Unirradiated Counterparts Research Articles

Effects of Ion Irradiation and Temperature on Mechanical Properties of GaN Single Crystals under Nanoindentation.

Understanding the impact of irradiation and temperature on the mechanical properties of GaN single crystals holds significant relevance for rational designs and applications of GaN-based transistors, lasers, and sensors. This study systematically investigates the influence of C-ion irradiation and temperature on pop-in events, hardness, Young's modulus, and fracture behavior of GaN single crystals through nanoindentation experiments. In comparison with unirradiated GaN samples, the pop-in phenomenon for ion-irradiated GaN samples is associated with a larger critical indentation load, which decreases with increasing temperature. Both unirradiated and ion-irradiated GaN samples exhibit a decline in hardness with increasing indentation depth, while Young's moduli do not exhibit a clear size effect. In addition, intrinsic hardness displays an inverse relationship with temperature, and ion-irradiated GaN single crystals exhibit greater intrinsic hardness than their unirradiated counterparts. Our analysis further underscores the significance of Peierls stress during indentation, with this stress decreasing as temperature rises. Examinations of optical micrographs of indentation-induced fractures demonstrate an irradiation embrittlement effect. This work provides valuable insights into the mechanical behavior of GaN single crystals under varying irradiation and temperature conditions.

Effect of irradiation-induced strength anisotropy on the reorientation trajectories and fragmentation behavior of grains in BCC polycrystals under tensile loading

We present a combined experimental and computational study exploring the effects of strength anisotropy on the grain reorientation trajectories in neutron-irradiated BCC polycrystals subjected to uniaxial tensile loading. We observe through in situ high-energy X-ray diffraction microscopy measurements of a model BCC alloy, Fe-9wt.%Cr, that the grains in irradiated samples exhibit reorientation trajectories that deviate more substantially from classical expectations than those in the unirradiated counterpart. We hypothesize that irradiation-induced strength anisotropy is a major influence on this behavior. Utilizing crystal plasticity finite element modeling, we isolate the effects of strength anisotropy by performing a suite of simulations in which we systematically strengthen select slip systems. Reorientation trajectories are compared against a datum of Taylor model predictions, and the deviation from classical expectations is analyzed through the lens of slip activity and availability. We further describe observations regarding the propensity of samples with high degrees of strength anisotropy to exhibit grain fragmentation. Overall, computational results provide insight on and quantification of the effects of strength anisotropy on reorientation trajectories and grain fragmentation, and align well with experimental observations, suggesting strength anisotropy as a plausible contributing mechanism to the observed phenomena.

Irradiation damage and corrosion performance of proton irradiated 304 L stainless steel fabricated by laser-powder bed fusion

The irradiation-induced microstructure and corrosion performance of proton irradiated 304 L stainless steel (SS) fabricated by laser powder bed fusion (LPBF) is investigated. Irradiation-induced dislocation loops are observed in both LPBF and traditionally manufactured (TM) 304 L SS following 2 MeV proton irradiation at 360 °C. A comparison analysis of the oxide scales formed on proton irradiated LPBF and TM 304 L SS is conducted along with the unirradiated counterparts. The irradiation-induced defects accelerate the corrosion by providing a rapid diffusion path to form a thicker and more porous film with a double-layer structure and herein the oxide film thickness of TM 304 L SS is approximately twice that of the LPBF 304 L SS. The unique microstructure of high dislocation densities, cellular sub-grains boundaries and dispersed nanoscale inclusions provides large amounts of interfaces in LPBF samples, which is benefit to absorb the irradiation-induced point defects. The irradiation induced fast diffusion paths and the nucleation points of oxides are thus reduced, resulting in a thinner oxide film thickness and a better corrosion resistance revealed by the more Cr enrichment of inner scale in LPBF 304 L SS.

Molecular dynamics study of the tensile properties of gold nanocrystalline films irradiated by gallium Ions

Understanding the effects of heavy ion irradiation on the tensile properties of metals at the nanoscale is important for the development of nanomechanical and other nanodevices using focused ion beam fabrication. This is both in terms of achieving the expected performance of designed devices and in potentially exploiting changes in mechanical properties to develop novel device concepts. We report investigation of the tensile properties of gold nanocrystalline films bombarded by high-energy Ga ions using molecular dynamics calculations. Ga ion irradiation leads to multiple grains with the redistribution of the grain boundaries (GBs). Importantly, Ga ion irradiation causes the film to become less ductile and more prone to fracture. The main reason is not surface damage caused by the sputtering effect of high-energy particles, but the convergence of GBs to the surface crater. On the other hand, for porous films with micropores in the GBs, irradiation results in the hardening of film and the ultimate tensile strength is larger than that of unirradiated counterpart.

Clarifying the mitigation effect of proton irradiation on the intergranular oxidation of 316L stainless steel in high temperature water

The role of proton irradiation in the intergranular oxidation of 316L stainless steel after long-term immersion in simulated PWR primary water was clarified by comparing the microstructural and microchemical features of oxide between the irradiated grain boundary (GB) and its un-irradiated counterpart. As such, the interference from difference in GB structure can be ruled out. Surprisingly, the results reveal that the intergranular oxide penetration in the irradiated region is shallower than that in the un-irradiated region. It is found that Si segregated at the irradiated GB diffuses outwards preferentially and gets oxidized due to its high diffusivity and affinity to oxygen. The Si-enriched oxide in the intergranular oxide tip of irradiated GB can act as a temporary diffusion barrier for oxygen, although it tends to dissolve near the sample surface. Meanwhile, the efficiency of elements (especially Cr) transport along irradiated GB to the oxidation front is promoted mainly due to the vacancies created by preferential diffusion of Si, resulting in higher Cr content at the intergranular oxide tip. The combination of Si and Cr enrichments in the intergranular oxide tip can enhance the resistance to oxidation and eventually leads to a lower oxidation rate for the irradiated GB. For the first time, our study determines that irradiation can enhance the intergranular oxidation resistance of stainless steel after long-term immersion in simulated PWR primary water when the sample is not stressed.

Gamma radiation-induced photoluminescence in calcium phosphate glass and inhibiting effect from copper

The influence of gamma-ray irradiation on the optical properties of 50P2O5–30CaO–20Na2O glass and quaternary ones prepared with [CuO]/[Na2O] molar ratios of 0.1, 0.7 and 1.5 at fixed [P2O5]/[CaO] is reported. The glasses prepared by melting were subjected to 100 kGy Co-60 gamma ray irradiation and studied by optical transmission and photoluminescence (PL) spectroscopy. The gamma-irradiated 50P2O5–30CaO–20Na2O ternary developed a ruby-red color and showed absorption features around 425 and 500 nm attributed to oxygen hole centers. The quaternary with [CuO]/[Na2O] molar ratio of 0.1 merely showed a weak absorption feature around 425 nm, whereas the highest molar ratios did not show significant differences relative to the pristine. Analyses of band gap and Urbach energies were made to aid in evaluating radiation-induced changes. Further, the irradiated copper-free glass exhibited a distinct blue luminescence band around 415 nm (not observed prior). It was most favorably excited in the UV at 265 nm, suggesting a phosphorus electron center at its origin. Its decay kinetics appeared relatively slow with a first-order exponential decay with lifetime of 4412 (±4) μs. Conversely, such emission was not detected for the copper-containing glasses, which instead exhibited PL properties comparable to the unirradiated counterparts. Finally, the effect of heat treatment after the gamma ray exposure was evaluated. The radiation-induced color centers showed a bleaching effect whereas the new PL vanished thus supporting the defects-related origin.

Effect of annealing and irradiation on the evolution of texture and grain boundary interface in electrodeposited nanocrystalline nickel of varying grain sizes

Ni coatings applied on structural alloys of molten-salt reactors have been shown to enhance corrosion resistance. Due to inherent advantages, the application of electrodeposited (ED) nanocrystalline Ni coatings could provide a progressive upgrade. The effectiveness, however, relies on the production of favorable microstructural attributes for corrosion resistance and their stability in a high-temperature radiation environment. The present study compares the annealed microstructure of electrodeposited nanocrystalline Ni of varying grain sizes: 20 nm, 50 nm, 100 nm and 200 nm. EBSD studies of samples annealed at 650 °C revealed a strong texture of 〈001〉//ED fiber component accompanied by the formation of Σ3 twin boundaries. A high fraction of Σ3 twin boundaries desirable for corrosion resistance is found in samples with initial grain sizes of 20 nm and 50 nm. The irradiation stability of as-deposited 20 nm and 50 nm grain-sized samples was evaluated using ion irradiation at 550 °C and compared with unirradiated counterparts that had experienced annealing at the same temperature. Irradiation causes a marginal increase in grain growth and 〈100〉 texture, and a slight decrease in Σ3 twin fractions. The desirable microstructural attributes for corrosion resistance are largely preserved up to displacement damage of 18.5 dpa in 20 nm and 50 nm grain-sized samples.

Heavy-ion irradiation assisted modification of p-type transparent CuAlO2 films: Electrical, optical and thermoelectric properties

Heavy-ion (HI) irradiation is a unique approach to induce defects in semiconductor films. The ion irradiation leaves continuous columnar tracks to create various defects and reduce film density, modulating the thermoelectric properties of semiconductor films. As a p-type transparent oxide semiconductor (TOS), the as-synthesized CuAlO2 films were irradiated with different doses of Fe10+ ions at room temperature using the 320 kV High Voltage Platform, and then post-annealed to improve the microstructure and thermoelectric properties. The irradiated CuAlO2 films, with 15 × 1013 ions cm−2, can achieve an electrical conductivity of 0.14 S cm−1, which is about 200 times larger than the unirradiated counterparts. The Seebeck coefficient reaches up to 189.80 and 208.58 μV K−1 at room temperature and 600 K, respectively. Therefore, a high power factor (PF) of 9.15 μW m−1K−2 is rendered by the irradiated CuAlO2 films, whereas the unirradiated films are not detected in the given measurement range. The improved thermoelectric performance is mainly due to the increased copper vacancies in irradiated films without significantly reducing the crystallinity. The current work presents a promising strategy to improve the thermoelectric performance of semiconductor films.

Response in Cadmium Tolerance of Penicillium cyclopium Westling Subsequent to Exposure to Gamma Irradiation

Role of gamma irradiation in modulating 1.1 times more cadmium (Cd) tolerance in Penicillium cyclopium Westling has been detailed in this paper. Augmentation in metal tolerance was recognized by escalation in response to Cadmium and Cd removal efficacies than that of their un-irradiated group. FTIR spectra and electron microscopic photographs further strengthen the role of low absorbed dose of gamma in modulating Cd tolerance in P.cyclopium. Up regulated activities of anti-oxidatives in gamma exposed fungal groups might be the reason for enhanced Cd tolerance than that of their un-irradiated counter parts. This findings reveal a positive and eco-friendly step for heavy metal bioremediation and metal stressed lignocellulosic waste degradation.

High-energy synchrotron x-ray study of deformation-induced martensitic transformation in a neutron-irradiated Type 316 stainless steel

An unusual tensile deformation behaviour in the form of a propagating band along the sample gauge was observed in two neutron-irradiated 316 stainless steel samples during room-temperature tests, leading to a combination of high strength and high ductility. These bands were not observed in an unirradiated counterpart. With the help of in situ high-energy synchrotron x-ray diffraction, the phase-specific crystal information was tracked at different deformation levels in each sample. Post-irradiation and post-deformation samples were examined using electron microscopy to characterize various microstructural features. All samples displayed a deformation-induced martensitic phase transformation, which was identified as a second strain-hardening mechanism accompanying the dislocation hardening. The deformation-induced martensitic transformation was rationalized by the effect of applied stress on the effective martensite start temperature. The results showed that the irradiation did not alter the dislocation hardening and the martensitic transformation mechanisms, but the increased yield strength in irradiated materials facilitated the localized phase transformation at the onset of plastic deformation, in contrast to the unirradiated material which required pre-straining. The hardening effect of the martensitic transformation reduced the tendency towards necking and mitigated the loss of ductility in the irradiated material by carrying the deformation in the form of a propagating band. Despite the beneficial effect from the martensitic transformation, this study indicates that this mechanism cannot not be activated at typical operating temperatures of nuclear reactors.

MicroRNA-221/222 Inhibits the Radiation-Induced Invasiveness and Promotes the Radiosensitivity of Malignant Meningioma Cells.

The controversy of adjuvant radiotherapy of meningiomas is at least partially due to the insufficient understanding on meningioma cells' response to irradiation and the shortage of radiosensitivity-promotion methods. MicroRNA-221 and microRNA-222 were identified as critical regulators of radiosensitivity in several other tumors. However, their effect in meningiomas has yet to be confirmed. Therefore, the malignant meningioma IOMM-Lee cells were adopted, transfected with microRNA-221/222 mimics or inhibitors, and irradiated with different dosages. The effects of radiation and microRNA-221/222 were then assessed in vitro and in vivo. Radiation dose increases and microRNA-221/222 downregulation synergistically inhibited cell proliferation and colony formation, prevented xenograft tumor progression, and promoted apoptosis, but antagonistically regulated cell invasiveness. Pairwise comparisons revealed that only high-dose radiations (6 and 8 Gy) can significantly promote cell invasiveness in comparison with unirradiated counterparts. Further comparisons exhibited that downregulating the microRNA-221/222 expression can reverse this radiation-induced cell invasiveness to a level of untransfected and unirradiated cells only if cells were irradiated with no more than 6 Gy. In addition, this approach can promote IOMM-Lee's radiosensitivity. Meanwhile, we also detected that the dose rate of irradiation affects cell cycle distribution and cell apoptosis of IOMM-Lee. A high dose rate irradiation induces G0/G1 cell cycle arrest and apoptosis-promoting effect. Therefore, for malignant meningiomas, high-dose irradiation can facilitate cell invasiveness significantly. Downregulating the microRNA-221/222 level can reverse the radiation-induced cell invasiveness while enhancing the apoptosis-promoting and proliferation-inhibiting effects of radiation and promoting cell radiosensitivity.

Electron Irradiation Induced Multistage Martensitic Transformation in Ti‐Rich Ti−Ni Alloy

AbstractThis paper focuses on the microstructure and martensitic transformation of titanium−nickel (Ti−Ni) alloys under electron irradiation. There is no observable change of the microstructure after irradiation. Abnormal multistage martensitic transformations are observed in Ti‐rich Ti‐48 at % Ni alloys after electron irradiation. The three‐stage reverse martensitic transformation can be achieved in the irradiated alloy, while unirradiated counterpart displays normal one‐stage transformation during heating processes. The abnormal reverse martensitic transformation behavior caused by electron irradiation is due to the local stress field and the excessive defect concentration. The martensitic transformation behavior and temperature after annealing at 250 °C are consistent with the unirradiated counterpart. Additionally, the irradiated alloy exhibits superior thermal cycle stability to unirradiated samples.

Formation of multilayer structure and evolution of shape recovery characteristics in proton irradiated TiNi alloy thin films

TiNi thin films have attracted wide attentions as actuator materials in the micro-electro-mechanical systems (MEMs) for aerospace craft. However, multiple irradiation, such as the proton, was generally considered as an essential expired factor for the materials used in the aerospace. The present paper focused on the microstructure, martensitic transformation and shape recovery property of TiNi thin films after being irradiated by proton. A single layer structure B19′ phase to a dual-phase (B2 and B19′) with multilayer structure after proton irradiation have been revealed through a combination technique of grazing incidence (GI) XRD and TEM. As-formed irradiated films with amorphous layer and B2 austenite phase displayed a two-step martensitic transformation behavior, which occurred in the irradiated and the unirradiated layer. In contrast, the unirradiated counterparts just exhibited a single-step martensitic transformation. In addition, some defects could be seen after the TiNi films being irradiated. Such defects could induce a stress field that produces the R phase in the B2 phase. Furthermore, the synergistic effect of preferential sputtering effect and inverse Kirkendall effect induced the GP zones in the irradiated layer after 120 keV proton irradiation. The existence of amorphous phase and precipitation significantly deteriorated the shape recovery property.

Assessment of lead tolerance in gamma exposed Aspergillus niger van Tieghem & Penicillium cyclopium Westling

Purpose: Present study deals with the role of gamma irradiation in modulating lead (Pb) tolerance of Aspergillus niger van Tieghem. and Penicillium cyclopium Westling.Materials and methods: After being exposed to gamma absorbed doses those fungal strains were subjected to heavy metal uptake efficacies and anti-oxidative study. Fourier Transform Infrared (FTIR) spectra and Scanning Electron Microscopic (SEM) studies were also evaluated.Result: Gamma exposed A. niger & P. cyclopium showed enhanced growth in terms of colony forming unit (CFU) and more Pb uptake efficacies compared to their un-irradiated counterparts. FTIR spectra illustrated the involvement of functional groups in Pb biosorption. SEM photographs revealed the structural deformities in both the fungal strains after being exposed to Pb and gamma. Upregulated anti-oxidative defense system (super oxide dismutase, catalase, total glutathione) in gamma exposed fungal groups are accountable for enhanced Pb tolerance and removal than that of their un-irradiated counterparts.Conclusion: The outcomes of this study exhibit a light towards a new step of heavy metal bioremediation.

High-energy x-ray diffraction microscopy study of deformation microstructures in neutron-irradiated polycrystalline Fe-9%Cr

In this study, we used far-field high-energy x-ray diffraction microscopy (FF-HEDM) to measure in 3D the spatial distributions of the sizes, orientations, and residual strains of grains and subgrains formed by room-temperature tensile deformation in a neutron-irradiated (450 °C, 0.01dpa) Fe-9Cr specimen and its unirradiated counterpart. We found that neutron irradiation under this condition alone had no effect on the grain size distribution. After deformation, grains fragmented into subgrains in both unirradiated and irradiated specimens: the irradiated specimen contained a few large subgrains which co-existed with many smaller subgrains, while the unirradiated specimen contained small subgrains with a relatively uniform size distribution. Prior to deformation, the irradiated specimen had higher residual strain spread compared to its unirradiated counterpart, while after deformation to the maximum uniform elongation, the strain distributions among subgrains were similar between the unirradiated and irradiated specimens. The FF-HEDM measurements provide new insight into the effects of neutron irradiation on the mechanical response of Fe-Cr ferritic alloys.

Cardiac death rates after irradiation for esophageal cancer: An epidemiologic study among esophageal cancer survivors.

4049 Background: Esophageal cancer is frequently treated with radiation in addition to surgery and/or chemotherapy. Long-term survivors that received radiation may be at risk for radiation-induced cardiotoxicity. Methods: Esophageal cancer survivors (defined as surviving > 5 yrs after diagnosis) from all 18 Surveillance Epidemiology and End Results (SEER) registries from 1973 to 2013 were queried for irradiation status, cause of death and survival using SEERaBomb, a package for the R statistical programming language. Results: 6,514 esophageal cancer survivors were identified, of whom 2,892 (44%) received no radiation therapy and 3,448 (53%) received external beam radiotherapy. Mean age at the time of esophageal cancer diagnosis was 64.0 yrs in the no radiation group and 63.0 yrs in the radiation group. Median person years of follow up after esophageal cancer diagnosis was 8.6 yrs (interquartile range [IQR]: 7-12) in pts receiving no radiation and 7.9 yrs (6-11) in pts receiving radiation. A total of 590 esophageal cancer survivors died of cardiac disease; 254 received no radiation and 336 did receive radiation. Median time to cardiac death after esophageal cancer diagnosis was 32.2 yrs (IQR: 19-38) in pts that received no radiation and 25.3 years (15-30) in pts that received radiation (log-rank P< 0.001). Compared with unirradiated pts, irradiated pts had an increased risk of dying of cardiac disease (hazard ratio [HR] = 1.47; 95% confidence interval [CI]: 1.2-1.7, Cox regression P< 0.001). The association between radiation and cardiac death was the strongest in esophageal cancer pts diagnosed before 1995 (HR = 1.75; 95% CI: 1.4-2.2, P< 0.001) and in squamous cell carcinoma of the esophagus (HR = 1.9; 95% CI: 1.4-2.6, P< 0.001) but not in adenocarcinoma (HR = 1.04; 95% CI: 0.8-1.4, P= 0.8). Conclusions: 5-year esophageal cancer survivors that were treated with radiotherapy have an increased risk of dying of cardiac disease, compared with unirradiated counterparts. This association was strongest in pts treated before 1995 and in squamous cell carcinoma pts. This may be due to late radiation-induced cardiotoxicity, decreasing with the use of heart-sparing radiation techniques after 1995.

High-Temperature Corrosion Testing of Uranium Silicide Surrogates

The corrosion resistance of cerium silicide, a surrogate of uranium silicide, is investigated to gain insight into the reaction of uranium silicide with water. As-received and proton-irradiated Ce3Si2, CeSi2, and CeSi1.x monolithic pellets are subjected to corrosion tests in water at 300°C and 9 MPa for up to 48 h. Results show that an oxide layer composed of Ce4.67 (SiO4)3O forms on the surface of all samples, and it grows thicker with extended exposure times. Irradiated samples corrode to a greater extent than their unirradiated counterparts, which is mainly a result of the existing post-irradiation cerium oxide and the presence of ion-induced defects. Most of the Ce3Si2 samples crack (as-received) or fracture (ion-irradiated) during testing, which is due to the brittleness of the samples and oxide erosion/spallation that occur during testing.

Unraveling The Origin of Enhanced Field Emission from Irradiated FeCo-SiO2 Nanocomposites: A Combined Experimental and First-Principles Based Study.

This work is driven by the vision of engineering planar field emitters with ferromagnetic metal-insulator nanocomposite thin films, using swift heavy ion (SHI) irradiation method. FeCo nanoparticles inside SiO2 matrix, when subjected to SHI get elongated. Using this, we demonstrate here a planar field emitter with maximum current density of 550 μA/cm(2) at an applied field of 15 V/μm. The film, irradiated with 5 × 10(13) ions/cm(2) fluence (5e13) of 120 MeV Au(9+) ions, shows very high electron emitting quantum efficiency in comparison to its unirradiated counterpart. Surface enhanced Raman spectroscopy analysis of unirradiated and 5e13 films further confirms that the field emission (FE) enhancement is not only due to surface protrusions but also depends on the properties of entire matrix. We find experimental evidence of enhanced valence band density of states (VB DOS) for 5e13 film from XPS, which is verified in the electronic structure of a model FeCo cluster from first-principles based calculations combining density functional theory (DFT) and molecular dynamics (MD) simulations. The MD temperature is selected from the lattice temperature profile inside nanoparticles as deduced from thermal spike model. Increasing the irradiation fluence beyond 5e13, results in reduced VB DOS and melting of surface protrusions, thus causing reduction of FE current density. We finally conclude from theoretical analysis that change in fluence alters the co-ordination chemistry followed by the charge distribution and spin alignment, which influence the VB DOS and concurrent FE as evident from our experiment.

Effect of Gamma Radiation on Zinc Tolerance Efficiency of Aspergillus terreus Thorn.

The present study emphasizes the potential of gamma radiation in enhancing zinc tolerance of Aspergillus terreus. Gamma-exposed A. terreus could tolerate 1.13 times more Zn, reflecting higher growth (in terms of CFU) under Zn stress and enhanced Zn removal efficacies than their unirradiated counterparts. Radiation-induced upregulation of antioxidative system (SOD, CAT, GSH and MT) of A. terreus is responsible for radiation-induced enhancement of Zn tolerance. FTIR spectra reveals the involvement of functional groups in Zn biosorption; SEM study divulges the structural changes due to metal and gamma exposure and SEM-EDX depicts the Zn uptake by A. terreus (both in gamma-exposed and unexposed conditions). This work sheds light toward utilizing low doses of ionizing radiation for making more metal-tolerant fungi and the possible mechanisms adopted by A. terreus for being more metallo-resistant.

Ionising Radiation in Modulating Zinc Tolerance Potential of Aspergillus niger

The present study describes the potential of gamma rays in enhancing zinc tolerance of Aspergillus niger. Gamma exposed group of A. niger showed 1.82 times more zinc tolerance than the unirradiated ones. Gamma exposed A. niger grown in different zinc enriched media, showed increase in growth (expressed in terms of colony forming unit), higher efficiency in zinc uptake and removal, when compared to that of their unirradiated counterparts. The present investigation throws light towards utilizing gamma radiation for formulating more metal-tolerant fungi for bioremediation.