Investigation Of Radiation Damage Research Articles

Molecular dynamics simulations for short-term investigation and kinetic Monte Carlo for long-term investigation of radiation damage in alpha-iron

به کمک شبیه ­سازی دینامیک مولکولی می ­توان تحلیل کوتاه مدت در مقیاس زمانی چند ده پیکوثانیه ­ای را برای مواد آسیب دیده­ی تابشی مورد مطالعه قرار داد. بر همین مبنا به کمک این شبیه ­سازی، تعداد تعادلی عیوب نقطه ­ای بین ­نشین و تهی ­جای و مختصات مکانی آن­ها در آهن- آلفا به دست آورده شد. سپس با استفاده از نتایج حاصل شده، شبیه ­سازی مونت کارلوی جنبشی شیء به منظور بررسی تأثیر بازپخت آهن- آلفای آسیب دیده­ی تابشی انجام شد. نتایج شبیه ­سازی نشان دادند که در بازپخت یکنواخت آهن- آلفای آسیب دیده­ ی تابشی تنها عیوب خوشه ­ای تهی جای بزرگ­تر از 4 تهی جای و >111< تا دماهایی بالاتر از دمای اتاق پایدار باقی می­ مانند.

Point defect formation energies in graphene from diffusion quantum Monte Carlo and density functional theory

Density functional theory (DFT) is widely used to study defects in monolayer graphene with a view to applications ranging from water filtration to electronics to investigation of radiation damage in graphite moderators. To assess the accuracy of DFT in such applications, we report diffusion quantum Monte Carlo (DMC) calculations of the formation energies of some common and important point defects in monolayer graphene: monovacancies, Stone-Wales defects, and silicon substitutions. We find that standard DFT methods underestimate monovacancy formation energies by around 1 eV. The disagreement between DFT and DMC is somewhat smaller for Stone-Wales defects and silicon substitutions. We examine vibrational contributions to the free energies of formation for these defects, finding that vibrational effects are non-negligible. Finally, we compare the DMC atomization energies of monolayer graphene, monolayer silicene, and bulk silicon, finding that bulk silicon is significantly more stable than monolayer silicene by 0.7522(5) eV per atom.

Investigation of radiation damage using thermal spike model for SHI irradiation on Al2O3

The material exposed to energetic radiation may change its properties and performance. Ion beam irradiation is an established method to investigate radiation damage in materials. In the present study, SRIM code is employed as a tool to determine the electronic and nuclear energy losses and displacement per atom (DPA) associated with the damage induced in Al2O3 using 100 MeV Au ion. We have further studied the creation of 100 MeV Au ion induced molten zone along the ion track in Al2O3 in the framework of the thermal spike (TS) model. Using the in-elastic thermal spike model, elastic thermal spike model, and unified thermal spike model, the evolution of lattice temperature and latent track radius as a function of depth of Al2O3 for 100 MeV Au ion irradiation are investigated. The current results demonstrate that the latent track radius shows a U-shaped variation based on the combined effect of electronic stopping power and nuclear stopping power. In order to corroborate these results, an additional irradiation experiment was performed using swift heavy ion (SHI), 100 MeV Au ions with fluence 1×1014 ions/cm2 for Al2O3. To investigate the structural properties, surface morphology and to identify the defects in the samples, pristine and irradiated Al2O3 samples were characterized by Grazing Incident X-Ray Diffraction (GIXRD), Atomic Force Microscopy (AFM) and Photoluminescence Spectroscopy (PL). AFM study shows the increase in roughness after SHI irradiation. A decrease in intensity of PL spectra upon SHI irradiation indicates the formation of new defects and disordered structures in the material, which is quite in agreement with the theoretical results.

Measurement of swelling-induced residual stress in ion implanted SiC, and its effect on micromechanical properties

Ion implantation is widely used as a surrogate for neutron irradiation in the investigation of radiation damage on the properties of materials. Due to the small depth of damage, micromechanical methods must be used to extract material properties. In this work, nanoindentation has been applied to ion irradiated silicon carbide to extract radiation-induced hardening. Residual stress is evaluated using HR-EBSD, AFM swelling measurements, and a novel microcantilever relaxation technique coupled with finite element modelling. Large compressive residual stresses of several GPa are found in the irradiated material, which contribute to the significant hardening observed in nanoindentation measurements. The origin of these residual stresses and the associated hardening is the unirradiated substrate which constrains radiation swelling. Comparisons with other materials susceptible to irradiation swelling show that this effect should not be neglected in studying the effects of ion irradiation damage on mechanical properties. This constraint may also be influencing fundamental radiation defects. This has significant implications for the suitability of ion implantation as a surrogate for neutron irradiations. These results demonstrate the significance of swelling-induced residual stresses in nuclear reactor components, and the impact on structural integrity of reactor components.

Measurement of Swelling-Induced Residual Stress in Ion Implanted Sic, and its Effect on Micromechanical Properties

Ion implantation is widely used as a surrogate for neutron irradiation in the investigation of radiation damage on the properties of materials. Due to the small depth of damage, micromechanical methods must be used to extract material properties. In this work, nanoindentation has been applied to ion irradiated silicon carbide to extract radiation-induced hardening. Residual stress is evaluated using HR-EBSD, AFM swelling measurements, and a novel microcantilever relaxation technique coupled with finite element modelling. Large compressive residual stresses of several GPa are found in the irradiated material, which contribute to the significant hardening observed in nanoindentation measurements. The origin of these residual stresses and the associated hardening is the unirradiated substrate which constrains radiation swelling. Comparisons with other materials susceptible to irradiation swelling show that this effect should not be neglected in studying the effects of ion irradiation damage on mechanical properties. This constraint may also be influencing fundamental radiation defects. This has significant implications for the suitability of ion implantation as a surrogate for neutron irradiations. These results demonstrate the significance of swelling-induced residual stresses in nuclear reactor components, and the impact on structural integrity of reactor components.

Investigation of radiation damage due to particle irradiation on Silicon Drift Detector for Chandrayaan-2 mission

This paper presents the work carrie dout in support of Silicon Drift Detector (SDD) characterization for the Chandrayaan-2 instruments namely Solar X-ray Monitor (XSM) and Alpha Particle X-ray Spectrometer (APXS). The XSM and APXS instruments use SDD to detect X-rays from the Sun and fluorescent X-rays from the lunar surface respectively. The aim of this study is to understand and quantify any spectroscopic performance degradation of these X-ray spectrometers due to space radiation in the SDD during its operational period. Any radiation damage to the SDD leads to increase in the detector leakage current and thus degrades the spectroscopic performance, mainly the energy resolution. The expected end-of-life (EOL) 10 MeV equivalent proton fluence was modeled using SPENVIS simulation software. The Silicon Drift Detector was irradiated with 10 MeV protons for the doses up to 24 krad in logarithmic steps and measured the energy resolution and the leakage current at each dose. The spectrometer energy resolution degraded from ∼ 142 eV at 5.9 keV to ∼ 250 eV for the cumulative proton dose of ∼ 11 krad for the mission life of one year. This satisfies the performance requirement of the SDD based X-ray spectrometers onboard Chandrayaan-2 mission.

Exploitation of thermal gradients for investigation of irradiation temperature effects with charged particles

The effects of radiation damage on materials are strongly dependant on temperature, making it arguably the most significant parameter of concern in nuclear engineering. Owing to the challenges and expense of irradiating and testing materials, material property data is often limited to few irradiation conditions and material variants. A new technique has been developed which enables the investigation of radiation damage of samples subject to a thermal gradient, whereby a wealth of data over a range of irradiation temperatures is produced from a single irradiation experiment. The results produced are practically inaccessible by use of multiple conventional isothermal irradiations. We present a precipitation-hardened copper alloy (CuCrZr) case-study irradiated with a linear temperature gradient between 125 and 440 °C. Subsequent micro-scale post irradiation characterisation (nanoindentation, transmission electron microscopy and atom probe tomography) highlight the capability to observe mechanical and microstructural changes over a wide range of irradiation temperatures. We observed irradiation-softening in CuCrZr that did not occur due to irradiation-enhanced aging of the Cr-precipitates. Excellent reproducibility of the new technique was demonstrated and replicated irradiation-hardening data from several isothermal neutron irradiation studies. Our new technique provides this data at a fraction of the time and cost required by conventional irradiation experiments.

Radiation-damage investigation of a DNA 16-mer.

In macromolecular crystallography, a great deal of effort has been invested in understanding radiation-damage progression. While the sensitivity of protein crystals has been well characterized, crystals of DNA and of DNA-protein complexes have not thus far been studied as thoroughly. Here, a systematic investigation of radiation damage to a crystal of a DNA 16-mer diffracting to 1.8 Å resolution and held at 100 K, up to an absorbed dose of 45 MGy, is reported. The RIDL (Radiation-Induced Density Loss) automated computational tool was used for electron-density analysis. Both the global and specific damage to the DNA crystal as a function of dose were monitored, following careful calibration of the X-ray flux and beam profile. The DNA crystal was found to be fairly radiation insensitive to both global and specific damage, with half of the initial diffraction intensity being lost at an absorbed average diffraction-weighted dose, D1/2, of 19 MGy, compared with 9 MGy for chicken egg-white lysozyme crystals under the same beam conditions but at the higher resolution of 1.4 Å. The coefficient of sensitivity of the DNA crystal was 0.014 Å2 MGy-1, which is similar to that observed for proteins. These results imply that the significantly greater radiation hardness of DNA and RNA compared with protein observed in a DNA-protein complex and an RNA-protein complex could be due to scavenging action by the protein, thereby protecting the DNA and RNA in these studies. In terms of specific damage, the regions of DNA that were found to be sensitive were those associated with some of the bound calcium ions sequestered from the crystallization buffer. In contrast, moieties farther from these sites showed only small changes even at higher doses.

New Microscope and Ion Accelerators for Materials Investigations (MIAMI-2) system at the University of Huddersfield

Radiation damage is a complex dynamic process with multiple atomic mechanisms interacting and competing to determine the end state of the material. Transmission electron microscopy (TEM) with in-situ ion irradiation allows direct observation of the microstructural evolution of a sample from the virgin to end state. A new TEM with in-situ ion irradiation has been established at the University of Huddersfield: the Microscope and Ion Accelerators for Materials Investigations (MIAMI-2) system. MIAMI-2 combines a 300 kV TEM with medium-energy 350 kV and low-energy 20 kV ion beamlines. Whilst the medium-energy beamline can be used for most species up to Au, the low-energy beamline is primarily designed for implanting light-ion species such as H and He. These can be used individually or mixed prior to entering the TEM allowing dual-ion-beam irradiation experiments to, for example, simulate the combined effects of displacement damage and the introduction of He from (n, α ) nuclear reactions. The TEM can operate from 60–300 kV and is equipped with a 16 megapixel digital camera, an energy-filtered imaging system and an energy-dispersive X-ray spectrometer for elemental and chemical analysis. Sample temperature can be varied from –170 °C to 1300 °C and a gas injection system enables gaseous environments at pressures of up to 10 − 2 mbar at the sample position. The new MIAMI-2 system is a powerful tool for the investigation of radiation damage in a wide range of materials which are exposed to irradiating environments either during processing and/or whilst in-service in areas including nuclear applications, nanotechnology, semiconductor processing and extraterrestrial environments.

An investigation of radiation damage in rat lungs following dual-energy micro-CT imaging

Dual-energy micro-CT imaging techniques have been developed to enable accurate identification and segmentation of different tissues. Using dual-energy techniques for thoracic imaging requires obtaining images at multiple respiratory or cardiac phases, and may require images obtained pre- and post-contrast enhancement for each energy. In this study, we investigated if the multiple images obtained during dual-energy imaging resulted in an x-ray dose sufficiently high to interfere with or mask symptoms of respiratory disease. We performed a dual-energy micro-CT study (5 images in a single session, with a cumulative entrance dose of 0.47 Gy) to image the thorax of healthy male Brown Norway rats at 8 weeks of age. Groups of 5 rats were euthanized at 1 day, 1, 2, 3, and 4-weeks post-exposure and the lungs were excised and examined by histology (H&E stained slides). Positive controls were exposed to an entrance dose of 1.5 Gy and euthanized at 2 weeks and negative controls were not exposed to x-rays. There was no evidence of alveolar damage or inflammation for any of the animals exposed to the dual-energy imaging session compared with the negative control group. Inflammation was evident for the positive controls. This study concludes that the dual-energy imaging protocol developed in this study does not contribute to lung tissue damage. For preclinical respiratory research, these results show that any inflammation and alveolar damage observed in the lungs would be attributed to the disease model under investigation, and not be affected by obtaining 3D dual-energy micro-CT images.

Cross-sectional investigation of radiation damage of 2 MeV proton-irradiated silicon carbide

Cross-sectional investigation is an important method to study ion irradiation effects in the depth direction. In this study, 2 MeV H+ was implanted in 6H-SiC single crystals to investigate the effects of light ion irradiation on SiC. Raman spectroscopy and scanning electronic microscopy (SEM) were carried out on cross-sectional samples to reveal the in-depth damage states and dopant behavior. The most damaged region is a little shallower than that predicted by the SRIM procedure, owing to the uncertainty in SRIM simulations. Layered structures representing zones of varying damage after 2 MeV H ion irradiation are clearly observed. Two bands are observed in SEM images, of which on band corresponds to the damage peak, while the other band at the end of the H ion-affected area is probably a result of H diffusion propelled by a hydrogen-rich layer during irradiation. A charge accumulation effect related with conductivity on the sample surfaces during SEM tests is observed in the H-implanted area. A model is proposed to explain these phenomena.

Computational mechanistic investigation of radiation damage of adenine induced by hydroxyl radicals**Project supported by the National Natural Science Foundation of China (Grant Nos. 11564015 and 61404062), the Research Fund for the Doctoral Program of China (Grant No. 3000990110), and the Fund for Distinguished Young Scholars of Jiangxi Science & Technology Normal University (Grant Nos. 2015QNBJRC002 and 2016QNBJRC006).

The radiation damage of adenine base was studied by B3LYP and MP2 methods in the presence of hydroxyl radicals to probe the reactivities of five possible sites of an isolated adenine molecule. Both methods predict that the C8 site is the more vulnerable than the other sites. For its bonding covalently with the hydroxyl radicals, B3LYP predicts a barrierless pathway, while MP2 finds a transition state with an energy of 106.1 kJ/mol. For the hydroxylation at the C2 site, the barrier was calculated to be 165.3 kJ/mol using MP2 method. For the dehydrogenation reactions at five sites of adenine, B3LYP method predicts that the free energy barrier decreases in the order of H8 > H2 > HN62 > HN61 > HN9.

Radiation hardness of dsipm sensors in a proton therapy radiation environment

In vivo verification of dose delivery in proton therapy by means of positron emission tomography (PET) or prompt gamma imaging is mostly based on fast scintillation detectors. The digital silicon photomultiplier (dSiPM) allows excellent scintillation detector timing properties and is thus being considered for such verification methods. We present here the results of the first investigation of radiation damage to dSiPM sensors in a proton therapy radiation environment. Radiation hardness experiments were performed at the AGOR cyclotron facility at the KVI-Center for Advanced Radiation Technology, University of Groningen. A 150-MeV proton beam was fully stopped in a water target. In the first experiment, bare dSiPM sensors were placed at 25 cm from the Bragg peak, perpendicular to the beam direction, a geometry typical for an in situ implementation of a PET or prompt gamma imaging device. In the second experiment, dSiPM-based PET detectors containing lutetium yttrium orthosilicate scintillator crystal arrays were placed at 2 and 4 m from the Bragg peak, perpendicular to the beam direction; resembling an in-room PET implementation. Furthermore, the experimental setup was simulated with a Geant4-based Monte Carlo code in order to determine the angular and energy distributions of the neutrons and to determine the 1-MeV equivalent neutron fluences delivered to the dSiPM sensors. A noticeable increase in dark count rate (DCR) after an irradiation with about 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> 1-MeV equivalent neutrons/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> agrees with observations by others for analog SiPMs, indicating that the radiation damage occurs in the single photon avalanche diodes and not in the electronics integrated on the sensor chip. It was found that in the in situ location, the DCR becomes too large for successful operation after the equivalent of a few weeks of use in a proton therapy treatment room (about 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> protons). For PET detectors in an in-room setup, detector performance was unchanged even after an irradiation equivalent to three years of use in a treatment room (3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> protons).

Final design, fluid dynamic and structural mechanical analysis of a liquid hydrogen Moderator for the European Spallation Source

The European Spallation Source (ESS) is currently in the construction phase and should have first beam on Target in 2019. ESS, located in Sweden, will be the most powerful spallation neutron source worldwide, with the goal to produce neutrons for research. As an in-kind partner the Forschungszentrum Juelich will among others, design and manufacture the four liquid hydrogen Moderators, which are located above and below the Target. Those vessels are confining the cold hydrogen used to reduce the energy level of the fast neutrons, produced by spallation in the Target, in order to make the neutrons usable for neutron scattering instruments. Due to the requirements [1], a fluid dynamic analysis with pressure and temperature depended hydrogen data, taking into account the pseudo critical phenomena and the pulsed neutronic heating (pressure waves) is necessary. With the fluid dynamic results, a structure mechanical analysis including radiation damage investigation (RCC-MRx code [5]), low temperature properties as well as strength reduction by welding can be realized. Finally, the manufacturing and welding completes the design process.

Separation of radiation defects in Ni and Ni-C alloys under electron and neutron irradiation

Complex investigations of radiation damage of Ni and Ni- 880 at. ppm C alloy under electron and neutron irradiation in the region of room temperature hardened and deformed state. In pure nickel, with the deformation microstructure, both in electron and in the neutron irradiation is observed separation of radiation-induced defects. When electron irradiation in the alloy Ni-C separation effect is observed, and when neutron irradiation there is no. This is due to the interaction of carbon atoms with radiation defects. The main sinks for radiation-induced defects are the areas with a high concentration of defects in cascades of atomic displacements.

Spectroscopic properties and radiation damage investigation of a diamond based Schottky diode for ion-beam therapy microdosimetry

In this work, a detailed analysis of the properties of a novel microdosimeter based on a synthetic single crystal diamond is reported. Focused ion microbeams were used to investigate the device spectropscopic properties as well as the induced radiation damage effects. A diamond based Schottky diode was fabricated by chemical vapor deposition with a very thin detecting region, about 400 nm thick (approximately 1.4 μm water equivalent thickness), corresponding to the typical size in microdosimetric measurements. A 200 × 200 μm2 square metallic contact was patterned on the diamond surface by standard photolithography to define the sensitive area. Experimental measurements were carried out at the Ruder Boškovic′ Institute microbeam facility using 4 MeV carbon and 5 MeV silicon ions. Ion beam induced charge maps were employed to characterize the microdosimeter response in terms of its charge collection properties. A stable response with no evidence of polarization or memory effects was observed up to the maximum investigated ion beam flux of about 1.7 × 109 ions·cm−2·s−1. A homogeneity of the response about 6% was found over the sensitive region with a well-defined confinement of the response within the active area. Tests of the radiation damage effect were performed by selectively irradiating small areas of the device with different ion fluences, up to about 1012 ions/cm2. An exponential decrease of the charge collection efficiency was observed with a characteristic decay constant of about 4.8 MGy and 1 MGy for C and Si ions, respectively. The experimental data were analyzed by means of GEANT4 Monte Carlo simulations. A direct correlation between the diamond damaging effect and the Non Ionizing Energy Loss (NIEL) fraction was found. In particular, an exponential decay of the charge collection efficiency with an exponential decay as a function of NIEL is observed, with a characteristic constant of about 9.3 kGy-NIEL for both carbon and silicon ions.

Insight into the Mechanism of the Initial Reaction of an OH Radical with DNA/RNA Nucleobases: A Computational Investigation of Radiation Damage.

Earlier theoretical investigations of the mechanism of radiation damage to DNA/RNA nucleobases have claimed OH radical addition as the dominating pathway based solely on energetics. In this study we supplement calculations of energies with the kinetics of all possible reactions with the OH radical through hydrogen abstraction and OH radical addition onto carbon sites, using DFT at the ωB97X-D/6-311++G(2df,2pd) level with the Eckart tunneling correction. The overall rate constants for the reaction with adenine, guanine, thymine, and uracil are found to be 2.17×10(-12) , 5.64×10(-11) , 2.01×10(-11) , and 5.03×10(-12) cm(3) molecules(-1) s(-1) , respectively, which agree exceptionally well with experimental values. We conclude that abstraction of the amine group hydrogen atoms competes with addition onto C8 as the most important reaction pathway for the purine nucleobases, while for the pyrimidine nucleobases addition onto C5 and C6 competes with the abstraction of H1 . Thymine shows favourability against abstraction of methyl hydrogens as the dominating pathway based on rate constants. These mechanistic conclusions are partly explained by an analysis of the electrostatic potential together with HOMO and LUMO orbitals of the nucleobases.

Radiation Damage Investigation on Certain Alternative Fluids in a Hybrid System by Using MCNPX Monte Carlo Radiation Transport Code

Radiation Damage Investigation on Certain Alternative Fluids in a Hybrid System by Using MCNPX Monte Carlo Radiation Transport Code

Femtosecond X-ray-induced fragmentation of fullerenes

A new class of femtosecond, intense, short – wavelength lasers – the free-electron laser – has opened up new opportunities to investigate the structure and dynamics in many scientific areas. These new lasers, whose performance keeps increasing, enable the understanding of physical and chemical changes at an atomic spatial scale and on the time scale of atomic motion which is essential for a broad range of scientific fields. We describe here the interaction of fullerenes in the multiphoton regime with the Linac Coherent Light Source (LCLS) X-ray free-electron laser at SLAC National Laboratory. In particular, we report on new data regarding the ionization of Ho3N@C80 molecules and compare the results with our prior C60 investigation of radiation damage induced by the LCLS pulses. We also discuss briefly the potential impact of newly available instrumentation to physical and chemical sciences when they are coupled with FELs as well as theoretical calculations and modeling.

Silicon Photomultiplier characterization and radiation damage investigation for high energy particle physics applications

Within the framework of the CALICE collaboration, our group has characterized Silicon Photomultipliers (SiPMs) from various producers, in order to enhance the single cell performances of a highly granular analog hadron calorimeter, with particular emphasis on improving the linearity of the response, ensuring environmental stability, calibration portability and reducing the parameters spread among the different channels. As an outcome, new plastic scintillator tiles coupled to KETEK PM1125 SMD SiPM have been commissioned, characterized and mounted on calorimeter modules: details and results of the characterization procedure, together with the performances of the new tile and SiPM design will be discussed. The radiation tolerance to X-rays of KETEK PM1125 is also under investigation. The amount and type of damage caused by irradiation of the devices exposed to 3 kGy and 20 MGy doses will be presented.