Increase In Radiation Resistance Research Articles

Radiation resistance of polypropylene modified with nanoparticles of oxide compounds

The results of studies of optical properties in UV, visible and IR spectral regions, and radiation resistance of nanocomposites based on polypropylene modified with nanoparticles of oxide compounds (ZrO2, Al2O3, SiO2, MgO, TiO2, ZnO) are presented. Diffuse reflectance spectra were recorded under 2 ∙ 10−6 torr vacuum before and after electron irradiation (in situ, Е = 30 keV, F = 2 ∙ 1016 cm−2). According to research findings, modification of polypropylene with nanoparticles leads to an increase in radiation resistance, which depends on the structure of the nanopowders, their size and specific surface area. The SiO2 nanopowder, characterized by its amorphous nature, the largest specific surface area, and the smallest particle size, stands as the most effective modifier for enhancing radiation resistance. The IR-Fourier spectra of electron-irradiated samples are similar to the original spectra. A slight decrease in transmission across all characteristic bands compared to the non-irradiated samples indicates minor structural changes as a result of irradiation.

Acquired Radiation Resistance Induces Thiol-dependent Cisplatin Cross-resistance.

Resistance to radiation remains a significant clinical challenge in non-small cell lung carcinoma (NSCLC). It is therefore important to identify the underlying molecular and cellular features that drive acquired resistance. We generated genetically matched NSCLC cell lines to investigate characteristics of acquired resistance. Murine Lewis lung carcinoma (LLC) and human A549 cells acquired an approximate 1.5-2.5-fold increase in radiation resistance as compared to their parental match, which each had unique intrinsic radio-sensitivities. The radiation resistance (RR) was reflected in higher levels of DNA damage and repair marker γH2AX and reduced apoptosis induction after radiation. Morphologically, we found that radiation resistance A549 (A549-RR) cells exhibited a greater nucleus-to-cytosol (N/C) ratio as compared to its parental counterpart. Since the N/C ratio is linked to the differentiation state, we next investigated the epithelial-to-mesenchymal transition (EMT) phenotype and cellular plasticity. We found that A549 cells had a greater radiation-induced plasticity, as measured by E-cadherin, vimentin and double-positive (DP) modulation, as compared to LLC. Additionally, migration was suppressed in A549-RR cells, as compared to A549 cells. Subsequently, we confirmed invivo that the LLC-RR and A549-RR cells are also more resistance to radiation than their isogenic-matched counterpart. Moreover, we found that the acquired radiation resistance also induced resistance to cisplatin, but not carboplatin or oxaliplatin. This cross-resistance was attributed to induced elevation of thiol levels. Gamma-glutamylcysteine synthetase inhibitor buthionine sulfoximine (BSO) sensitized the resistant cells to cisplatin by decreasing the amount of thiols to levels prior to obtaining acquired radiation resistance. By generating radiation-resistance genetically matched NSCLC we were able to identify and overcome cisplatin cross-resistance. This is an important finding arguing for combinatorial treatment regimens including glutathione pathway disruptors in patients with the potential of improving clinical outcomes in the future.

P17.11.A DEVELOPMENT AND CHARACTERISATION OF THE QCELL-R RECURRENT GLIOBLASTOMA PRIMARY CELL LINE RESOURCE: MODELS TO DRIVE BREAKTHROUGH DISCOVERIES IN BRAIN CANCER

Abstract BACKGROUND Glioblastoma (GBM) is the most aggressive brain tumour in adults, with a median survival of only 15 months. Despite aggressive treatment with chemotherapy using temozolomide and radiotherapy, GBM has a high prevalence of recurrence with almost all cases recurring within the first year. This highlights a clear need to develop a deeper understanding of GBM recurrence and to develop effective models to test novel therapies. The vast inter- and intra-tumoural heterogeneity and tumour cell plasticity are complicating the development of effective therapies for brain cancer patients. Large-scale genomic analyses of primary and recurrent human GBM tumour samples have revealed a complex genomic architecture. However, the majority of GBM discovery science has been conducted in treatment naïve tumour models, which fail to capture therapy resistance and tumour evolution. Hence, these changes have been difficult to link to GBM growth and functional cell properties upon recurrence. MATERIAL AND METHODS To address this, we have developed the QCell-R resource, a collection of functional models of recurrent GBM. In collaboration with the Royal Brisbane and Women’s Hospital (RBWH), pair-matched patient tumour samples from the initial resection and at recurrence post-therapy have been collected. From these tissue specimens, in vitro cell lines in both 2D and 3D cultures and in vivo orthotopic xenograft models have been developed. Response to standard of care therapy (temozolomide and radiotherapy) were assessed using IncuCyte proliferation assays. Bulk mRNA, scRNA and exome sequencing were also performed. RESULTS QCell-R consists of 11 patient-derived recurrent GBM models, with the time between resections varying from 5-13 months. There are four pair-matched QCell-R models, as well as three standalone recurrent models. Response to standard of care therapy varied between models, with one model exhibiting a four fold higher growth rate-50 (GR50) after temozolomide treatment and a 2.7 fold increase in radiation resistance compared to the matched treatment naïve counterpart. The mRNA and scRNA sequencing has been compared to publicly available datasets to identify genes of interest that may be targetable in recurrence to test in these models. CONCLUSION QCell-R represents a valuable resource to define novel therapies for recurrent GBM. Elucidation of tumour heterogeneity and tumour evolution will identify targetable genes contributing to therapy resistance in these models. Identifying these targetable genes from QCell-R allows the development of novel treatments, creating strategies that may reduce the rate of recurrence by limiting therapy resistance and inhibiting recurrence-initiating cells.

Abstract 1088: Acquired radiation resistance induces thiol-dependent cisplatin cross-resistance

Abstract Purpose. Resistance to radiation, both intrinsic and acquired, remains a significant clinical challenge. It is therefore import to identify the underlying molecular and cellular features involved in this resistance. Materials and Methods. We generated genetically-matched counterparts of various degrees of radiation sensitivity in non-small cell lung carcinoma (NSCLC) tumor models to define characteristics of acquired resistance through repeated exposures to conventional X-ray radiation. Results. As assessed by cell viability and clonogenic assays murine Lewis lung carcinoma (LLC) and human A549 cell lines acquired an approximate 1.5 - 2-fold increase in radiation resistance (RR) as compared to its parental counterpart. Morphologically, we found that A549-RR exhibited a greater nucleus-to-cytosol (N/C) ratio as compared to its respective counterpart. Since the N/C ratio has been linked to the differentiation state, we next investigated the epithelial-to-mesenchymal transition (EMT) phenotype and cellular plasticity. We found that A549 have a greater radiation-induced plasticity, as measured by E-cadherin, vimentin and double positive (DP) modulation, as compared to LLC. Additionally, migration was suppressed in A549-RR, as compared to A549. Subsequently, we confirmed that the LLC-RR and A549-RR are also more resistant to radiotherapy than their isogenic-matched counterpart in vivo. Remarkably, we found that the acquired radiation resistance also induced resistance to first-line chemotherapeutic cisplatin, but not carboplatin or oxaliplatin. This cross-resistance was attributed to induced elevated thiol levels. Decreasing the amount of thiols with buthionine sulfoximine (BSO), a gamma-glutamylcysteine synthetase inhibitor, sensitized the resistant cells to cisplatin, to levels similar as parental cells. Conclusions. By generating genetically-matched radiation resistant NSCLC tumor models we were able to identify and overcome cisplatin cross-resistance. This is an important finding arguing for multi-modality treatment regimens with the potential of improving clinical outcomes in the future. Citation Format: Samir V. Jenkins, Shruti Shah, Azemat Jamshidi-Parsian, Amir Mortazavi, Gunnar Boysen, Kieng B. Vang, Robert J. Griffin, Narasimhan Rajaram, Ruud P. Dings. Acquired radiation resistance induces thiol-dependent cisplatin cross-resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1088.

Investigation into the communication between unheated and heat-stressed Caenorhabditis elegans via volatile stress signals

Our research group has recently found that radiation-induced airborne stress signals can be used for communication among Caenorhabditis elegans (C. elegans). This paper addresses the question of whether heat stress can also induce the emission of airborne stress signals to alert neighboring C. elegans and elicit their subsequent stress response. Here, we report that heat-stressed C. elegans produces volatile stress signals that trigger an increase in radiation resistance in neighboring unheated C. elegans. When several loss-of-function mutations affecting thermosensory neuron (AFD), heat shock factor-1, HSP-4, and small heat-shock proteins were used to test heat-stressed C. elegans, we found that the production of volatile stress signals was blocked, demonstrating that the heat shock response and ER pathway are involved in controlling the production of volatile stress signals. Our data further indicated that mutations affecting the DNA damage response (DDR) also inhibited the increase in radiation resistance in neighboring unheated C. elegans that might have received volatile stress signals, indicating that the DDR might contribute to radioadaptive responses induction by volatile stress signals. In addition, the regulatory pattern of signal production and action was preliminarily clarified. Together, the results of this study demonstrated that heat-stressed nematodes communicate with unheated nematodes via volatile stress signals.

High-Complexity cellular barcoding and clonal tracing reveals stochastic and deterministic parameters of radiation resistance.

It is elusive whether clonal selection of tumor cells in response to ionizing radiation (IR) is a deterministic or stochastic process. With high resolution clonal barcoding and tracking of over 400 000 HNSCC patient-derived tumor cells the clonal dynamics of tumor cells in response to IR was analyzed. Fractionated IR induced a strong selective pressure for clonal reduction which significantly exceeded uniform clonal survival probabilities indicative for a strong clone-to-clone difference within tumor cell lines. IR induced clonal reduction affected the majority of tumor cells ranging between 96% and 75% and correlated to the degree of radiation sensitivity. Survival to IR is driven by a deterministic clonal selection of a smaller population which commonly survives radiation, while increased clonogenic capacity is a result of clonal competition of cells which have been selected stochastically. A 2-fold increase in radiation resistance results in a 4-fold (P< .05) higher deterministic clonal selection showing that the ratio of these parameters is amenable to radiation sensitivity which correlates to prognostic biomarkers of HNSCC. Evidence for the existence of a rare subpopulation with an intrinsically radiation resistant phenotype commonly surviving IR was found at a frequency of 0.6% to 3.3% (P< .001, FDR 3%). With cellular barcoding we introduce a novel functional heterogeneity associated qualitative readout for tracking dynamics of clonogenic survival in response to radiation. This enables the quantification of intrinsically radiation resistant tumor cells from patient samples and reveals the contribution of stochastic and deterministic clonal selection processes in response to IR.

On improving the radiation resistance of gallium oxide for space applications

A method is proposed for increasing the radiation resistance of semiconductor crystals (AlxGa1-x)2O3, which are promising for creating power electronics and optoelectronic devices for spacecraft performing tasks in near-earth orbits. The effect of the aluminum content on the bandgap in (AlxGa1-x)2O3 single crystals grown from a melt by the Czochralski method is investigated. The necessary conditions for the formation of a high-quality seed and subsequent growth of single crystals are achieved by setting temperature gradients at each successive stage of growth. The results of energy-dispersive X-ray spectroscopy analysis and optical transmission spectra of (AlxGa1-x)2O3 crystals with an aluminum content from 0 to 7.32% are presented. It is shown that an increase in the aluminum content leads to a monotonic increase in the bandgap from 4.7 eV to 5.0 eV, which provides an increase in radiation resistance.

Possibility of using yttrium oxide powder as a strengthening phase for centrifugal casting of corrosion-resistant steels

The authors have made an analysis of necessity to improve the composition of the existing structural materials for critical purposes in the direction of creating metal matrix materials, which combine a highly plastic metal base and refractory high-strength high-modulus fillers. For iron matrix alloys, dispersed yttrium oxide (Y2O3 ) particles are preferred because of their stability at pyrometallurgical process temperatures and inertness to alloy components. The technology of obtaining new materials by introducing dispersed particles into a liquid melt during casting using a centrifugal casting machine to obtain a hollow (pipe) billet is considered. The possibility of increasing the mechanical and operational properties of metal matrix materials in comparison with monomaterial is shown. The article describes results of the thermodynamic modeling of high-temperature processes occurring in the yttrium oxide - metal matrix (melt) system. Modeling was carried out using the FactSage software package. A composition corresponding to 12Cr18Ni10Ti steel was used as the modeling composition of the matrix material. The calculations were made according to the ratio of 1 g of yttrium oxide additive per 100 g of matrix metal melt. From the simulation results it is possible to conclude that the introduced dispersed yttrium oxide powder does not interact with the alloy components, does not dissociate, and does not undergo allotropic transformations. The expediency of conducting experiments on the production of centrifugal castings using yttrium oxide as a hardening phase with the aim of a possible increase in radiation resistance is shown. Directions are indicated for developing the most effective technology for creating metallic materials based on an iron matrix dispersed-hardened by yttrium oxide.

Critical PO2 as a diagnostic biomarker for the effects of low-oxygen modified and controlled atmospheres on phytosanitary irradiation treatments in the cabbage looper Trichoplusia ni (Hübner).

Phytosanitary irradiation is a sustainable alternative to chemical fumigants for disinfesting fresh commodities from insect pests. However, irradiating insects in modified atmospheres with very low oxygen (<1 kPa O2 ) has repeatedly been shown to increase radioprotective response. Thus, there is a concern that modified atmosphere packaging could reduce the efficacy of phytosanitary irradiation. One hurdle slowing the widespread application of phytosanitary irradiation is a lack of knowledge about how moderate levels of hypoxia relevant to the modified atmosphere packaging of most fresh commodities (3-10 kPa O2 ) may affect phytosanitary irradiation treatments. Therefore, we hypothesize that critical PO2 (Pcrit ), the level of oxygen at which an insect's metabolism becomes impaired, can be used as a diagnostic biomarker to predict the induction of a radioprotective response. Using the cabbage looper Trichoplusia ni (Hübner), we show that there is a substantial increase in radiation resistance when larvae are irradiated in atmospheres more hypoxic than their Pcrit (3.3 kPa O2 ). These data are consistent with our hypothesis that Pcrit could be used as a diagnostic biomarker for what levels of hypoxia may induce radioprotective effects that could impact phytosanitary irradiation treatments. We propose that the relationship between Pcrit and radioprotective effects could allow us to build a framework for predicting the effects of low-oxygen atmospheres on the efficacy of phytosanitary irradiation. However, more widespread studies across pest species are still needed to test the generality of this idea.

Analytical formulation for radiation characteristics of a surface wave sustained plasma antenna

This paper reports the analytical formulation of a surface wave sustained plasma antenna based on the antenna theory and the theory for a surface wave sustained plasma. The antenna (tube) structure is a basic quarter-wavelength monopole antenna, comparable to a wavelength of a surface wave. The theory for a surface wave sustained plasma in a semi-infinitely long tube is extended to a finite length plasma. The electron density distribution is calculated based on the extended theory, and antenna characteristics are obtained from the electron density distribution. The analytical results obtained from the formulation show good agreement with the numerical results. The electron density in the finite length tube depends on the existence of the interference between forward- and backward-traveling waves and the boundary condition at the tube end. The electron density distribution is determined based on the balance between the forward- and backward-traveling waves. In the case that the plasma does not reach the tube end, which is equivalent to the case of a semi-infinitely long tube, the antenna gain is constant at a low value due to high plasma resistance and low radiation resistance, without the propagation of the backward-traveling wave. Once the plasma reaches the tube end, due to the coexistence of the forward- and backward-traveling waves with their interference, the electron density is elevated fairly beyond the critical density for sustaining surface wave propagation. Consequently, the antenna gain increases with the synergistic effect of the decrease in plasma resistance and the increase in radiation resistance, and the surface wave sustained plasma works as an antenna.

Swelling of improved 16Cr–15Ni–2Mo–Mn–Ti–V–B steel under dose rates from 1 × 10−8 to 1.7 × 10−6 dpa/s

Radiation-induced swelling negatively affects the operability of structural units of fast breeder reactor (FBR) cores. Therefore, search for new and improvement of existing steels for reducing swelling is an important task.Since 2003, type 16Cr–15Ni–2Mo–Mn–Ti–V–B steel has shown a significant increase in radiation resistance due to its improved composition and heat treatment. Specialists of the JSC INM studied swelling of 16Cr–15Ni–2Mo–Mn–Ti–V–B steel with improved composition, data on the maximum swelling temperature, average swelling rate within typical coolant temperature ranges, as well as fast reactor dose rate were obtained.The obtained results are based on swelling measurements using hydrostatic weighing and transmission microscopy. Errors in hydrostatic measurements were examined with involvement of metallography data and selection of immersion liquid.It was revealed that the average swelling rate of improved 16Cr–15Ni–2Mo–Mn–Ti–V–B steel at the maximum swelling temperature is within the range of 0.04–0.14%/dpa. Shifting of this temperature from 460 to 520°C with increase of the maximum damaging dose from 60 to 80dpa (1.3× 10−6 and 1.7×10−6dpa/s, respectively), is observed. At doses below 10dpa and temperatures below 400°C the average swelling rate may reach 0.04%/dpa. At temperatures of about 600°C and irradiation doses below 50dpa the swelling rate does not exceed 0.01%/dpa during the whole period of observation.

Hemopoietic Progenitor Cells from the Bone Marrow of Serpinb3A-/- Mice Are Radioresistant

Introduction: Serpins are a superfamily of serine proteases that regulate proteolytic pathways by utilizing a conformational change to bind to and inhibit multiple peptidases. Currently 36 human serpins have been identified, but the roles of most are not fully understood (Silverman et al., J Biol Chem. 285(32):24299-305, 2010). A majority of serpins inhibit serine proteases but serpins that inhibit lysosomal cytosine peptidases, granzymes, serine protease and calpains. Previous studies have shown that serpins play a critical role in cell survival by blocking lysosomal induced necrosis injury. Serpinb3A (Antichymotrypsin) has been identified as an inhibitor of the serine peptidases, chymotrypsin and cathepsin G. We now report that hematopoietic progenitor cells in the bone marrow of Serpinb3A-/- mice are radioresistant.Materials & Methods: Serpinb3A-/- and control Balb/c mice were obtained from Charles River and were housed five per cage according to University of Pittsburgh Institutional Animal Care and Use Committee (IACUC) regulations. All protocols were approved by the University of Pittsburgh IACUC. Veterinary care was provided by the Division of Laboratory Animal Research of the University of Pittsburgh. Whole bone marrow was obtained by flushing the marrow from the femurs of sacrificed Serpinb3A-/- and Balb/c mice. Single cell suspensions were irradiated to doses ranging from 0 to 8 Gy using a at 70 cGy/min using a Shepherd Mark 1 137Cs γ-ray source (J.L. Shepherd, San Fernando, CA, USA). The cells were plated in 0.8% methylcellulose containing hematopoietic growth supportive medium (StemCell Technology product #3134) at varying densities in quadruplicate in Linbro plates (Fisher Scientific, Pittsburgh, PA, USA) and incubated at 37°C and 5% CO2 for 9-11 days at which time the number of colony forming unit granulocyte-macrophage (CFU-GM) colonies of 50 cells or greater were counted. The data from 5 experiments was analyzed using linear quadratic and single-hit, multi-target models.Results: CFU-GM from Serpinb3A-/- mouse marrow showed an increase in radiation resistance with an increase in the shoulder of the irradiation survival curve compared to Balb/c marrow (ň = 4.9 ± 1.4 and 1.4 ± 0.1, p = 0.0451, respectively). There was no significant difference in the Do for CFU-GM of the two mouse strains (Do = 1.48 ± 0.19 Gy for Serapinb3A-/- mice and 1.56 ± 0.06 Gy for Balb/c mice, p = 0.0997.Conclusions: The data support a possible role for the loss of Serpinb3a in providing a cell survival advantage for hematopoietic progenitor cells exposed to lethal doses of ionizing irradiation. This would suggest that the Serpinb3a target protease helps repair the cellular injury induced by ionizing radiation. Alternatively, the germ line loss of Serpinb3a may up-regulate the expression of other clade B serpins known to protect cells from injury. Ongoing studies will help determine the nature of this protective effect against radiation-induced cell death. DisclosuresNo relevant conflicts of interest to declare.

Deformation behavior features of composite of polystyrene with cesium sulfate filler during ultraviolet and X-ray irradiation

A noticeable increase in radiation resistance of polystyrene upon the addition of cesium sulfate particles is found. This is due to the fact that the fragments of polystyrene molecules fixed by filler particles do not diverge at radiation breakage of interatomic bonds, keeping a high possibility of recovery thereof. When studying X-ray luminescence of this composite, it is found that its deformation results in the decrease in the proportion of luminescence of organic luminophores, which indicates direct involvement of contact areas between the particles and molecules in the transfer of energy of electronic excitations according to the Dexter or Frerichs mechanism.

MTR-03ATRX REDUCTION PROMOTES ALKYLATING AGENT RESISTANCE AND XENOGRAFT GROWTH IN A SUBSET OF GLIOMAS

MTR-03. ATRX REDUCTION PROMOTES ALKYLATING AGENT RESISTANCE AND XENOGRAFT GROWTH IN A SUBSET OF GLIOMAS Ming Yuan, Ping An, Kah Suan Lim, Isabella Taylor, Fausto Rodriguez, Eric Raabe, and Charles Eberhart; Johns Hopkins University, Baltimore, MD, USA BACKGROUND:Loss ofATRXfunctionhas been implicated inalternative lengthening of telomeres (ALT) and is common in IDH mutant astrocytoma of varying grades. However, the functional effects of ATRX loss on glioma growth are not clear, although it has been suggested that it can modulate response to ATR inhibitors such as VE-821. METHODS: We evaluated the ALT-positive GBM neurosphere line JHH-GBM14, which retains ATRX expression in a subset of cells, the ALT-negative neurosphere line 040821 and LN229 cells. Two distinct shRNA were used to suppress ATRX protein expression. RESULTS: ATRX knockdown had no effect on the overall in vitro growth of the three lines, but GBM14 cells became resistant to temozolamide and hydroxyurea after ATRX knockdown, while the two ALT-negative lines did not. A modest, non-significant increase in radiation resistance was also noted. Sensitivity to the ATR inhibitor VE-821 was not affected by decreased ATRX levels in any of the three lines. Interestingly, clonogenic growth of GBM14, theexpression of several stemcellmarkers, aswellas its ability togenerate large flank and intracranial xenografts was increased by ATRX knockdown, while these effects were not seen in 040821 GBM neurospheres. CONCLUSIONS: While ATRX knockdown had little effect on in vitro tumor growth, it dramatically affected the treatment response, clonogenicity and in vivo growth of ALT-positive GBM14 cells, but not two GBM models lacking ALT. These data suggest that in some GBM, ATRX can modulate growth and treatment sensitivity as well as affecting telomere biology. Neuro-Oncology 17:v124–v129, 2015. doi:10.1093/neuonc/nov219.3 Published by Oxford University Press on behalf of the Society for Neuro-Oncology 2015.

Enhanced Radiation Resistance of Methanosarcina soligelidi SMA-21, a New Methanogenic Archaeon Isolated from a Siberian Permafrost-Affected Soil in Direct Comparison to Methanosarcina barkeri.

Permafrost-affected soils are characterized by a high abundance and diversity of methanogenic communities, which are considered suitable model organisms for potential life on Mars. Methanogens from Siberian permafrost have been proven to be highly resistant against divers stress conditions such as subzero temperatures, desiccation, and simulated thermophysical martian conditions. Here, we studied the radiation resistance of the currently described new species Methanosarcina soligelidi SMA-21, which was isolated from a Siberian permafrost-affected soil, in comparison to Methanosarcina barkeri, which is used as a reference organism from a nonpermafrost soil environment. Both strains were exposed to solar UV and ionizing radiation to assess their limits of survival. Methanosarcina soligelidi exhibit an increase in radiation resistance to UV (2.5- to 13.8-fold) and ionizing radiation (46.6-fold) compared to M. barkeri. The F10 (UVC) and D10 (X-rays) values of M. soligelidi are comparable to values for the well-known, highly radioresistant species Deinococcus radiodurans. In contrast, the radiation response of M. barkeri was highly sensitive to UV and ionizing radiation comparably to Escherichia coli and other radiosensitive microorganisms. This study showed that species of the same genus respond differently to UV and ionizing radiation, which might reflect the adaptation of Methanosarcina soligelidi SMA-21 to the harsh environmental conditions of the permafrost habitat. Methanogenic archaea-Environmental UV-Ionizing radiation-Permafrost-Radiation resistance-Mars.

Experimental and ab initio study of enhanced resistance to amorphization of nanocrystalline silicon carbide under electron irradiation

The crystalline-to-amorphous transition in nanocrystalline silicon carbide (ncSiC) has been studied using 1.25MeV electron irradiation. When compared to literature values for single crystal silicon carbide under electron irradiation, an increase in the dose to amorphization (DTA) was observed, indicative of an increase in radiation resistance. Factors that contribute to this improvement are grain refinement, grain texture, and a high density of stacking faults (SFs) in this sample of ncSiC. To test the effect of SFs on the DTA, density functional theory simulations were conducted. It was found that SFs reduced the energy barriers for both Si interstitial migration and the rate-limiting defect recovery reaction, which may explain the increased DTA.

Nanoscale engineering of radiation tolerant silicon carbide

Radiation tolerance is determined by how effectively the microstructure can remove point defects produced by irradiation. Engineered nanocrystalline SiC with a high-density of stacking faults (SFs) has significantly enhanced recombination of interstitials and vacancies, leading to self-healing of irradiation-induced defects. While single crystal SiC readily undergoes an irradiation-induced crystalline to amorphous transformation at room temperature, the nano-engineered SiC with a high-density of SFs exhibits more than an order of magnitude increase in radiation resistance. Molecular dynamics simulations of collision cascades show that the nano-layered SFs lead to enhanced mobility of interstitial Si atoms. The remarkable radiation resistance in the nano-engineered SiC is attributed to the high-density of SFs within nano-sized grain structures that significantly enhance point defect annihilation.

Mutation in the cspH-cspG gene cluster enhances expression of heat-shock proteins and SOS repair system of Escherichia coli

The recessive radioresistance allele gam12 cloned in plasmid pBC4042-gam12 slightly increases the radiation resistance of Escherichia coli wild-type cells. Meanwhile, irradiation by gamma-rays induces transition of r12 mutation to the homozygous state and causes a 3.37-fold increase in radiation resistance of these cells. The mutation gamr12 was located at 22.68 min of the chromosomal map in the region of cspH-cspG gene cluster of cold-shock proteins. Sequence analysis of gam12 allele revealed the nucleotide sequence of cold-shock gene cspG and insertions in the C-terminal part of the gene. Translation of mutant cspG gene can lead to synthesis of a truncated product that represents the N-terminal protein fragment with motifs governing binding with DNA and RNA. Analysis of the Escherichia coli genome revealed motifs recognized by proteins of the cspA family in genes of cold shock, heat shock, SOS regulon, and other systems. These data suggest the possibility of involvement of mutant RNA-chaperones of type CspA' and CspG' in the expression of key genes in systems of SOS repair and recombination or auxiliary stress systems, including heat-shock proteins, in radiation resistant mutants of E. coli.

Operator-constitutive mutation in the recA gene enhances radiation resistance of Escherichia coli

Plasmid pUC19-recAoc carrying a mutant allele of the recA gene, which plays the key role in the control of the SOS repair system and homologous recombinational repair, causes a 1.5-fold increase in radiation resistance of Escherichia coli DeltarecA cells, as compared to the wild-type recA+ cells. The protective effect of this plasmid is drastically reduced in mutant lexA3 recADelta21 deficient in the LexA protein and in induction of the SOS regulon. Plasmid pUC19-recAoc effectively suppresses UV sensitivity of the DeltarecA mutant. Mutation recAo20 allows constitutive high-level synthesis of the RecA protein. This mutation impairs the SOS box in the operator site of the recA gene and enhances heterology of the dimer LexA binding site. These data confirm that high level of the RecA protein synthesis per se is not sufficient for the expression of gamma-inducible functions and that the derepression of lexA-dependent genes, other than recA gene, is necessary for the complete induction of the SOS repair system.

Luminescent protection against radiation damage in wide-gap materials

In the wide-gap metal oxides, with E g lower than the formation energy of a pair of Frenkel defects, hot recombination of nonrelaxed electrons and holes cause the creation of defects under the conditions of high-density excitation. Novel manifestations of the fast direct energy transfer by hot electrons to impurity centers (e.g., in Al 2O 3:Sc 3+ and Al 2O 3:Gd 3+) or to intrinsic defects (F and F + centers induced by the previous irradiation of Al 2O 3 with swift heavy ions) have been revealed using the methods of low-temperature cathodo- and photoluminescence. The contribution of the solid-state analogue of the Franck–Hertz effect as well as of the multiplication processes of electronic excitations to the suppression of hot recombination and the increase of radiation resistance of dielectrics has been analysed.