Minimizing the diffusivity difference between vacancies and interstitials in multi-principal element alloys.

Interstitial atoms usually diffuse much faster than vacancies, which is often the root cause for the ineffective recombination of point defects in metals under irradiation. Here, via ab initio modeling of single-defect diffusion behavior in the equiatomic NiCoCrFe(Pd) alloy, we demonstrate an alloy design strategy that can reduce the diffusivity difference between the two types of point defects. The two diffusivities become almost equal after substituting the NiCoCrFe base alloy with Pd. The underlying mechanism is that Pd, with a much larger atomic size (hence larger compressibility) than the rest of the constituents, not only heightens the activation energy barrier (Ea) for interstitial motion by narrowing the diffusion channels but simultaneously also reduces Ea for vacancies due to less energy penalty required for bond length change between the initial and the saddle states. Our findings have a broad implication that the dynamics of point defects can be manipulated by taking advantage of the atomic size disparity, to facilitate point-defect annihilation that suppresses void formation and swelling, thereby improving radiation tolerance.

DR5 related autophagy can promote apoptosis in gliomas after irradiation.

As a cancer treatment strategy, irradiation therapy is widely used that can cause DNA breakage and increase free radicals, which leads to different types of cell death. Among them, apoptosis and autophagy are the most important and the most studied cell death processes. Although the exploration of the relationship between apoptosis and autophagy has been a major area of focus, still the molecular mechanisms of autophagy on apoptosis remain unclear. Here, we have revealed that apoptosis was enhanced by the death receptor 5 (DR5) pathway, and the effect of autophagy on apoptosis was promoted by DR5 interacting with LC3B as well as Caspase8 in gliomas after irradiation. Interestingly, we observed that the addition of four different autophagy inducers, rapamycin (RAP), CCI779, ABT737 and temozolomide (TMZ), induced the differences of DR5 expression and cell apoptosis after irradiation. Unlike RAP and CCI779, ABT737 and TMZ were able to increase DR5 expression and further induce cell death. Therefore, we have concluded that DR5 plays a novel and indispensable role in promoting cell apoptosis under irradiation and suggest a potential therapeutic approach for glioblastoma treatment.

The Rab GTPase activating protein Gyp2 contributes to UV stress tolerance in Metarhizium acridum.

GTPase activation protein (GAP) for Rab GTPases can accelerate GTP hydrolysis to alter the activity of Rab GTPases. To explore the function of GAP in entomopathogenic fungi, we constructed a deletion mutant of Gyp2 gene, a member of the Gyp (GAP for Ypt/Rab proteins) family in the locust-specific fungal pathogen, Metarhizium acridum. Results showed that the ∆MaGyp2 mutant had dramatically decreased tolerance to ultraviolet irradiation compared to wild type strain. Quantitative real-time PCR revealed that UV irradiation repair related genes Uve1 and WC1 were downregulated in ∆MaGyp2 mutant. Seven of other ten Gyp family members had significantly increased transcription in ∆MaGyp2 mutant compared with wild type, which may partly rescue the deficiency of MaGyp2.

Defect properties of a body-centered cubic equiatomic TiVZrTa high-entropy alloy from atomistic simulations.

TiVZrTa high-entropy alloys (HEAs) have been experimentally proven to exhibit excellent irradiation tolerance. In this work, defect energies and evolution were studied to reveal the underlying mechanisms of the excellent irradiation tolerance in TiVZrTa HEA via molecular statics calculations and molecular dynamics simulations. The atomic size mismatch of TiVZrTa is ∼6%, suggesting a larger lattice distortion compared to most face-centered cubic and body-centered cubic M/HEAs. Compared to pure Ta and V, smaller vacancy formation and migration energies with large energy spreads lead to higher equilibrium vacancy concentration and faster vacancy diffusion via low-energy migration paths. Vacancies in TiVZrTa have weaker abilities to form large vacancy clusters and prefer to form small clusters, indicating excellent resistance to radiation swelling. The formation energies of different types of dumbbells in TiVZrTa show significant differences and have large energy spreads. The binding abilities of interstitials in TiVZrTa are weaker compared to that in pure Ta and V. In TiVZrTa, fast vacancy diffusion and slow interstitial diffusion result in closer mobilities of vacancies and interstitials, significantly promoting point defect recombination. We further studied the effects of short-range ordered structures (SROs) on defect diffusion and evolution. SROs in TiVZrTa can effectively lead to higher fractions of defect recombination and fewer surviving defects. Our findings provide a comprehensive understanding of the underlying mechanisms of the high irradiation tolerance in body-centered cubic HEAs with large lattice distortion and suggest SROs are beneficial microstructures for enhancing irradiation tolerance.

He-ion Irradiation Effects on the Microstructures and Mechanical Properties of the Ti-Zr-Hf-V-Ta Low-Activation High-Entropy Alloys.

High-entropy alloys (HEAs) have shown promising potential applications in advanced reactors due to the outstanding mechanical properties and irradiation tolerance at elevated temperatures. In this work, the novel low-activation Ti2ZrHfxV0.5Ta0.2 HEAs were designed and prepared to explore high-performance HEAs under irradiation. The microstructures and mechanical properties of the Ti2ZrHfxV0.5Ta0.2 HEAs before and after irradiation were investigated. The results showed that the unirradiated Ti2ZrHfxV0.5Ta0.2 HEAs displayed a single-phase BCC structure. The yield strength of the Ti2ZrHfxV0.5Ta0.2 HEAs increased gradually with the increase of Hf content without decreasing the plasticity at room and elevated temperatures. After irradiation, no obvious radiation-induced segregations or precipitations were found in the transmission electron microscope results of the representative Ti2ZrHfV0.5Ta0.2 HEA. The size and number density of the He bubbles in the Ti2ZrHfV0.5Ta0.2 HEA increased with the improvement of fluence at 1023 K. At the fluences of 1 × 1016 and 3 × 1016 ions/cm2, the irradiation hardening fractions of the Ti2ZrHfV0.5Ta0.2 HEA were 17.7% and 34.1%, respectively, which were lower than those of most reported conventional low-activation materials at similar He ion irradiation fluences. The Ti2ZrHfV0.5Ta0.2 HEA showed good comprehensive mechanical properties, structural stability, and irradiation hardening resistance at elevated temperatures, making it a promising structural material candidate for advanced nuclear energy systems.

MoS2 Nanocomposite Films with High Irradiation Tolerance and Self-Adaptive Lubrication.

Although nanostructures and oxide dispersion can reduce radiation-induced damage in materials and enhance radiation tolerance, previous studies prove that MoS2 nanocomposite films subjected to several dpa heavy ion irradiation show significant degradation of tribological properties. Even in YSZ-doped MoS2 nanocomposite films, irradiation leads to obvious disordering and damage such as vacancy accumulation to form lamellar voids in the amorphous matrix, which accelerates the failure of lubrication. However, after thermal annealing in vacuum, YSZ-doped MoS2 nanocomposite films exhibit high irradiation tolerance, and their wear duration remains unchanged and the wear rate was nearly three orders of magnitude lower than that of the as-deposited films after 7 dpa irradiation. This successful combination of anti-irradiation and self-adaptive lubrication mainly results from the manipulation of the nanosize and the change of composition by annealing. Compared with the smaller nanograins in as-deposited MoS2/YSZ nanocomposite films, the thermally annealed MoS2 nanocrystals (7-15 nm) with fewer intrinsic defects exhibited remarkable stabilization upon irradiation. Abundant amorphous nanocrystal phases in ion-irradiated thermally annealed films, where each has advantages of their own, greatly inhibit accumulation of voids and crack growth in irradiation; meanwhile, they can be easily self-assembled under induction of friction and achieve self-adaptive lubrication.

Molecular Characterization and Identification of Calnexin 1 As a Radiation Biomarker from Tradescantia BNL4430.

Calnexin (CNX) is an integral membrane protein that functions as a chaperone in the endoplasmic reticulum for the correct folding of proteins under stress conditions, rendering organisms tolerant under adverse conditions. Studies have investigated the cytogenetic effects of gamma irradiation (Ɣ-IR) on plants, but information on the molecular response under Ɣ-IR remains limited. Previously, we constructed a cDNA library of an irradiation-sensitive bioindicator plant, Tradescantia BNL4430 (T-4430) under Ɣ-IR, in which the Calnexin-1 gene was highly upregulated at 50 mGy treatment. TrCNX1 encodes a 61.4 kDa protein with conserved signature motifs similar to already reported CNX1s. TrCNX1 expression was evaluated by semiquantitative reverse transcriptase PCR and quantitative real-time PCR and was ubiquitously expressed in various tissues and highly upregulated in flower petals under 50 mGy Ɣ-IR stress. The protective function of TrCNX1 was investigated by overexpression of TrCNX1 in an Escherichia coli BL21(DE3) heterologous system. Using plate assay, we showed that TrCNX1 increased the viability of E. coli transformants under both UV-B and Ɣ-IR compared with the control, demonstrating that TrCNX1 functions under irradiation stress. TrCNX1 may enhance irradiation stress tolerance in crops and act as a radio marker gene to monitor the effects of radiation.

Design of radiation tolerant materials via interface engineering.

A novel interface engineering strategy is proposed to simultaneously achieve superior irradiation tolerance, high strength, and high thermal stability in bulk nanolayered composites of a model face-centered-cubic (Cu)/body-centered-cubic (Nb) system. By synthesizing bulk nanolayered Cu-Nb composites containing interfaces with controlled sink efficiencies, a novel material is designed in which nearly all irradiation-induced defects are annihilated.