The helium bubbles induced by high-energy neutron irradiation can cause intergranular fractures in ferritic/ martensitic steel. To elucidate the susceptibility of different grain boundaries (GBs) to helium-induced embrittlement, molecular dynamics method was applied to study the effect of helium bubbles on the intergranular crack propagation of five representative symmetric tilt grain boundaries (STGBs) in iron, during the tensile processes at 600 K. The GB models with sub-nanometer helium-vacancy (He-V) cluster distributions were derived from equilibrium helium evolution at a helium concentration of 2000 appm. The intergranular crack was inserted in the middle of the GB model to study the orientation effect on crack propagation. The results indicate that in clean GBs, the intergranular crack propagation along lower-energy boundaries exhibit bidirectional ductility, whereas crack propagation along higher-energy boundaries demonstrates unidirectional brittleness. However, He-V clusters can degrade the plastic behavior around the crack tip and promote the propagation of intergranular crack. Crack propagation resistance correlates with GB energy, with the coherent twin boundary Sigma 3{112} showing the highest resistance to crack propagation. These findings elucidate the fundamental mechanism of helium-induced grain boundary embrittlement at the atomic scale and offer insights for mitigating heliuminduced grain boundary embrittlement from the perspective of GB engineering.

The STAR experiment at RHIC at Brookhaven National Laboratory completed the installation of an endcap time-of-flight subsystem in February 2019. The subsystem provided essential mid-rapidity particle identification for the fixed-target portion of phase II of the STAR beam energy scan. The fixed-target program allowed the experiment to access center-of-mass energies from VsNN = 3.0 GeV to VsNN = 7.7 GeV, not accessible by colliding beams. The system's detectors and readout electronics were designed for the CBM experiment at FAIR and adapted for use at STAR. In this paper, we describe the details of the system in terms of geometrical layout, acceptance, calibration, hit reconstruction, and particle identification. The system achieved a time resolution of about 70 ps and a track-matching efficiency of about 70%, meeting the design goals of the project.

To meet the needs of high counting rate and high time resolution in future high energy physics experiments, a prototype of a gas photodetector with a Resistive Plate Chamber (RPC) structure was developed. We simulated the detector's performance using Garfield++ and utilized an ultraviolet laser to evaluate the single photoelectron performance of various mixed gases. The detector uses a low-resistivity (similar to 1.4 x 1010 52 cm) float glass so that its rate capability is significantly higher than that of ordinary float glass (1012-1014 52 cm). The laser test results show that in the MRPC gas mixture (R134a/iC4H10/SF6 (85/10/5)), the best single photoelectron time resolution is 20.3 +/- 1.0 ps at an induced signal charge of 6 x 106 Qe. Increasing the concentration of iC4H10 can effectively reduce the probability of photon feedback, without changing the time resolution and maximum gain. In addition to its application in high-precision time measurement scenarios (e.g. T0 and TOF), the detector can also quantitatively evaluate the single photoelectron performance of various gases and will be utilized for identifying eco-friendly RPC gases.

The reduced-activation ferritic/martensitic (RAFM) steel CLF-1 has been designed as a candidate structural material for nuclear fusion energy reactors. For engineering mechanical design, the effects of temperature on the strain distribution of CLF-1 steel during uniaxial tensile tests were explored within the temperature range from room temperature to 650 °C using uniaxial tensile tests combined with in situ digital image correlation analysis. Strain-concentrated regions alternately distributed ± 45° along the tensile direction could be attributed to the shear stress having the maximum value at ± 45° along the tensile direction and the coordinated deformation of the microstructure. The total strain distribution changed from a normal distribution to a lognormal distribution with increasing deformation owing to the competition between the elastic and plastic strains at all test temperatures. Strain localization has a strong relationship with temperature at the same engineering strain because of the temperature effects on dynamic strain aging (DSA). The stronger the DSA effect, the stronger the strain localization. With increasing temperature, the stronger the strain localization at the same strain, the weaker the plasticity, that is, DSA-induced embrittlement, and the slower the strength decline, that is, DSA-induced hardening.

The Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose neutrino experiment under construction in South China. This paper presents an updated estimate of JUNO's sensitivity to neutrino mass ordering using the reactor antineutrinos emitted from eight nuclear reactor cores in the Taishan and Yangjiang nuclear power plants. This measurement is planned by studying the fine interference pattern caused by quasi-vacuum oscillations in the oscillated antineutrino spectrum at a baseline of 52.5 km and is completely independent of the CP violating phase and neutrino mixing angle theta(23). The sensitivity is obtained through a joint analysis of JUNO and Taishan Antineutrino Observatory (TAO) detectors utilizing the best available knowledge to date about the location and overburden of the JUNO experimental site, local and global nuclear reactors, JUNO and TAO detector responses, expected event rates and spectra of signals and backgrounds, and systematic uncertainties of analysis inputs. We find that a 3 sigma median sensitivity to reject the wrong mass ordering hypothesis can be reached with an exposure of about 6.5 years x 26.6 GW thermal power.

In order to investigate ablation behavior caused by runaway electrons on plasma facing materials (PFMs), the high energy electron irradiation experiment with a pulse duration of 0.6 µ s at room temperature was performed. Specimens of ITER-grade tungsten (W), W-0.5 wt% ZrC alloy (WZC) and potassium-doped tungsten alloy (W–K) were irradiated at different average energy densities. The results indicate that the radial patterns of corrugated and strip-like bulge products on the irradiated specimens’ surfaces are due to the high energy electron pressure. The average void radius, void number density, area and area number density of bulge products on the surface increase with the average energy density in W and W alloys. Second phase particles add more nucleation sites, making void formation and growth easier in W alloys. WZC and W–K have higher average void number density than W. Voids in W alloys, doping of ZrC particles and the fibrous structure of W–K could help enhance heat dissipation and reduce the height of molten layer thickness. Compared to W alloys, W not only has higher area number density and larger area ratio of bulge products on the surface but also exhibits more droplets and larger droplets dimensions. Higher thermal conductivity of W contributes to the higher average molten layer thickness.

Reduced activation ferritic/martensitic (RAFM) steel has been considered a structural material for fusion reactors, where a unique challenge posed by the magnetic fields in such environments could crucially affect material corrosion behavior. This study investigates the corrosion behavior of CLF-1 steel with varying surface roughness in high-temperature steam (HTS) at 400 degrees C over multiple durations up to 300 h and in hightemperature pressurized water (HTPW) at 300 degrees C for 1000 h. The effects of a near-vertical magnetic field (0.28 T and 0.46 T) on corrosion in the HTS environment were also explored. Results show that both surfacetreated for as-received and polished specimens demonstrate similar progressive increases in oxide film thickness and surface O/(Fe+Cr) atomic ratio under both magnetic and non-magnetic conditions. The oxide formation process consisted of six stages in HTS progressing from small particle layers to flocculent oxides, followed by densification, spinel growth, and eventual lamellar oxide structures. A Similar dual-layer oxide film consisted of Fe-rich outer and Cr-rich inner layers with spinel structures formed in HTPW. The application of a vertical magnetic field significantly induces accelerated corrosion kinetics and the thickening of corrosion film. It also accelerates the phase transition from magnetite to hematite and promotes lamellar microstructure formation that could expand interstitial channels, accelerating the inward diffusion of molecules.

Oxide dispersion-strengthened (ODS) steels are among the most promising candidate structural materials for fusion and Generation-IV (Gen-IV) fission reactors, but the ductility of ODS steels is inferior to its strength properties. Therefore, we investigate void nucleation, considered as the first step of ductile damage in metal, using molecular dynamics simulations. Given that the materials are subjected to extremely complex stress states within the reactor, we present the void nucleation process of 1–4 nm Y2O3 nanoclusters in bcc iron during uniaxial, biaxial, and triaxial tensile deformation. We find that the void nucleation process is divided into two stages depending on whether the dislocations are emitted. Void nucleation occurs at smaller strain in biaxial and triaxial tensile deformation in comparation to uniaxial tensile deformation. Increasing the size of clusters results in a smaller strain for void nucleation. The influence of 1 nm clusters on the process of void nucleation is slight, and the void nucleation process of 1 nm cluster cases is similar to that of pure iron. In addition, void nucleation is affected by both stress and strain concentration around the clusters, and the voids grow first in the areas of high stress triaxiality.

The helium-to-vacancy (He/V) ratio plays a crucial role in the helium bubble-induced damage mechanisms caused by neutron irradiation in reduced activation ferritic/martensitic (RAFM) steels, which are main candidate structural materials for fusion reactors. Based on the results of hardening induced by helium bubble in RAFM steel specimens irradiated in the Swiss spallation neutron source, molecular dynamics (MD) simulations were conducted to investigate the interaction between edge dislocation and helium bubble with varying sizes and He/ V ratios. The barrier strength of helium bubbles were calculated based on the dispersed barrier hardening model. From a new perspective, the He/V ratio of helium bubbles in STIP specimens was evaluated through comparing the barrier strength obtained from experimental hardening data and MD simulations. The results showed that the barrier strength of bubbles initially increased slightly as the He/V ratio increased from 0 to 0.8, reached its peak within the He/V ratio range of 0.8 to 1.1, and then decreased rapidly to a very low level. By comparing the simulated and experimental barrier strength, the He/V ratio range of bubbles in RAFM steel specimens was estimated. The He/V ratio of He bubbles in RAFM steel specimens with middle doses is found to be within the high He/V ratio range of 1.2-1.4, whereas those with low doses and a high dose are situated within the He/V ratio range of 0.8-1.1. Furthermore, the He/V ratio of the helium bubbles in RAFM steels was analyzed in conjunction with existing results.

Abstract We explore the decay of bound neutrons in the JUNO liquid scintillator detector into invisible particles (e.g., $$n\rightarrow 3 \nu $$ n → 3 ν or $$nn \rightarrow 2 \nu $$ n n → 2 ν ), which do not produce an observable signal. The invisible decay includes two decay modes: $$ n \rightarrow { inv} $$ n → inv and $$ nn \rightarrow { inv} $$ n n → inv . The invisible decays of s-shell neutrons in $$^{12}\textrm{C}$$ 12 C will leave a highly excited residual nucleus. Subsequently, some de-excitation modes of the excited residual nuclei can produce a time- and space-correlated triple coincidence signal in the JUNO detector. Based on a full Monte Carlo simulation informed with the latest available data, we estimate all backgrounds, including inverse beta decay events of the reactor antineutrino $${\bar{\nu }}_e$$ ν ¯ e , natural radioactivity, cosmogenic isotopes and neutral current interactions of atmospheric neutrinos. Pulse shape discrimination and multivariate analysis techniques are employed to further suppress backgrounds. With two years of exposure, JUNO is expected to give an order of magnitude improvement compared to the current best limits. After 10 years of data taking, the JUNO expected sensitivities at a 90% confidence level are $$\tau /B( n \rightarrow { inv} ) > 5.0 \times 10^{31} \, \textrm{years}$$ τ / B ( n → inv ) > 5.0 × 10 31 years and $$\tau /B( nn \rightarrow { inv} ) > 1.4 \times 10^{32} \, \textrm{years}$$ τ / B ( n n → inv ) > 1.4 × 10 32 years .

The tensile properties of reduced activation ferritic/martensitic (RAFM) steels are significantly influenced by neutron irradiation. Here, a mechanism-based model taking account of the typical ductile damage process of void nucleation, growth, and coalescence was used to study the temperature and irradiation effects. The elastic–plastic response of RAFM steels irradiated up to 20 dpa was investigated by applying the GTN model coupled with different work hardening models. Through a numerical study of tensile curves, the GTN parameters were identified reasonably and satisfying simulation results were obtained. A combination of Swift law and Voce law was used to define the flow behavior of irradiated RAFM steels. The deformation localization could be adjusted effectively via setting the nucleation parameter εn close to the strain where necking occurs. Because εn changed with uniform elongation, εn decreased with the testing temperature and rose with an irradiation temperature above 300 °C. The nucleation parameter fn increased with the testing temperature for RAFM steels before irradiation. For irradiated RAFM steels, fn barely changed when the irradiation temperature was below 300 °C and then it rose at a higher irradiation temperature. Meanwhile, the ultimate strength of the simulated and experimental curves showed good agreement, indicating that this method can be applied to engineering design.

The physics potential of detecting B-8 solar neutrinos will be exploited at the Jiangmen Underground Neutrino Observatory (JUNO), in a model independent manner by using three distinct channels of the charged-current (CC), neutral-current (NC) and elastic scattering (ES) interactions. Due to the largest-ever mass of C-13 nuclei in the liquid-scintillator detectors and the {expected} low background level, B-8 solar neutrinos would be observable in the CC and NC interactions on C-13 for the first time. By virtue of optimized event selections and muon veto strategies, backgrounds from the accidental coincidence, muon-induced isotopes, and external backgrounds can be greatly suppressed. Excellent signal-to-background ratios can be achieved in the CC, NC and ES channels to guarantee the B-8 solar neutrino observation. From the sensitivity studies performed in this work, we show that JUNO, with ten years of data, can reach the {1 sigma} precision levels of 5%, 8% and 20% for the B-8 neutrino flux, sin(2)theta(12), and Delta m(21)(2), respectively. It would be unique and helpful to probe the details of both solar physics and neutrino physics. In addition, when combined with SNO, the world-best precision of 3% is expected for the B-8 neutrino flux measurement.

Ferritic/martensitic(F/M)steel is widely used as a structural material in thermal and nuclear power plants.However,it is susceptible to intergranular damage,which is a critical issue,under service conditions.In this study,to improve the resist-ance to intergranular damage of F/M steel,a thermomechanical process(TMP)was employed to achieve a grain boundary engineering(GBE)microstructure in F/M steel P92.The TMP,including cold-rolling thickness reduction of 6％,9％,and 12％,followed by austenitization at 1323 K for 40 min and tempering at 1053 K for 45 min,was applied to the as-received(AR)P92 steel.The prior austenite grain(PAG)size,prior austenite grain boundary character distribution(GBCD),and connectivity of prior austenite grain boundaries(PAGBs)were investigated.Compared to the AR specimen,the PAG size did not change significantly.The fraction of coincident site lattice boundaries(CSLBs,3 ≤ Σ ≤ 29)and Σ3n boundaries along PAGBs decreased with increasing reduction ratio because the recrystallization fraction increased with increasing reduction ratio.The PAGB connectivity of the 6％deformed specimen slightly deteriorated compared with that of the AR specimen.Moreover,potentiodynamic polarization studies revealed that the intergranular damage resistance of the studied steel could be improved by increasing the fraction of CSLBs along the PAGBs,indicating that the TMP,which involves low deforma-tion,could enhance the intergranular damage resistance.

Bubble generation can significantly degrade the performance of fusion reactor structural materials. In this work, the temperature effects on the initial clustering of helium (He) atoms, the formation of helium-vacancy clusters (HenVm) and the subsequent growth of the clusters into bubbles in bcc iron under different conditions were simulated by molecular dynamics. The results show that He behaviors are primarily dominated by coalescence at temperature range from 400 K to 500 K, which leads to a preference for He to bind together. Conversely, when temperature is higher than 500 K, dissociation become more prominent, causing large He clusters to be hard to form. Under the conditions of increasing He concentration and irradiation dose, the higher the temperature, the higher the density of HenVm clusters at He concentration around 100 appm. However, the temperature dependence reversed at high He concentration. The detailed analysis of formation cases revealed the percentage of nucleation sites for He bubbles at defects during He segregation. In addition, there is no significant difference among the He/V ratio of HenVm clusters formed at vacancies, interstitial dislocation loops (IDLs) and interstitial sites during the cluster growth. However, the He/V ratio of He bubbles growing on edge dislocation (ED) is overall lower than those growing at other formation sites, since the growth of HenVm clusters on ED requires a lower pressure to kick out self-interstitial atoms (SIAs) or SIA clusters. The average He/V ratio of He bubbles in bulk decreases as temperature rises from 400 K to 800 K, while that of He bubbles growing on ED is independent of temperature.

The direct interaction between cascade and helium bubbles during the thermal spike phase plays an important role in the helium bubbles evolution in metals, which was not fully considered by the present long-time simulation methods. To address this issue, in this work we developed a coupling MD-OKMC method to investigate the helium bubble evolution under irradiation cascade in bcc iron. The short-time collision cascade was simulated by the molecular dynamics (MD), and the long-time helium bubble evolution was modeled by the object kinetic Monte Carlo (OKMC). The MD and OKMC simulations were alternated to imitate the gradual increase of both irradiation dose and helium concentration under experiment conditions. The impact of temperature on the helium bubble evolution under irradiation cascade in bcc iron was investigated and the results were compared with the data from neutron irradiation experiment. It's found that the results of the coupling MD-OKMC were consistent with the experiment results, and were better in agreement with the experiment than the traditional OKMC.

To take full advantage from the LHC upgrade to high luminosity in 2029, the ATLAS community has approved an intensive detector upgrade program that includes the construction of an additional trigger layer positioned close to the BI MDT chambers of the muon spectrometer. These chambers are RPC with thin gas gap, thin High Pressure Laminate electrodes coated with graphite on one side, and only use strips orthogonal to the beam-axis to reconstruct the eta and phi coordinates of the detector point where an ionizing particle passes. A detailed description of the construction and validation of these strip panels in China and Italy assembly sites, is presented here.

The helium bubbles induced by 14 MeV neutron irradiation can cause intergranular fractures in reduced activation ferritic martensitic steel, which is a candidate structural material for fusion reactors. In order to elucidate the susceptibility of different grain boundaries (GBs) to helium-induced embrittlement, the tensile fracture processes of 10 types of GBs with and without helium bubbles in body-centered cubic (bcc) iron at the relevant service temperature of 600 K were investigated via molecular dynamics methods. The results indicate that in the absence of helium bubbles, the GBs studied here can be classified into two distinct categories: brittle GBs and ductile GBs. The atomic scale analysis shows that the plastic deformation of ductile GB at high temperatures originates from complex plastic deformation mechanisms, including the Bain/Burgers path phase transition and deformation twinning, in which the Bain path phase transition is the most dominant plastic deformation mechanism. However, the presence of helium bubbles severely inhibits the plastic deformation channels of the GBs, resulting in a significant decrease in elongation at fractures. For bubble-decorated GBs, the ultimate tensile strength increases with the increase in the misorientation angle. Interestingly, the coherent twin boundary ∑3112 was found to maintain relatively high fracture strength and maximum failure strain under the influence of helium bubbles.

We discuss JUNO sensitivity to the annihilation of MeV dark matter in the galactic halo via detecting inverse beta decay reactions of electron anti-neutrinos resulting from the annihilation. We study possible backgrounds to the signature, including the reactor neutrinos, diffuse supernova neutrino background, charged- and neutral-current interactions of atmospheric neutrinos, backgrounds from muon-induced fast neutrons and cosmogenic isotopes. A fiducial volume cut, as well as the pulse shape discrimination and the muon veto are applied to suppress the above backgrounds. It is shown that JUNO sensitivity to the thermally averaged dark matter annihilation rate in 10 years of exposure would be significantly better than the present-day best limit set by Super-Kamiokande and would be comparable to that expected by Hyper-Kamiokande.

The future fixed target high-rate compressed baryonic matter (CBM) experiment is one of the experimental pillars of the Facility for Antiproton and Ion Research (FAIR) located in Darmstadt/Germany. In order to provide an excellent particle identification (PID) of charged hadrons, the CBM-time-of-flight (TOF) group has developed a concept of a 120 m ^2 large TOF wall with a system time resolution below 80 ps based on multi-gap resistive plate chambers (MRPC). Currently, timing MRPC systems are operated with a gas mixture based on tetrafluoroethane (R134a, C _2 H _2 F _4 ) with additions of few vol _6 ) or/and isobutane (i-C _4 H _10 ). Unfortunately, these gas mixtures have a high global warming potential (GWP) in the order of 1500, and therefore, strategies to reduce the environmental impact have to be developed. The various possibilities, including studies on eco-friendly gases, and the considered strategy by the CBM-TOF group will be elaborated in this article.