance of on-orbit GaAs-based solar cells is susceptible to the displacement damage effect. The proton-induced primary displacement damage in GaAs on a geosynchronous equatorial orbit (GEO) was simulated and analyzed by combining the Monte Carlo (MC) and molecular dynamics (MD) methods. The MC simulation provided the distribution of primary knock-on atoms (PKAs) in GaAs induced by GEO-related protons to the MD simulation. In MD simulations, the effects of radiation fluence and ambient temperature on the displacement damage were considered. The simulation results showed that GEO-related protons generated a significant number of PKAs within an energy range of below 10 keV in GaAs. The high-fluence radiation emulated by the binary PKA could generate more point defects and cluster defects in GaAs than the low-fluence radiation emulated by single PKAs. As compared to room temperature (300 K), both a low (100 K) and high (500 K) ambient temperature could deteriorate the displacement damage. In addition, a high ambient temperature of 500 K could induce widespread thermal spikes in GaAs as compared to 100 and 300 K. This work can provide useful insight into the proton-induced displacement damage in GaAs and the radiation hardening of GaAs-based photoelectric devices in space.

Structural and property engineering of 2D titanium carbides (MXene) thin films using ion irradiation

MXenes are a large family of two-dimensional transition metal carbides and/or nitrides combining hydrophilicity with metallic conductivity, thereby leading to a plethora of potential applications. This study expands the current possibilities for the structural engineering of MXenes by demonstrating medium energy range ion irradiation as a controllable and flexible strategy to deeply modify Ti3C2Tz thin films. By adjusting the fluence of a 180 kV He+ ion beam, we evidence the gradual modification of the different structural elements of typical MXene multilayers, inducing well-defined impacts on properties. Low fluences allow modifying the interlayer spacing, inhibiting the long-term rehydration capacity of the thin films with expected major benefits on MXene aging issues. In addition to this, irradiation allows affecting the layers functionalization with major impact on the normalized optical transmission profile, suppressing the absorption valley at IR-visible limit and expanding their transparency in the UV. These effects, combined with improved electrical contact between the Ti3C2Tz layers, are highly desirable for transparent conductive electrodes applications. Finally, higher fluence irradiations induce preferential sputtering of titanium atoms. Transition metal vacancies being known to be highly relevant to deeply modify properties beyond those investigated here, these results show the large benefits of ion irradiation for MXene design.

Preliminary analysis of the irradiation deformation of a typical molten salt reactor graphite component

Nuclear graphite commonly serves as the moderator and constructs the coolant flowing channel in liquid fuel molten salt reactors. Under irradiation and high temperature, graphite components will experience obvious deformation due to irradiation creep, thermal expansion, dimensional change, elastic deformation, and thermo-mechanical properties change. The lifespan of graphite components is a limiting parameter of liquid fuel molten salt reactors, determining by the deformation of the graphite components. An improved approach based on the finite element method for graphite deformation analysis was proposed in this paper. Then this method was utilized to analyze a 10-year deformation history of a typical graphite component. The findings show that the stress-strain field of the graphite component significantly varies with the increasing irradiated neutron fluence. The dimensional change plays a primary role in influencing the deformation of the graphite components, determining the overall deformation trend. The irradiation creep plays a secondary role in influencing the deformation, alleviating the deformation of the graphite components to prolong the graphite lifespan. The improved method, which considers various factors like irradiation creep, thermal expansion, dimensional change, and elastic deformation, tends to provide more accurate results compared to the traditional method that focuses solely on the dimensional changes. Over 10 years, the contraction deformation of graphite components results in a reduction in graphite volume of up to 3.87%. The space for graphite contraction is filled with molten salt, resulting in a maximum increase of 22.49% in fuel volume. The alteration in volume of both graphite and fuel leads to a reduction in reactivity of up to 840 pcm.

Influence of neutron irradiation on the electronic properties of hexagonal boron nitride measured by terahertz time-domain spectroscopy

Due to the low atomic number of B, hexagonal boron nitride (hBN) has a large neutron scattering cross section and, therefore, is an ideal material for the realization of solid-state neutron detector. Here we apply the THz time-domain spectroscopy to study the effect of neutron irradiation on electronic properties of pyrolytic (PBN) and hot-pressed boron nitride (HBN). The key electronic parameters of these samples, such as the static dielectric constant ε b , the effective carrier density N*, the carrier relaxation time τ, and the electronic localization factor α, are determined optically, and their dependences upon the neutron irradiation fluence (NIF) are examined. We find that for hBN,N* and ε b decrease while τ and |α| increase with increasing NIF. These results can be used to further understand the neutron irradiation effects on the basic physical properties of hBN material. We believe that the results obtained from this work can benefit to the design and application of hBN material for neutron detectors.

Defect analysis of 1-MeV electron irradiated flexible InGaAs solar cells by deep-level transient spectroscopy and photoluminescence

1-MeV electron irradiated InGaAs flexible solar cells were investigated based on solar cell I–V characteristics, external quantum efficiency, photoluminescence, and deep-level transient spectra (DLTS) mesurements. The electrical parameters of the solar cells, including Rs and Rsh, were extracted from the I–V curves. With an increase in irradiation fluence, the electrical and optical characteristics of the solar cells continuously degraded. The Voc, Isc, and Pmax values decreased to 83.16%, 81.96%, and 68.88% of their initial values, respectively, when the irradiation fluence was increased to 2 × 1015 e/cm2. Photoluminescence (PL) emission peak intensity decreased to 0.54% of its original value, and the minority carrier lifetimes derived from fitting PL emission spectra were reduced to 1.25%. DLTS technique was used to analyse the irradiation-induced defect properties. Similar fitting values for the minority carrier lifetimes were obtained from the PL and DLTS measurements.

Surface-Enhanced Raman Scattering Studies of Au-Ag Bimetallic Nanoparticles with a Tunable Surface Plasmon Resonance Wavelength Synthesized by Picosecond Laser Irradiation

Here, we present a simple and green method of preparing Au-Ag bimetallic nanoparticles (NPs) with a tunable surface plasmon resonance (SPR) wavelength by using picosecond laser irradiation. Au-Ag alloy NPs have been produced by irradiating the solutions containing respective metallic salts in a polyvinyl alcohol (PVA) matrix using a picosecond laser in a single-step process. The SPR wavelength of the Au-Ag bimetallic NPs is observed to be shifted/changed with the Au-Ag concentration and the laser irradiation parameters. The Au-Ag NPs embedded in the PVA matrix are advantageous for Surface-Enhanced Raman scattering (SERS) applications. The estimated enhancement factors (EFs) were observed to vary as a function of conditions of the Au-Ag bimetallic alloy NPs synthesis and also on the concentration of Au at a fixed input fluence of irradiation. The SERS active platforms of Au-Ag bimetallic NPs showed EFs as high as of the order of 108 for Crystal Violet (CV) dye samples at nano molar concentrations. The present study demonstrates a simple, single-step, and green method that fabricates Au-Ag alloy-based nanocomposites suitable for SERS investigations with significantly higher orders of EFs.

The effects and mechanisms of 2 MeV proton irradiation on high bias conditions of InP/InGaAs DHBTs

In this work, a 2 MeV proton irradiation experiment has been carried out on self-fabricated InP/InGaAs heterojunction bipolar transistors (HBTs) with fluence of 5 × 1013 H+/cm2 and 1 × 1014 H+/cm2. The degradation and mechanisms have systematically been studied under different bias conditions. The irradiated InP-based HBTs have suffered more sever degradation at low and high bias voltages with larger damage coefficient of current gain (Kβ), due to the increased base recombination current and the slacken collector current respectively. Under high injection current densities, the slow-down of collector current and the collapse of current gain (β) have occurred at increasingly smaller biases as irradiation fluence increases. Consistently, the ideality factor of base current collapses to 1 at high injection current, moreover, the collapse point decreases as fluence increases. The aggravated degradation at high current densities is attributed to the influence of heterojunction barrier effect (HBE) by the structure of the multi-layer collector region. The study would be of great significance for optimizing the device structure and improving the irradiation tolerance.

Study of the Effect of Variation in the Phase Composition of ZrO2/MgO Ceramics on the Resistance to Radiation Damage during Irradiation with Kr15+ Ions

Interest in the modification of zirconium-containing ceramics is rooted in their great prospects for application as materials for creating inert matrices of dispersed nuclear fuel, which can replace traditional fuel containing uranium dioxide, as well as increase the degree of its burnup. Moreover, among the variety of different types of ceramics offered, zirconium dioxide is the most promising, since it has higher thermal conductivity values compared to other types of ceramics, as well as low volumetric thermal expansion. Moreover, the key limitations in the application of these types of ceramics as materials for creating inert matrices are polymorphic transformations, which have a negative impact on changes in the properties of ceramics under external influences. The evaluation results of the impact of change in the ZrO2 ceramics’ phase composition on the radiation damage resistance when subjected to irradiation with heavy ions, comparable in energy to fission fragments, are presented. The objects of study were samples of ZrO2 ceramics doped with MgO, the variation in the concentration of which leads to an acceleration of the processes of polymorphic transformations during thermal sintering, as well as the formation of a ZrO2/MgO-type structure with inclusions in the form of MgO grains. The results of the irradiation effect on the stability of the crystal structure of ceramics to deformation swelling due to the accumulation of deformation inclusions showed that ceramics with a monoclinic structure type are the least stable, for which, in the case of high irradiation fluences, the accumulation of deformation distortions leads to polymorphic transformations of the m—ZrO2 → t—ZrO2 type. During the evaluation of the irradiation effect on the change in mechanical properties and the softening degree, it was found that phase transformations of the m—ZrO2 → t—ZrO2 and t—ZrO2 → c—ZrO2 types lead to an increase in crack resistance by 1.5–2.0 times. Meanwhile, the formation of a structure of the ZrO2/MgO type with inclusions in the form of MgO grains in the interboundary space results in a softening resistance growth by over 7-fold. During tests for determining thermophysical parameters, as well as maintaining stability to crystal structure thermal expansion during prolonged thermal exposure, it was found that phase transformations associated with polymorphic transformations of the t—ZrO2 → c—ZrO2 type led to the preservation of the stability of thermophysical properties, even in the case of high irradiation fluences.

X-Ray Energy Deposition Model for Simulating Asteroid Response to a Nuclear Planetary Defense Mitigation Mission

In the event of a potentially catastrophic asteroid impact, with sufficient warning time, deploying a nuclear device remains a powerful option for planetary defense if a kinetic impactor or other means of deflection proves insufficient. Predicting the effectiveness of a potential nuclear deflection or disruption mission depends on accurate multiphysics simulations of the device's X-ray energy deposition into the asteroid and the resulting material ablation. The relevant physics in these simulations span many orders of magnitude, require a variety of different complex physics packages, and are computationally expensive. Having an efficient and accurate way of modeling this system is necessary for exploring a mission's sensitivity to the asteroid's range of physical properties. To expedite future simulations, we present a completed X-ray energy deposition model developed using the radiation-hydrodynamics code Kull that can be used to initiate a nuclear mitigation mission calculation. The model spans a wide variety of possible mission initial conditions: four different asteroid-like materials at a range of porosities, two different source spectra, and a broad range of radiation fluences, source durations, and angles of incidence. Using blowoff momentum as the primary metric, the model-initiated simulation results match the full radiation-hydrodynamics results to within 10%.

Creation of NV Centers in Diamond under 155 MeV Electron Irradiation

AbstractSingle‐crystal diamond substrates presenting a high concentration of negatively charged nitrogen‐vacancy centers (NV−) are on high demand for the development of optically pumped solid‐state sensors such as magnetometers, thermometers, or electrometers. While nitrogen impurities can be easily incorporated during crystal growth, the creation of vacancies requires further treatment. Electron irradiation and annealing is often chosen in this context, offering advantages with respect to irradiation by heavier particles that negatively affect the crystal lattice structure and consequently the NV− optical and spin properties. A thorough investigation of electron irradiation possibilities is needed to optimize the process and improve the sensitivity of NV‐based sensors. In this work, the effect of electron irradiation is examined in a previously unexplored regime: extremely high energy electrons, at 155 MeV. A simulation model is developed to estimate the concentration of created vacancies and an increase of NV− concentration by more than three orders of magnitude following irradiation of a nitrogen‐rich HPHT diamond over a very large sample volume is experimentally demonstrated, which translates into an important gain in sensitivity. Moreover, the impact of electron irradiation in this peculiar regime on other figures of merits relevant for NV sensing is discussed, including charge state conversion efficiency and spin relaxation time. Finally, the effect of extremely high energy irradiation is compared with the more conventional low energy irradiation process, employing 200 keV electrons from a transmission electron microscope, for different substrates and irradiation fluences, evidencing 60‐fold higher yield of vacancy creation per electron at 155 MeV.