Effect Of Induced Damage Research Articles

Impact of radiation damage on the photoconductor and photodiode properties of GaN core–shell p–n junction microwires

GaN nano- and microwires have gained increasing interest due to their unique geometry and flexibility, and have already been successfully applied in optoelectronics. One important advantage is their superior crystalline quality in comparison to their thin-film counterparts. Beside this, GaN is also known for its high radiation hardness, owed to the large displacement energy of the atoms in its crystal lattice and efficient dynamic annealing properties. In this work, single GaN core–shell p–n junction microwires have been processed into radiation detectors and the induced damage effects on the electrical and optoelectrical characteristics, when irradiating the detectors with 1 and 2 MeV protons, have been studied. By measuring the dark and photocurrent as a function of the irradiation fluence we show that for fluences up to 1×1014 protons/cm2 there is no significant modification of any of the parameters and that serious degradation only occurs for fluences above 1×1015 protons/cm2. Furthermore, we also observe that the dark current decays at a lower irradiation fluence with respect to the photocurrent due to the different impact of the created irradiation defects on the properties of the neutral region and the p–n junction. As a consequence, the signal-to-noise ratio of the detector is strongly enhanced, especially when applying a higher reverse bias. Thermal treatments furthermore show that the degree of recovery of the properties of the detectors is strongly dependent on the irradiation fluence. The detector irradiated with a fluence of 5×1014 protons/cm2 almost completely retrieved its pre-irradiation characteristics whereas the detector irradiated with 5×1015 protons/cm2 only showed a minimal recovery.

Histological study of the effect of hydroxychloroquine sulfate on the retina and the possible protective role of propolis in adult male albino rats

Background Hydroxychloroquine sulfate (HCS) is a widely used antimalarial drug. Recently, it garnered attention about its possible effect against COVID-19. Retinopathy is one of its dangerous side effects which may be untreated. Propolis is a substance made by honeybees and has a neuroprotective effect. Aim The study aimed to assess the impact of HCS on the retina and the possible ameliorative role of propolis in adult male albino rats. Materials and methods In all, 32 adult male albino rats were separated into four groups; group (I): the control group, group II: rats had received 100 mg/kg propolis for 12 weeks, group III: the HCS dose of 55 mg/kg/day had been administered to the rats for a period of 10 days, group IV: rats had received 55 mg/kg/day of HCS concomitant with 100 mg/kg propolis for 10 days and then propolis was continued to complete 12 weeks. Retinal specimens were obtained and processed for histological and morphometric analyses. Results Group III revealed vacuolations of photoreceptors; nuclei are widely separated in the outer and inner nuclear layers Also nuclei are darkly pigmented in the inner nuclear layer and the ganglion cell layer. Statistical analysis showed that there was a significant drop in the average number of ganglion cells when contrasted with the control group. These changes were markedly ameliorated in group HCS and propolis-treated group. Conclusion Hydroxychloroquine sulfate induced damaging effects on the rat retina and receiving propolis could attenuate these effects.

Proton irradiation induced damage effects in CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>-based perovskite solar cells

Perovskite solar cells (PSCs) have a great potential for space applications due to their high specific power, low cost and high defect tolerance. PSCs used in space will be subjected to high-energy particle irradiation, especially proton irradiation, resulting in the decline of photovoltaic (PV) performance. However, the research on proton irradiation effects in PSCs is still in its infancy stage. In this work, the CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> (MAPbI<sub>3</sub>) thin films and their PSCs are irradiated by protons with energy of 0.1, 2, 10, 20 MeV, etc. Irradiation-induced changes in PV parameters of the PSCs are studied as a function of proton fluence. The structural and surface morphological changes of the irradiated MAPbI<sub>3</sub> films and Au electrode layers of PSCs are characterized by X-ray diffraction and scanning electron microscopy. In addition, UV spectrophotometer is also employed to analyze the transmission loss in glass substrate induced by proton irradiation. It is found that PSCs exhibit superior resistance against proton irradiation. The PV properties of the PSCs don’t degrade after 0.1 MeV (2 MeV) proton irradiation up to a fluence of 1×10<sup>13</sup> p/cm<sup>2</sup> (1×10<sup>14</sup> p/cm<sup>2</sup>). The irradiation-induced damage in the charge transport layers may be the main cause for the performance degradation of PSCs. The gaseous products (NH<sub>3</sub> and CH<sub>3</sub>I) of perovskite decomposition eventually lead to exfoliation of the top Au electrode from the PSCs. Regarding 10 and 20 MeV proton irradiation with larger projected ion ranges, the irradiations create color center defects in glass substrate of PSCs, which results in a decrease in light transmission of visible spectrum. However, the color center defects, specifically non-bridging oxygen hole centers, will be partly annealed at room temperature or 100 ℃, reducing the transmission loss in glass. The reported results may help predict the performance degradation of PSCs in space irradiation environment.

Paraquat-induced cholesterol biosynthesis proteins dysregulation in human brain microvascular endothelial cells

Despite Paraquat (PQ) being banned in several countries, it is still one of the most commonly used herbicides in agriculture. This compound is known to induce damaging effects on human and animal brain cells by generating Reactive Oxygen Species (ROS). However, there is few evidence of PQ effect on Human Brain Microvascular Endothelial Cells (HBMECs), one of the major component of the Blood–Brain Barrier (BBB). The present study aimed at unraveling biological mechanisms associated to the exposure of 1, 10 and 100 µM of PQ for 24 h on HBMECs. High-throughput mass spectrometry-based proteomics using data-independent acquisition (DIA) was applied. Biological pathway enrichment and cellular assays such as mitochondrial respiration and cholesterol level were performed to verify proteomics results. A total of 3753 proteins were quantified out of which 419 were significantly modulated by paraquat exposure. Biological pathway enrichment revealed the ubiquinone metabolism, a pathway directly linked to mitochondrial complex I proteins, confirming the well-known mechanism of PQ inducing oxidative stress. Additionally, this study also described the cholesterol biosynthesis modulation on HBMECs not yet described. In conclusion, our data indicate the toxic effect of PQ on HBMECs by downregulating proteins involved in mitochondrial complex I and cholesterol pathways.

Priming with 5-aminolevulinic acid (ALA) attenuates UV-B induced damaging effects in two varieties of Cajanus cajan L. seedlings by regulating photosynthetic and antioxidant systems

The objective of this study is to investigate whether pre-treatment (priming) of chlorophyll precursor 5-aminolevulinic acid (ALA) assumes a huge part in moderating harms caused by UV-B exposure on two varieties of Cajanus cajan L. seedlings namely BAHAR and KB-17. Healthy seeds were primed with two doses of ALA (lower dose: ALA1; 25µM and higher dose: ALA2; 100 µM) for 24 h at 25±2 °C and thereafter 17-day old seedlings were exposed to an enhanced dose of UV-B radiation i.e. 2.2 kJ m−2d−1. Results showed that UV-B exposure significantly declined growth attributes, photosynthetic pigments (chlorophyll a, b and carotenoids contents), photosynthetic gas exchange characteristics (A, Ci, Gs, E, and WUE). This decrease was also accompanied by the accumulation of reactive oxygen species: superoxide radical (SOR; O₂˙ˉ), hydrogen peroxide (H2O2), and lipid peroxidation (MDA contents). The antioxidative enzyme activities: catalase (CAT), superoxide dismutase (SOD), glutathione-S-transferase (GST), and peroxidase (POD) and non-enzymatic antioxidants: total phenolics content (TPC) and total flavonoids content (TFC) were increased. On contrary to this, damaging effects of UV-B radiations were markedly alleviated with the exogenous application (priming) of ALA by enhancing plant growth and growth-regulating parameters. Furthermore, ALA application decreased the UV-B induced oxidative stress in Cajanus cajan L. seedlings by further improving the activity of enzymatic and the contents of non-enzymatic antioxidants of test plant defense system. Furthermore, priming with ALA decreased the germination time and increased the germination index which additionally served as a significant purpose behind the improvement in the harvest quality and amount. The BAHAR variety of Cajanus cajan was discovered to be more tolerant against UV-B stress due to its more efficient defense system with a higher rate of antioxidant enzyme activities. On the other hand, KB-17 variety of Cajanus cajan was discovered to be sensitive against UV-B stress due to its feeble defense system with higher accumulation of reactive oxygen species. Thus, these findings suggest that priming of seeds with ALA act as a sustainable remedial strategy in reducing the hazardous effects of UV-B induced stress on crop productivity of Cajanus cajan seedlings by triggering the up-regulation of photosynthesis and antioxidant system to counterbalance the ROS-mediated damage to macromolecules.

Ameliorative Effect of Gum Acacia on Water Pipe Smoke ‐ Induced Testicular Impairment in Mice

We investigated some effects of water pipe smoke (WPS) exposure (30 min/day, for 30 days) in male mice, and the possible ameliorative of gum acacia (GA) coadministration thereon. Controls were exposed to air‐only (AE). Twenty‐four hours post last exposure, the levels of some plasma reproductive hormones, biochemical markers of inflammation, oxidative and nitrosative stress and testicular histopathology were assessed. The concentration of cotinine, the predominant metabolite of nicotine, was also measured in urine. WPS exposure induced a significant decreases in testosterone, estradiol, luteinizing hormone, and androgen binding protein. Inhibin B concentration was significantly increased. Plasma alkaline phosphatase, lipopolysaccharide binding protein, uric acid, and lactate dehydrogenase were all significantly increased following WPS exposure. In testicular homogenate, NF‐κB p65, Nrf2, interleukin‐1β, interleukin‐6, tumor necrosis factor –α, and transforming growth factor‐β1 were all significantly elevated after WPS exposure. WPS exposure decreased nitrite and total nitrite, glutathione reductase activity, and increased lipid peroxidation, cytochrome C, and 8‐Oxo‐2′‐deoxyguanosine. Histopathologically, there was slight reduction in the diameter of the seminiferous tubules with disorganized spermatogenesis. Cotinine concentration was significantly increased in the WPS‐exposed group compared with the control group. GA co‐administration mitigated the adverse actions of WPS measured. We conclude that daily exposure to WPS at the above dose induced damaging effects to the reproductive system in male mice, and that GA co‐administration mitigated the adverse actions of WPS measured.Support or Funding InformationSupported by a joint grant from Sultan Qaboos University and United Arab Emirates University (CL/SQU ‐ UAEU/18/01).

Quantification of the constitutive relationship of high-energy heavy-ion irradiated SS316L using the small punch test

Heavy-ion irradiation has been widely used to simulate neutrons-irradiation induced damage effects, due to its higher damage rate and lower activation of the post-irradiation manipulation. The high-energy ion beam is capable of producing a thickness of dozens of microns damaged region in steel, making it possible to evaluate the macroscopic mechanical properties of the irradiated specimens. In the present paper, a method to quantify the constitutive relationships of high-energy heavy-ion irradiated steels is proposed. Ni22+ ions with a kinetic energy of 357.86 MeV provided by a cyclotron were used to produce a quasi-homogeneous atomic displacement damaged layer (about 25 μm in thickness) in specimens of 316 L stainless steel. The temperature of the specimens were kept at about −50 °C during ion irradiation. Two damage levels of 0.16 and 0.33 displacement per atom (dpa) were approached. Small punch test of the unirradiated and irradiated ϕ3 mm disk samples was carried out to obtain the load-deflection curves. A series of finite element simulation of SPT of the laminated irradiated samples, in combination with sequential programming algorithm, was performed to characterize the constitutive relationships of the irradiation damaged layer of the samples. Finite element simulations with obtained constitutive relationships show agreement with the experimental results. Nanoindentation tests were carried out to verify the identified constitutive relationships. The nanoindentation results show an irradiation induced hardening in good agreement with that from the obtained constitutive relationships.

Ameliorative Effects of Thymoquinone on Sperm Parameters and Testosterone Level of Nicotine-Treated Sprague Dawley Rats

Abstract Thymoquinone (TQ), the main constituent of the volatile oil derived from Nigella sativa has shown pharmacological benefits against various diseases while nicotine is an active component in cigarette that is known to be detrimental. This study was conducted to assess the ameliorating effects of TQ on sperm count, membrane, mitochondria and testosterone of nicotine-treated rats. Rats were randomized into four groups: control, nicotine, TQ, and nicotine with TQ. Nicotine (5 mg/kg bwt/day) was subcutaneously injected for 30 days to induce damaging effects on sperm and testosterone level. Rats were force-fed with TQ (5 mg/kg bwt/day) for the following 30 days. Sperm count was reduced in the nicotine group (26.72 ± 1.64 106/mL) but showed a significantly higher number in the nicotine+TQ group (30.97 ± 0.88 106/mL; p<0.05). Results of sperm membrane integrity test and number of MitoTracker positive sperm also showed a significantly lower percentage in the nicotine group (47.34 ± 0.69 % and 75.68 ± 0.90 %, respectively) but a notable improvement in the nicotine+TQ group (52.58 ± 1.14 % and 79.08 ± 0.74 %, respectively). Testosterone concentration showed elevation in the nicotine+TQ group (7.61 ± 0.51 ng/mL) compared to the nicotine group (5.71 ± 0.15 ng/mL). TQ demonstrated ameliorative potential against the detrimental effects of nicotine towards sperm count, membrane, mitochondria and testosterone level.

Histological and Immunohistochemical Study of the Effect of Alendronate on the Submandibular Salivary Gland of Adult Male Albino Rat and the Possible Protective Effect of Propolis

AbstractBackground: Alendronate is an anti-bone-resorptive drug used in the treatment of post-menopausal osteoporosis. Its long administration induced organ damage especially the submandibular salivary glands. Propolis is a natural resinous substance with an antioxidant and anti-inflammatory actions.Aim of Study: This work was performed to study the effect of alendronate on the histological structure of the submandib-ular salivary gland of adult male albino rat and the possible protective effect of propolis.Material and Methods: 40 adult male albino rats were divided into 4 groups (10 rats each); control group, Group A: Rats received 100mg/kg body weight propolis, Group B: Rats received 2.5mg/kg body weight alendronate and Group C: Rats received propolis 30 minutes before alendronate. Doses were given orally for consecutive 30 days then gland specimens were taken for histological and immunohistochemical studies using light and electron microscopes.Results: H & E and toluidine blue results of Group B revealed disturbed architecture, separated lobules and acini, cytoplasmic vacuolations, dark nuclei, irregular ducts and congested blood vessels. PAS-AB showed significant increase in its mean color intensity as compared with control group while a-SMA glandular myoepithelial cells immunostaining expressed significant decrease in its mean color intensity in comparison to control group. Electron microscopic examination of acinar and duct cells revealed cytoplasmic vacuolations, rarefaction, abnormal shaped mitochondria with lost cristae, electron dense bodies, dilated RER and Golgi apparatus, apparently increased secretory granules with coalescence, compressed shrunken hyperchromatic nuclei, nuclear mem-brane irregularities, and dilated perinuclear and intercellular spaces. Group C showed moderate improvement of the previ-ous pathological findings.Conclusion: Alendronate induced damaging effects on the histological structure of submandibular salivary gland in rats and the administration of propolis could moderately improve such damage through its anti-oxidant and anti-inflammatory effects.

The Propolis Effect on Chlorpyrifos Induced Thyroid Toxicity in Male Albino Rats

Chlorpyrifos (CPF) is a chlorinated organophosphate insecticide that is used widely in the world and Egypt. The aim of present work was to study the possible protective role of Propolis on thyroid gland of male rats after chronic exposure of chlorpyrifos. For this purpose, Fifty adult male albino rats were randomized into 5 groups: I, II (Control), III (received Propolis dissolved in 0.5 ml corn oil, 50 mg/kg b.w./day), IV (received CPF dissolved in 0.5 ml corn oil 6.75 mg/kg b.w./ day) and V (received CPF and Propolis at the same previously mentioned doses). Rats were orally treated by gavage for 12 weeks. We found that Chlorpyrifos induced damaging effects in thyroid tissue architecture, thickened collagen fibers between the follicles and decreased periodic acid schiff (PAS) reaction in the colloids. Immunohistochemically, there was weak thyroglobulin (TGB) expression. Besides, it significantly decreased the serum levels of Tri-iodothyronin (T3), Tetraiodothyronin (T4) and Thyroid stimulating hormone (TSH). It depressed reduced glutathione (GSH) content and antioxidant enzyme activities in thyroid tissues with respect to control groups. Furthermore, CPF increased thyroid oxidative stress as manifested by elevated malondialdehyde (MDA) levels. On the other hand, the concurrent administration of Propolis with CPF showed significant improvement in previous changes. Our findings showed that the concurrent oral administration of Propolis with CPF improved the CPF induced oxidative damaging effects in thyroid gland and the antioxidative defense in the rats.

Machinability of Continuous-Discontinuous Long Fiber Reinforced Polymer Structures

In the present paper a new material system which combines the properties of continuous and discontinuous fibers (CoDiCoFRP) is investigated. The machinability and the induced damage effects of six material variations are investigated for a milling process at various cutting speeds and feed rates with an uncoated cemented carbide tool. The resulting forces and cutting torque were measured and analyzed for each material. After the milling process, the surface layers of the specimens were analyzed to quantify damage introduced during the milling process. The results show a strong influence of the material structure on the machining forces and damage.

Sulphur alters chromium (VI) toxicity in Solanum melongena seedlings: Role of sulphur assimilation and sulphur-containing antioxidants

The present study investigates modulation in hexavalent chromium [Cr(VI) 25 μM] toxicity by sulphur (S; 0.5, 1.0 and 1.5 mM S as low (LS), medium (MS) and high sulphur (HS), respectively) in Solanum melongena (eggplant) seedlings. Biomass accumulation (fresh and dry weights), photosynthetic pigments, photosynthetic oxygen evolution and S content were declined by Cr(VI) toxicity. Furthermore, fluorescence characteristics (JIP-test) were also affected by Cr(VI), but Cr(VI) toxicity on photosystem II photochemistry was ameliorated by HS treatment via reducing damaging effect on PS II reaction centre and its reduction side. Enhanced respiration, Cr content and oxidative biomarkers: superoxide radical, hydrogen peroxide, lipid peroxidation and membrane damage were observed under Cr(VI) stress. Though Cr(VI) enhanced adenosine triphasphate sulfurylase (ATPS) and o-acetylserine(thiol)lyase (OASTL), glutathione-S-transferase (GST), glutathione reductase (GR) and ascorbate peroxidase (APX) activity, and content of total glutathione, cysteine and NP-SH, however, their levels/activity were further enhanced by S being maximum with HS treatment. The results show that Cr(VI) toxicity does increase under LS treatment while HS protected Cr(VI)-induced damaging effects in brinjal seedlings. Under HS treatment, in mitigating Cr(VI) toxicity, S assimilation and its associated metabolites such as cysteine, glutathione and NP-SH play crucial role.

Biochemical Changes Induced by Gamma Irradiation in the Ground Beetle Blaps polycresta

The exposure to low-dose gamma radiation from natural sources is a continuing and inescapable feature and it is common in certain occupations. The present study was designed to investigate the effects of low-dose gamma radiation on some detoxification enzymes such as; AST, ALT, ACP, ALP, GSH, GPX, SOD and CAT, as well as, its effect on total protein and DNA content in the soft tissues homogenate of male’s ground beetle Blaps polycresta. Insects were divided into three groups (group A, B and C) of 10 beetles each. Two groups (group B and C) were irradiated with doses at a rate of 32 Gy and 64 Gy; group A was considered as the control group. The study revealed a dose-dependent effect on the tested parameters. Significant increase in the enzyme activity of AST, ALT, ACP and ALP were observed in group B and C respectively compared to the control group (group A). The findings also showed a significant inhibitions in the enzymatic activity of GSH, GST, GPX, SOD and CAT in the irradiated groups compared to the control group. Furthermore, their radiated groups reported a decrease in protein and DNA content compared to the control group. Our observations suggested that the genotoxic effects of gamma radiation induced damaging effects on enzyme molecules, protein and nucleic acid (DNA) and may explain the increase in health risk from high doses of ionizing radiation.

Whole-exome sequencing identifies multiple loss-of-function mutations of NF-κB pathway regulators in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is an epithelial malignancy with a unique geographical distribution. The genomic abnormalities leading to NPC pathogenesis remain unclear. In total, 135 NPC tumors were examined to characterize the mutational landscape using whole-exome sequencing and targeted resequencing. An APOBEC cytidine deaminase mutagenesis signature was revealed in the somatic mutations. Noticeably, multiple loss-of-function mutations were identified in several NF-κB signaling negative regulators NFKBIA, CYLD, and TNFAIP3 Functional studies confirmed that inhibition of NFKBIA had a significant impact on NF-κB activity and NPC cell growth. The identified loss-of-function mutations in NFKBIA leading to protein truncation contributed to the altered NF-κB activity, which is critical for NPC tumorigenesis. In addition, somatic mutations were found in several cancer-relevant pathways, including cell cycle-phase transition, cell death, EBV infection, and viral carcinogenesis. These data provide an enhanced road map for understanding the molecular basis underlying NPC.

Protective role of gamma amminobutyric acid on Cassia italica Mill under salt stress

The present study was conducted to evaluate the effect of salinity stress on growth of Cassia italica and role of gamma amminobutyric acid (GABA) in mitigating the salt stress induced damaging effects. Antioxidant activity, level of endogenous growth hormones and other biochemical parameters were evaluated. Salt stress enhanced the production of reactive oxygen species (ROS) resulting in the enhanced lipid peroxidation which was however reduced by application of GABA. Increased lipid peroxidation in salt stressed plants caused an obvious reduction in the total lipid content as compared to GABA treated plants. The antioxidant enzymes were higher in GABA treated plants which indicated a reduction of oxidative damage. The concentrations of growth hormones like indole acetic acid (IAA), indole butyric acid (IBA), gibberellic acid-1 (GA1), and gibberellic acid-4 (GA4) were reduced by salt stress, while enhanced by GABA treatment. In addition GABA treated plants maintained lower levels of sodium and chloride ions as compared to salt stressed plants. It could be concluded that toxic effects of salt stress on growth, antioxidant system, hormones and mineral nutrients in Cassia italica could be alleviated by exogenous application of GABA.

Is Ionizing Radiation Harmful at any Exposure? An Echo That Continues to Vibrate.

The health risks to humans and non-human biota exposed to low dose ionizing radiation remain ambiguous and are the subject of intense debate. The need to establish risk assessment standards based on the mechanisms underlying low-level radiation exposure has been recognized by regulatory agencies as critical to adequately protect people and to make the most effective use of national resources. Here, the authors briefly review evidence showing that the molecular and biochemical changes induced by low doses of radiation differ from those induced by high doses. In particular, an array of redundant and inter-related mechanisms act in both prokaryotes and eukaryotes to restore DNA integrity following exposures to relatively low doses of sparsely ionizing radiation. Furthermore, the radiation-induced protective mechanisms often overcompensate and minimize the mutagenic potential of the byproducts of normal oxidative metabolism. In contrast to adaptive protection observed at low doses of sparsely ionizing radiation, there is evidence that even a single nuclear traversal by a densely ionizing particle track can trigger harmful effects that spread beyond the traversed cell and induce damaging effects in the nearby bystander cells. In vivo studies examining whether exposure to low dose radiation at younger age modulates the latency of expression of age-related diseases such as cancer, together with studies on the role of genetic susceptibility, will further illuminate the magnitude of risk of exposure to low dose radiation.

Assessment of cytotoxic damage induced by irradiation combined with hyperthermia and Gemcitabine on cultured glioblastoma spheroid cells

Abstract Background Glioblastoma is a highly lethal tumor. There are several methods for the treatment of glioblastoma including surgery/chemotherapy/radiotherapy/radiosurgery or corticosteroids. However none of them could have improved treatment considerably. Therefore this study assessed the cytotoxicity of the combined treatment with Gemcitabine, radiation and hyperthermia on cultured glioblastoma spheroid cells. Material and methods In this study human glioblastoma cell line U87-MG, was cultured as spheroid using the liquid overlay technique. After reaching spheroid dimensions to 100 µm, cells treated by 100 nM Gemcitabine, 2 Gy gamma rays and then hyperthermia of 43 °C for an hour. Colony assay was used to determine cell induced damage and synergistic effect of Gemcitabine, irradiation and hyperthermia. Results The combined therapy indicated greater percentage of cellular damage, although more damages were seen when Gemcitabine, radiation and hyperthermia induced into U87-MG cell line simultaneously. Combination of those three factors in comparison to the radiation combined with hyperthermia and Gemcitabine separately showed 1.85 and 1.5 times more damages respectively. Conclusion This study revealed the synergistic effect for the combined therapy of Gemcitabine, radiation and hyperthermia in glioblastoma treatment.

Swift heavy ion-induced radiation damage in isotropic graphite studied by micro-indentation and in-situ electrical resistivity

Due to its excellent thermo-physical properties and radiation hardness, isotropic graphite is presently the most promising material candidate for new high-power ion accelerators which will provide highest beam intensities and energies. Under these extreme conditions, specific accelerator components including production targets and beam protection modules are facing the risk of degradation due to radiation damage. Ion-beam induced damage effects were tested by irradiating polycrystalline, isotropic graphite samples at the UNILAC (GSI, Darmstadt) with 4.8MeV per nucleon 132Xe, 150Sm, 197Au, and 238U ions applying fluences between 1×1011 and 1×1014ions/cm2. The overall damage accumulation and its dependence on energy loss of the ions were studied by in situ 4-point resistivity measurements. With increasing fluence, the electric resistivity increases due to disordering of the graphitic structure. Irradiated samples were also analyzed off-line by means of micro-indentation in order to characterize mesoscale effects such as beam-induced hardening and stress fields within the specimen. With increasing fluence and energy loss, hardening becomes more pronounced.

Characterization of neutron induced damage effect in several types of metallic multilayer nanocomposites based on Monte Carlo simulation

Metallic multilayer nanocomposites are known to have excellent interface self-healing performance when it comes to repairing irradiation damages, thus showing promise as structural materials for advanced nuclear power systems. The present study investigated the neutron irradiation displacement damage rate, spectra of the primary knocked-on atoms (PKAs) produced in the cascade collision, and the H/He ratio in four kinds of metallic multilayer nanocomposites (Cu/Nb, Ag/V, Fe/W, and Ti/Ta) versus neutrons’ energy. Results suggest that the three neutron induced damage effects in all multilayer systems increased with the increasing of incident neutrons’ energy. For fission reactor environment (1MeV), multilayer’s displacement damage rate is 5–10×1022dpa/(n/cm2) and the mean PKAs energy is about 16keV, without any noteworthy H/He produced. Fe/W multilayer seems very suitable among these four systems. For fusion reactor environment (14MeV), the dominant damage effect varies in different multilayer systems. Fe/W multilayer has the lowest displacement damage under the same neutron flux but its gaseous transmutation production is the highest. Considering the displacement damage and transmutation, the irradiation resistance of Ag/V and Ti/Ta systems seems much greater than those of the other two.

Differential physiological and biochemical responses of two Vigna species under enhanced UV-B radiation

Differential physiological and biochemical responses of two Vigna spp. i.e. Vigna mungo (L.) and Vigna acontifolia (Jacq.) seedlings exposed to enhanced ultraviolet-B (ambient+supplemental, 280–320 nm) radiation were studied. UV-B radiation accelerated the generation of ROS i.e. superoxide radical (O2–), hydrogen peroxide (H2O2) and hydroxyl radical (OH) in leaves, and concomitantly damaging effects on lipid peroxidation, electrolyte leakage and growth in both Vigna spp. were noticed in dose dependent manner, but V. mungo exhibited greater UV-B damaging effects. UV-B stress induced positive response on antioxidants: superoxide dismutase (SOD) and guaiacol peroxidase (GPX) activity, and contents of proline, ascorbic acid, total phenolic contents (TPCs) and total flavonoid contents (TFCs) in leaves of both spp., however, catalase (CAT) exhibited varied activity. The study concludes that substantially higher contents of TPCs and TFCs in epidermal layer, proline and ascorbic acid, and higher CAT activity before and after enhanced UV-B exposure probably attributed greater tolerance to V. acontifolia species, thus exhibited lesser UV-B induced damaging effects on cellular components and growth than that of V. mungo. This study also suggests that V. acontifolia is comparatively resistant to UV-B and thus may be useful for practical cultivation.