Level Of Radiation Damage Research Articles

Study of Radiation Defects in metal Mo and Ta by Mössbauer effect and EXAFS

The implantation of 57Fe atoms into refractory metals Mo and Ta was studied by X-ray diffraction, Mössbauer spectroscopy, and EXAFS. When irradiated with 57Fe ions with energy of 1 MeV and fluence of 5 × 1016 ions/cm2, Fe implantation occurred to a depth of about 600 nm, while creating an extremely strong level of radiation damage with DPA ≥100. Experimental data have confirmed the preservation of the original bcc crystal structure. The localization of 57Fe atoms in the Mo and Ta was studied by Mössbauer spectroscopy and by the EXAFS method in the Fe K-edge region. Both methods give consistent results. In Mo, Fe atoms are predominantly localized in substitutional positions with 1.4 atomic vacancies localized in the first coordinate sphere. Fe atoms in the Ta matrix have a more complex localization. The model spectra for typical atomic configurations of Fe in the Ta were calculated by the density functional theory. Comparison of the experimental spectra with the calculated ones showed that Fe atoms are localized in Ta in several positions, including interstitial and substitutional positions. It is shown that the EXAFS method more accurately determines the configurations of defects caused by irradiation.

Proton irradiation effects in Molybdenum-Carbide-Graphite composites

The High Luminosity upgrade of the Large Hadron Collider (HL-LHC) has prompted the investigation of novel materials for beam-intercepting devices, and in particular for the collimators responsible for protecting the machine from beam losses. The HL-LHC collimation system will inevitably experience increased levels of radiation damage and undergo changes in their crucial physio-mechanical properties. Graphite-matrix composite materials containing molybdenum carbide particles, along with small amounts of titanium carbide, were developed with the objective of enhanced in-beam performance and tested under proton irradiation. The physical degradation observed in early grades of molybdenum carbide compounds, even after modest proton fluences, has prompted the development of advanced compounds. In this work, we examine the effects of proton irradiation on the microstructural and thermophysical properties of new grades of Molybdenum-carbide-graphite compounds up to fluences of ~2 × 10 20 p/cm 2 . We employ a combination of precision dilatometry and high-energy X-ray diffraction to quantify the dimensional stability and crystallographic phase evolution both pre- and post-irradiation. Our results reveal that these new compounds exhibit superior resilience to radiation damage than their predecessors.

Impact of plasma-wall interaction and exhaust on the EU-DEMO design

Abstract In the present work, the role of plasma facing components protection in driving the EU-DEMO design will be reviewed, focusing on steady-state and, especially, on transients. This work encompasses both the first wall (FW) as well as the divertor. In fact, while the ITER divertor heat removal technology has been adopted, the ITER FW concept has been shown in the past years to be inadequate for EU-DEMO. This is due to the higher foreseen irradiation damage level, which requires structural materials (like Eurofer) able to withstand more than 5 dpa of neutron damage. This solution, however, limits the tolerable steady-state heat flux to ~1 MW/m2, i.e. a factor 3–4 below the ITER specifications. For this reason, poloidally and toroidally discontinuous protection limiters are implemented in EU-DEMO. Their role consists in reducing the heat load on the FW due to charged particles, during steady state and, more importantly, during planned and off-normal plasma transients. Concerning the divertor configuration, EU-DEMO currently assumes an ITER-like, lower single null (LSN) divertor, with seeded impurities for the dissipation of the power. However, this concept has been shown by numerous simulations in the past years to be marginal during steady-state (where a detached divertor is necessary to maintain the heat flux below the technological limit and to avoid excessive erosion) and unable to withstand some relevant transients, such as large ELMs and accidental loss of detachment. Various concepts, deviating from the ITER design, are currently under investigation to mitigate such risks, for example in-vessel coils for strike point sweeping in case of reattachment, as well as alternative divertor configurations. Finally, a broader discussion on the impact of divertor protection on the overall machine design is presented.

Use of combined linear and nonlinear ultrasound to examine microstructural and microchemical variations in highly irradiated 304 stainless steel

This research combines linear and nonlinear ultrasound to examine the microstructural and microchemical changes in five large, highly irradiated cold-worked ANSI 304 stainless steel coin specimens cut from two hexagonal cross section blocks with radiation damage levels ranging from ~0.4 to ~33 dpa following irradiation in the EBR-II fast reactor. Both linear (velocity) and nonlinear ultrasonic (β) measurements were conducted in a hot cell using an automated fixture device specially designed to hold the sensor for repeatable measurements in an environment where direct human access is limited, demonstrating their potential to more fully investigate the complex defect ensemble introduced by irradiation. The measurements were performed at the Westinghouse Churchill site hot cell facility.The linear measurements agree very well with previous measurements employing a different sensor application technique. The ultrasonic nonlinearity parameters measured after irradiation increased by more than 100% from the unirradiated state and show a level of random variation below 4.7%. These ultrasonic nonlinearity parameters also show a spatial dependence on measurement location across each of the specimens in agreement with the spatial inhomogeneity of microstructure and microchemical distribution previously observed in adjacent, nominally identical specimens using transmission electron microscopy (TEM) and atom probe tomography (APT). It is proposed that the inhomogeneous distribution of microstructural and microchemical features including Frank loops, and both intragranular and grain boundary precipitates, as well as their different nonlinearity generation efficiencies are responsible for the spatial dependence of the measured ultrasonic nonlinearity parameters. The major and dominant component of the microstructure of these specimens at 20–30 dpa is vacancy agglomerations called voids, previously observed by microscopy and measurable using either linear ultrasonic velocity or linear attenuation, but which are not readily visible using nonlinear ultrasound. Components such as Frank loops, which are one of the other major microstructural components, do not contribute significantly to changing the linear ultrasonic velocity. Using this combination of linear and nonlinear measurements allows for the examination of microstructural/microchemical components whose linear ultrasonic interactions are overshadowed by voids, especially Frank loops and various radiation-induced precipitates.The changes in ultrasonic nonlinearity parameters in these specimens are thought to arise from two major sources. The smaller contribution is due to carbide pinning of dislocations in the grain boundary walls and the few line dislocations present in the grain interior. The largest contribution appears to come from segregation of Ni and Si to the perimeter of the very high density of Frank loops, leading to the formation of Ni3Si precipitates which are thought to be very efficient at pinning the Frank loops. These results on two hex blocks provide an ideal, though not completely realistic, test case to demonstrate the sensitivity of nonlinear ultrasound to two different microstructure sources.

Tensile behavior of dual-phase titanium alloys under high-intensity proton beam exposure: Radiation-induced omega phase transformation in Ti-6Al-4V

A high-intensity proton beam exposure with 181 MeV energy has been conducted at Brookhaven Linac Isotope Producer facility on various material specimens for accelerator targetry applications, including titanium alloys as a beam window material. The radiation damage level of the analyzed capsule was 0.25 dpa at beam center region with an irradiation temperature around 120 °C. Tensile tests showed increased hardness and a large decrease in ductility for the dual α+β-phase Ti-6Al-4V Grade-5 and Grade-23 extra low interstitial alloys, with the near α-phase Ti-3Al-2.5V Grade-9 alloy still exhibiting uniform elongation of a few % after irradiation. Transmission Electron Microscope analyses on Ti-6Al-4V indicated clear evidence of a high-density of defect clusters with size less than 2 nm in each α-phase grain. The β-phase grains did not contain any visible defects such as loops or black dots, while the diffraction patterns clearly indicated ω-phase precipitation in an advanced formation stage. The radiation-induced ω-phase transformation in the β-phase could lead to greater loss of ductility in Ti-6Al-4V alloys in comparison with Ti-3Al-2.5V alloy with less β-phase.

Fretting wear behaviors of Zr-4 alloy under different ions irradiation conditions

Studying the fretting wear behaviors of Zr-4 alloy under various ions irradiation conditions plays an important role in understanding the fretting damage source of cladding in nuclear reactor. In the study, fretting wear behaviors for Zr-4 alloy under various ions irradiation conditions were summarized as function of irradiation damage level, incident ion energy and ion species. The results demonstrate that increasing incident energy produced partially or completely amorphous phase in Zr-4 alloy. The friction coefficient and wear rate increase linearly with the increase of irradiation dose, but both are saturated at high irradiation dose, which can be attributed to the existence of an adiabatic or instantaneous recombination volume around the defect. Heavy ions irradiation with large mass and radius cause more and denser defects at shallower surface than ions with smaller radius, results in lower friction coefficient but increased the wear depth and wear rate. Conclusively, the friction coefficient and wear rate of Zr-4 alloy increase at the irradiation conditions investigated in this study. The dominant wear mechanism changes from adhesive wear and abrasive wear to fatigue wear and abrasive wear.

Effectiveness of Photoprotective Strategies in Three Mixotrophic Planktonic Ciliate Species

Mixotrophic ciliate assemblages often prevail in summer in the surface layers of lakes. During this time, they are potentially exposed to damaging levels of incident solar ultraviolet radiation (UVR) and need efficient photoprotective mechanisms to minimize the damage. Herein, we tested the algal-bearing species of Pelagodileptus trachelioides, Stokesia vernalis, and Vorticella chlorellata for how they handled stress under exposure to the artificial sunlight spectrum (i.e., UV treatment), just photosynthetically active radiation (PAR), or in the dark (i.e., control). In addition to measurements of their survival, changes in behavior, shape, and whether dark or photoenzymatic repair (PER) mechanisms are present, we measured the concentration of UV-absorbing compounds (i.e., mycosporine-like amino acids). In contrast to the response in the PAR and dark treatments, sublethal effects were observed in all species when exposed to UVR. A wavelength-specific test for P. trachelioides revealed that UV-B was especially lethal. These results suggest that the photoprotective mechanisms found in these ciliates are not sufficient to allow for their survival directly at the surface and that, accordingly, they need to shift their position further down in the water column.

TCAD silicon device simulation for high level of radiation damage

Silicon detectors are expected to experience an unprecedented radiation flux in the future upgrades of the detectors at the Large Hadron Collider (LHC). The challenging radiation environment of these experiments will severely affect the performance of such detectors, degrading their detection capabilities and imposing severe operational conditions. The modeling of the detectors through Monte Carlo simulation represents a necessary step for the detailed understanding of the silicon detector performance before and after radiation damage; also for setting up optimized design rules aiming to mitigate the detrimental effect of the radiation damage. In the present work, a comparison of simulation results, obtained from- Technology Computer-Aided Design (TCAD) simulation software: Silvaco and Synopsys- used to predict silicon detectors performance, is presented. The effects of radiation damage are incorporated in the TCADs, using an effective multiple traps model. A systematic study of the sensitivity of the silicon detector's macroscopic parameters to the modeling of traps is performed. The simulation results for static electrical parameters, such as the leakage current and the full depletion voltage, obtained by the TCADs are presented and compared.

Influence of ion irradiation on the nanomechanical properties of thin alumina coatings deposited on 316L SS by PLD

In terms of nuclear applications, ceramics are seen as a particularly promising class of materials due to their chemical inertness and relatively high radiation resistance. However, since ceramics exhibit high brittleness at low homologous temperatures, the application of monolithic ceramics as structural components of nuclear power plants is rather limited. On the other hand, deposition of ceramic coatings on a metallic substrate may result in an excellent combination of mechanical, corrosion and radiation properties (especially at high temperature). In this work, Al2O3 coatings deposited by Pulsed Laser Deposition (PLD) on 316L SS substrate at room temperature were investigated. In order to simulate the influence of neutrons, alumina-coated and 316L SS samples were irradiated at room temperature with 250 keV Au+ and 150 keV Fe2+ ions, respectively. The influence of ion irradiation on nanomechanical properties of the studied materials was investigated by means of Nanoindentation (NI) technique. Based on the obtained results, nanomechanical properties as a function of radiation damage level were determined and linked to the results of Grazing Incidence X-Ray Diffraction (GIXRD) analysis and other structural data available in the literature. Irradiation-induced softening and hardening were observed, respectively, in the alumina coating and 316L SS. Reported differences, which are induced by the irradiation effects, are considered to be due to the different microstructures of the pristine materials.

Wear behavior of zirconium-4 alloy after different irradiation damage level

Effect of neutron irradiation damage on fretting wear of Zirconium-4 alloy was simulated using ions irradiation in previous work, but the evolution of structure and tribological properties as a function of irradiation fluence is not considered. Therefore, in this study, 3 MeV Fe11+ ions were used with the irradiation fluence from 4.31 × 1013 to 4.31 × 1015 cm−2, corresponding to the damage level from 0.1 to 10 dpa. The results show that fine grains, higher density of dislocations, point defects as well as disorder area were observed in damage zone. The increased grain boundaries caused by small grain together with the irradiation-induced defects served as the obstacles of dislocations, leading to the higher hardness. The friction coefficient increases from original 0.6 to 1.2 after damage level to 0.5 dpa and turn to saturation with further increasing the damage to 10 dpa. Obvious wear aggravation as similar change tendency as the friction coefficient after 0.5 dpa damage level was also observed. These changes in wear behaviors of Zirconium-4 alloy after irradiation can be attributed to the additional energy dissipation caused by surface fracture, the sharper wear debris and the increase of friction force resulted from the obstruction of dislocation movement in the irradiated sample.

An Incremental Model for Defect Production upon Cascade Overlapping**Supported by the National Key Research and Development Program of China (No. 2017YFB0702201) and the National Natural Science Foundation of China (No. 51571129).

An analytic incremental model is proposed to predict the defect production upon cascade overlapping. By resolving the coupled annealing events during cascade overlapping, this model handles cascade overlapping with multiple pre-existing defects of different sizes and number densities. The model is first parameterized and then applied to bcc-Fe. The proposed model satisfyingly reproduces the defect production obtained by molecular dynamics simulations with various radiation damage levels and defect cluster size distributions. The present model provides an essential description of the primary source of radiation damage, especially for high dose irradiation, and could be used in conjunction with reactive diffusion models for better understanding of radiation damage.

Features of the 1640 cm−1 band in the Raman spectra of radiation-damaged and nano-sized diamonds

Raman spectra of irradiated with fast neutrons or MeV ion-implanted radiation-damaged natural and CVD diamonds and chemically purified detonation nanodiamonds are investigated. The influence of radiation damage level and effects of high-temperature annealing on the intensity and spectral shape of the 1640 cm−1 band is studied. It is shown that in radiation-damaged diamonds this band consists of at least six Gaussian peaks, the intensity of which varies one to one both with the level of radiation disordering and the temperature of the subsequent annealing. The “1640” band in radiation-damaged diamonds is completely annealed at temperatures above 1000 °C, while in detonation nanodiamonds annealing up to 1200 °C does not significantly affect its shape and intensity.

Bayesian machine learning improves single-wavelength anomalous diffraction phasing.

Single-wavelength X-ray anomalous diffraction (SAD) is a frequently employed technique to solve the phase problem in X-ray crystallography. The precision and accuracy of recovered anomalous differences are crucial for determining the correct phases. Continuous rotation (CR) and inverse-beam geometry (IBG) anomalous data collection methods have been performed on tetragonal lysozyme and monoclinic survivin crystals and analysis carried out of how correlated the pairs of Friedel's reflections are after scaling. A multivariate Bayesian model for estimating anomalous differences was tested, which takes into account the correlation between pairs of intensity observations and incorporates the a priori knowledge about the positivity of intensity. The CR and IBG data collection methods resulted in positive correlation between I(+) and I(-) observations, indicating that the anomalous difference dominates between these observations, rather than different levels of radiation damage. An alternative pairing method based on near simultaneously observed Bijvoet's pairs displayed lower correlation and it was unsuccessful for recovering useful anomalous differences when using the multivariate Bayesian model. In contrast, multivariate Bayesian treatment of Friedel's pairs improved the initial phasing of the two tested crystal systems and the two data collection methods.

Comparison of dose statistics for bladder wall and rectum wall vs whole organs for VMAT prostate treatment

Dose-wall histograms (DWHs) have been used as alternatives to dose-volume histograms (DVHs) for hollow organs, with the rationale that the dose delivered to the interior of a hollow organ would be unrelated to the level of radiation damage. The purpose of this study is to conduct a statistical comparison of dose statistics for both walled and solid structure contours for both bladder and rectum in the treatment of intermediate risk prostate cancer with volumetric arc therapy (VMAT). Ten intermediate risk prostate cases were randomly selected. Rectum and bladder were first contoured as solid structures, and then the corresponding wall structures were generated using either a slice-by-slice cropping (2D method), or with a full 3D cropping tool (3D method). Each case was then inverse planned using a 2-arc VMAT technique. Two plans per case were created, 1 with a hypofractionated treatment and 1 with a standard fractionated treatment. DVHs were calculated for solid structure contours, and DWHs were calculated for the walled structure contours generated using 2D and 3D contouring tools. A nonparametric Spearman statistic correlation test was used to compare a large number of relevant dose histogram points, and to establish the relationship between dose statistics for walled and solid structures. Several notable relationships were observed. Maximum rectal dose was strongly correlated between the solid structure and both the 2D-generated (Spearman's correlation rs = 0.988, p < 0.01) and 3D-generated (rs = 0.952 p< 0.01) wall structures. This indicates that the rectal hot spot occurred in or near the wall for all cases, suggesting that both structure types give similar maximum dose information for rectum. Maximum bladder dose was not significantly correlated between solid structures and the 2D (rs = 0.596, p= 0.069) and 3D-generated (rs = 0.681, p= 0.03) counterparts. This suggests that the maximum dose is not consistently in or near the bladder wall. This favors the use of bladder wall contours when considering bladder toxicity, with the maximum dose to the wall potentially being more relevant radiobiologically. This analysis was extended to many other relevant points on the rectum and bladder histogram curves. Where correlations are strong, equations of best-fit are presented. This work establishes several statistically-significant relationships between bladder and rectum DVHs and DWHs for VMAT irradiation of intermediate-risk prostate cancer. This information may be used to inform contouring requirements for clinical trial design as well as for standard patient care.

Irradiation-induced BCC-phase formation and magnetism in a 316 austenitic stainless steel

Abstract Specimens of austenitic stainless steel were irradiated with 6 MeV Xe ions to two doses of 7 and 15 dpa at room temperature and 300 °C respectively. Then partial irradiated specimens were subsequently thermally annealed at 550 °C. Irradiation-induced BCC-phase formation and magnetism were analyzed by grazing incidence X-ray diffraction (GIXRD) and vibrating sample magnetometer (VSM). It has been shown that irradiation damage level, irradiation temperature and annealing temperature have significant effect on BCC-phase formation. This BCC-phase changes the magnetic behavior of austenitic stainless steel. The stress relief and compositional changes in matrix are the driving forces for BCC-phase formation in austenitic stainless steel during ion irradiation.

Evaluation of displacement cross-section for neutron-irradiated 15-15Ti steel and its swelling behavior in CiADS radiation environment

We report on the proposed method of evaluating the displacement cross-sections in NRT and BCA-arc-dpa models. The method is based on the NJOY code in conjunction with the IOTA code and is applicable to neutron energy in the range of 0.1 neV–20 MeV, defined by using NJOY and nuclear library files with data up to 20 MeV. The displacement cross-section has been calculated for natural iron, 15-15Ti, 316L, Eurofer, ODS, and T91 steels. The displacement cross-sections for 15-15Ti steel were used to estimate radiation damage and swelling level under irradiation conditions of the China Initiative Accelerator Driven System (CiADS) subcritical core. The swelling analysis has shown, that in CiADS radiation environment, the 15-15Ti steel has a good margin to cladding failure due to swelling and, therefore, might be a cladding material for CiADS.

Thermal annealing characteristics of fission tracks in natural zircons of different ages

AbstractFission track (FT) thermochronometry using zircon has widely been applied to the resolution of a variety of geologic problems, for which the understanding of FT annealing behaviour is essential. Thermal annealing experiments were conducted on FTs in natural zircons having different ages (ranging from ~0.6 to ~70 Ma) and radiation damage levels. We measured horizontal confined track lengths on nine zircon concentrates separated from rapidly cooled volcanic rocks, after 1 hr annealing at 400–700°C. As the annealing temperature increases, the observed tracks show a consistent and systematic length reduction in all samples, and the mean track lengths are hardly distinguishable among the nine samples for the same annealing step. Our results suggest that the thermal annealing characteristics at laboratory time‐scale are concordant among the zircons, regardless of their ages, and that identical annealing kinetics may work for Late Mesozoic to Cenozoic zircons.

Обеспечение микробиологической безопасности пищевой продукции с применением ионизационного облучения

Работа посвящена обоснованию возможности применения ионизирующего облучения в пищевой отрасли с целью снижения микробиологической обсемененности сельскохозяйственной и пищевой продукции в процессе использования и долгосрочного хранения. Целью данных исследований является обоснование возможности применения радиационного облучения в пищевой отрасли. В исследование по эффективности угнетения микроорганизмов использовали следующие штаммы: Escherichia coli ATCC полученный из штамма ВКМ В 114191, Staphylococcus aureus ATCC 25923 (f-49)2 полученный из штамма ВКМ201189 и Salmonella entrica subsp. Enterica serovar Typhimurium ATCC 140283. Облучение проводили на ускорителе УЭЛВ-10-10-С-70 Центра коллективного пользования физическими методами исследования в «Институте физической химии и электрохимии им. А.Н. Фрумкина Российской Академии Наук». Результаты исследований показали зависимость устойчивости изучаемых штаммов микроорганизмов. Исследования показали, что наиболее устойчивыми к ионизационному облучению являются штамм Salmonella и E. coli, меньше устойчив штамм микроорганизмов S. aureus. Зависимость количества микроорганизмов от дозы облучения носит немонотонный, полимодальный характер – при обработке тест культур ионизационным облучением от 4 до 5 кГр наблюдается увеличение роста микроорганизмов для всех условий обработки, и только затем их ингибирование. При увеличении доз облучения свыше 5 кГр уровень возникающих клеточных радиационных повреждений будет превышать возможности снижения их защитными механизмами клетки и кривые доза–эффект будут соответствовать обычной линейной или квадратично-линейной функции. Снижение количества клеток при облучении до 4 кГр можно объяснить тем, что при низких дозах, сравнимых с уровнем естественной радиации, степень повреждения ДНК микроорганизмов слишком мала, чтобы активизировать адекватный уровень ферментативной репарации.

Radiation-Damaged Tungsten: Production and Study in a Steady-State Plasma Flux

The effect of deuterium plasma on tungsten with high levels of radiation damage was studied experimentally. Tungsten was examined as a candidate plasma-facing material for a fusion reactor. The effect of damage accumulation in a material irradiated with fusion neutrons was simulated using high-energy ions. Primary radiation defects of 1–100 dpa were produced in tungsten irradiated with He2+ and C3+ ions accelerated to 3–10 MeV in the cyclotron at the Kurchatov Institute with a fluence of 1017–1019 ion/cm2. The irradiated material was exposed to deuterium plasma at the LENTA linear plasma facility operated in the continuous regime and providing a plasma flux of 1021–1022 D/cm2. The erosion dynamics, the development of surface microstructure, and the accumulation of deuterium in tungsten were studied. Enhanced retention of deuterium was observed in the samples damaged both by helium and carbon ions at room temperature (ERDA). The effect of deuterium retention was suppressed in the damaged tungsten samples processed at a temperature of 500°C.

Defect-interface interactions in irradiated Cu/Ag nanocomposites

In this work, we employ transmission electron microscopy and helium ion irradiation to study the response of biphase interfaces to radiation induced point defect fluxes from the two adjoining phases. Analysis of interface-affected defect accumulation was carried out over a wide range of radiation damage levels from near zero displacement per atom (dpa) to 16 dpa and helium concentrations of 0 at.% to 8 at.%. Results show a strong interface density dependence in which Cu/Ag interfaces in the nanolayered regions spaced <500 nm were remarkably microstructural stable over the entire range without accumulating micro-scale defects, while those spaced >1 μm apart were destroyed. We report the concomitant development of a bubble-free zone in Cu that was independent of defect levels and interface-contacting bubbles zone in Ag. This finding is explained by bias segregation to the interface of interstitials from Ag and vacancies to misfit dislocation nodes in the interface from Cu. The point defect transfer across the interface can be explained by the spatial variation in interface pressure within the interface and gradient in pressure across the interface, both originating from the lattice mismatch and surface energy difference between the two crystals.