Spallation Process Research Articles

Au-Doped Black Silicon Photodetector Fabricated by a Femtosecond Laser with Excellent Near-Infrared Response.

Silicon photonic devices are key components in optical imaging and sensing for communication, and the development of silicon-based photodetectors with ideal performance in the visible and infrared spectral ranges can promote the application of silicon photonics in various photoelectronic systems. Here, a Au-doped black silicon photodetector was prepared by a femtosecond laser direct writing technique. The conical micro-/nanostructures with different sizes were produced by different laser fluence irradiation. Ultrafast pump-probe technology revealed that the strong spallation process and phase explosion between Au and silicon facilitate the interfusion of Au atoms into the silicon lattice. EDS analyses, Raman spectra, and XPS spectra show the uniform distribution of Au elements, multiconfiguration amorphous phase transition, and stable chemical valence states of Au elements in Au-doped black silicon layers, respectively. The excellent geometric light trapping performance of the surface conic structure-assisted photodetector achieved a high absorptance of 95% in the 200-1100 nm band. Simultaneously, the introduction of the intermediate band by Au hyperdoping also leads to a strong absorptance of 75% in the 1100-2500 nm band. The photoelectrical response rate of the Au-doped black silicon photodetectors increased by 10 times in the infrared wavelength band by means of the introduced intermediate energy levels through Au element doping. The switching photocurrent ratio is also found to be boosted 10 times, which comes from the reduction of the photon injection barrier. The excellent photoelectronic properties lead to the increased potential of femtosecond laser processing for integration with photonics and electronics, which shows great possibilities in the further progress of energy devices, information technology, and artificial intelligence.

Monte Carlo Simulation of Radioactive Elements Production in Tissues by Spallation in Cancer Therapy

Purpose: High-energy heavy ions generated by accelerators utilized in industrial and medical uses. Ar, C, and He heavy ions have been used in the treatment of cancer. In this research, it was tried to calculate the radioactive elements production in healthy tissues around tumors by heavy ions spallation process in the direct usage of high-energy ions for the treatment of cancerous tumors. Materials and Methods: The radioactive elements production in body tissues irradiated with heavy ions was calculated by Monte Carlo N Particle X-version (MCNPX) code based on the Monte Carlo method. The F8 tally card with FT8 command was utilized to derive the activation and spallation data in the range of Z1 to Z2 atomic numbers. Results: A wide range of radioactive elements was created in healthful tissues in Ne, C, Ar, and He heavy ions therapy. Results show that 10Be,14C, 26Al, 36Cl, 39Ar, 40K, 39Ar, 32Si, 22Na, and 36Cl radioactive materials were produced for high-energy heavy ions spallation in healthy soft tissue. Conclusion: The results of this research show that due to using directly high-energy ions to treat internal tumors, healthy soft tissue is activated. Also, by irradiated Ne, C, Ar, and He ions, the radioactive elements are produced with high gains and long half-lives. Therefore, in the therapy of cancerous tumors with high-energy ions, due to the production of radioactive agents, healthy tissues are at high risk.

Crustal origin for olivine in the lunar Shioli crater ejecta boulders: Insights from the geological setting of Theophilus crater and Nectaris basin

On the Moon, impact craters and basins expose a wide range of crustal and mantle rocks that provide excellent opportunity for sampling them, understanding their origins and reconstructing spatial and temporal evolution of lunar interior. The previous studies detected olivine-bearing mantle rocks in and around large impact craters and basins. The Japanese SLIM mission landed on the ejecta of a ∼ 280-m-diameter Shioli crater that was emplaced on the ejecta blanket of ∼ 103-km-diameter Theophilus crater, for characterizing potential mantle-derived olivine in the Shioli crater ejecta boulders. To test this hypothesis, we studied the geological setting of Shioli crater, host Theophilus crater and Nectaris multi-ring basin using the orbiter data from Chandrayaan-1 and 2, Lunar Reconnaissance Orbiter, and Kaguya missions and the earth-based Arecibo radar observation. The asymmetrically distributed secondary craters and impact melt ponds around Theophilus crater suggests that a northeast-directed oblique impact produced this crater. Composition of Theophilus crater and surrounding region indicates that the crater excavated a heterogeneous target composed of a thin layer of high-Al olivine basalt (Mare Nectaris) underlain by anorthositic highland rocks possibly intruded by Mg-suite plutons; layers of Cyrillus crater ejecta blanket and Nectaris basin materials (both ejecta and impact melt sheets) were also present beneath the mare basalt flows. Hence, the Theophilus ejecta blanket is a mixture of all these materials. Our dating of Theophilus crater suggests that it is a ∼ 2 Ga Eratosthenian crater. Shioli is a fresh simple crater that was formed at ∼ 1 Ma on the uprange ejecta blanket of Theophilus, where the Arecibo radar data indicated the presence of abundant buried Theophilus ejecta boulders. An ESE-directed hypervelocity oblique impact event produced the elongated Shioli crater and its asymmetrically distributed bright ejecta. Shioli is a primary impact crater indicating the role of impact spallation processes associated with this hyper-velocity impact in producing thousands of ejecta (or spall) boulders around Shioli crater, displaying their asymmetric dispersal pattern and spatial variation of boulder sizes and shapes. The larger and elongated boulders are concentrated near the crater rim, while their size and axial ratio gradually decreases outward from the crater rim. The SLIM mission landed on a thin downrange ejecta of Shioli crater, where fewer large-size boulders are present. Our compositional study suggests that the Shioli ejecta boulders are composed of olivine basalt (Mare Nectaris) mixed with highland anorthositic fragments, including the reworked Cyrillus ejecta and Nectaris basin materials. The Shioli ejecta boulders were produced by complex impact fragmentation of already existing, buried Theophilus ejecta boulders. The regional crustal structure of Nectaris basin and its petrological composition suggest that both Nectaris basin and Theophilus crater did not excavate the lunar mantle. Therefore, the Shioli ejecta boulders are of crustal origin, including the olivine minerals present in them. Our results have important implications for the origin of olivine in the Shioli crater boulders being investigated by the SLIM mission.

Aerothermal Loads on a Representative Porous Mesostructure at Flight Conditions Using Direct Simulation Monte Carlo

Spacecraft require thermal protection systems (TPS) in order to survive the extreme conditions present during atmospheric entry missions. Porous ablators are a class of TPS materials that have been used successfully on several entry missions, although they can be difficult to model because of their complex nature at the micro- and mesoscales. Specifically, the processes that lead to mechanical erosion (spallation) of these materials are poorly understood. In order to gain insight into the spallation process, the current work computes aerothermal loads on a mesostructure representative of FiberForm (the substrate of phenolic impregnated carbon ablator) by leveraging a simulation framework involving loosely coupled Computational Fluid Dynamics-Direct Simulation Monte Carlo (CFD-DSMC) simulations of hypersonic boundary layers. CFD boundary layers are extracted from two altitudes, 68.9 and 81 km, along the Stardust entry trajectory and are imposed as boundary conditions on a DSMC simulation over an artificially generated mesostructure, which is representative of the charred layer of the TPS material. In order to produce high-quality results, the DSMC boundary conditions require careful consideration; specifically, Chapman–Enskog distributions are needed to account for large velocity and temperature gradients. Visualizations of the DSMC flowfield indicate excellent agreement with the original CFD data, and the aerothermal loads (heat flux and traction force) on the surface were examined using probability density functions. Additionally, the effects of pyrolysis blowing through the mesostructure on the surface properties are also determined.

Molecular dynamics simulation of spall behavior of amorphous/crystalline composites under shock loading

The industrial application of metallic glass (MG) is greatly limited due to its poor ductility and susceptibility to catastrophic fracture. The mechanical properties of MG can be effectively improved by adding crystal phases to make amorphous/crystalline composites. Meanwhile, spallation is a typical form of dynamic failure of materials under shock loading. However, the spall behavior of amorphous /crystalline composites has been rarely studied. In this work, the shock induced spallation process of Cu50Zr50/copper (Cu) composite materials was investigated through molecular dynamics (MD) simulations. It is found that stress waves transmit and reflect at interface due to the mismatch of acoustic impedance. Besides, MG is “softer” than the single crystal Cu from the perspective of stress wave propagation. By changing the loading direction, it was found that classical spall is more likely to occur in the Cu phase, while micro-spall is more likely to occur in the MG phase. However, as the loading velocity increases, the spall form in the Cu phase will also transform into micro-spall. The spall strength and strain rate through acoustic approximation and MD simulations were also obtained. Finally, it was observed that the tensile stress superposition region caused by interface reflection waves may form new danger points where spallation may initiate, thereby resulting in complex spall phenomena in composite materials. The conclusions obtained reveal the characteristics of the spall phenomenon in Cu50Zr50/Cu composite materials, which is beneficial to further understanding the spall mechanism and providing guidance for designing amorphous/crystalline composite materials under shock loading.

Neutron diffraction: a primer

Abstract Because of the neutron’s special properties, neutron diffraction may be considered one of the most powerful techniques for structure determination of crystalline and related matter. Neutrons can be released from nuclear fission, from spallation processes, and also from low-energy nuclear reactions, and they can then be used in powder, time-of-flight, texture, single crystal, and other techniques, all of which are perfectly suited to clarify crystal and magnetic structures. With high neutron flux and sufficient brilliance, neutron diffraction also excels for diffuse scattering, for in situ and operando studies as well as for high-pressure experiments of today’s materials. For these, the wave-like neutron’s infinite advantage (isotope specific, magnetic) is crucial to answering important scientific questions, for example, on the structure and dynamics of light atoms in energy conversion and storage materials, magnetic matter, or protein structures. In this primer, we summarize the current state of neutron diffraction (and how it came to be), but also look at recent advances and new ideas, e.g., the design of new instruments, and what follows from that.

Lunar Surface Resource Exploration: Tracing Lithium, 7 Li and Black Ice Using Spectral Libraries and Apollo Mission Samples

This is an exercise to explore the concentration of lithium, lithium-7 isotope and the possible presence of black dirty ice on the lunar surface using spectral data obtained from the Clementine mission. The main interest in tracing the lithium and presence of dark ice on the lunar surface is closely related to future human settlement missions on the moon. We investigate the distribution of lithium and 7 Li isotope on the lunar surface by employing spectral data from the Clementine images. We utilized visible (VIS–NIR) imagery at wavelengths of 450, 750, 900, 950 and 1000 nm, along with near-infrared (NIR–SWIR) at 1100, 1250, 1500, 2000, 2600 and 2780 nm, encompassing 11 bands in total. This dataset offers a comprehensive coverage of about 80% of the lunar surface, with resolutions ranging from 100 to 500 m, spanning latitudes from 80°S to 80°N. In order to extract quantitative abundance of lithium, ground-truth sites were used to calibrate the Clementine images. Samples (specifically, 12045, 15058, 15475, 15555, 62255, 70035, 74220 and 75075) returned from Apollo missions 12, 15, 16 and 17 have been correlated to the Clementine VIS–NIR bands and five spectral ratios. The five spectral ratios calculated synthesize the main spectral features of sample spectra that were grouped by their lithium and 7 Li content using Principal Component Analysis. The ratios spectrally characterize substrates of anorthosite, silica-rich basalts, olivine-rich basalts, high-Ti mare basalts and Orange and Glasses soils. Our findings reveal a strong linear correlation between the spectral parameters and the lithium content in the eight Apollo samples. With the values of the 11 Clementine bands and the 5 spectral ratios, we performed linear regression models to estimate the concentration of lithium and 7 Li. Also, we calculated Digital Terrain Models (Altitude, Slope, Aspect, DirectInsolation and WindExposition) from LOLA-DTM to discover relations between relief and spatial distribution of the extended models of lithium and 7 Li. The analysis was conducted in a mask polygon around the Apollo 15 landing site. This analysis seeks to uncover potential 7 Li enrichment through spallation processes, influenced by varying exposure to solar wind. To explore the possibility of finding ice mixed with regolith (often referred to as `black ice’), we extended results to the entire Clementine coverage spectral indices, calculated with a library (350–2500 nm) of ice samples contaminated with various concentrations of volcanic particles.

Thermal spallation of dry rocks induced by flame parallel or normal to layering: Effect of anisotropy

Thermal spallation drilling is a prospective technique in many strategic projects involving energy. To investigate the effect of rock anisotropy on thermal spallation and provide reference for thermal rock-drilling methods, we conducted flame jet experiments on dry shale samples and finite element modelling. Thermal spallation is produced by the growth of pre-existed cracks under compressive thermal stress. These cracks separate thin layers from the bulk of the rock; the layers buckle under compressive stress producing the spalls. Simultaneously, tensile fractures are formed that can inhibit the thermal spallation process. Rock anisotropy can change the thermal spallation zone making it larger (over seven times) or smaller compared to the isotropic case, or even exclude spallation. Comparison with experimentally observed spallation zone in shale samples with different bedding orientations suggests that bedding planes do not induce anisotropy sufficient to affect thermal spallation. Strong anisotropy of rocks can generate thermal tensile fractures directly from the heating surface, the situation impossible in isotropic rocks. During progressive thermal spallation rock anisotropy can make the spallation zone larger or remain unchanged. The results can help understanding thermal spallation of rocks and are instrumental in designing thermal spallation-based drilling technique for strongly anisotropic rocks.

The Shock-Induced Deformation and Spallation Failure of Bicrystal Copper with a Nanoscale Helium Bubble via Molecular Dynamics Simulations.

Both the nanoscale helium (He) bubble and grain boundaries (GBs) play important roles in the dynamic mechanical behavior of irradiated nanocrystalline materials. Using molecular dynamics simulations, we study the shock-induced deformation and spallation failure of bicrystal copper with a nanoscale He bubble. Two extreme loading directions (perpendicular or parallel to the GB plane) and various impact velocities (0.5-2.5 km/s) are considered. Our results reveal that the He bubble shows hindrance to the propagation of shock waves at lower impact velocities but will accelerate shock wave propagation at higher impact velocities due to the local compression wave generated by the collapse of the He bubble. The parallel loading direction is found to have a greater effect on He bubble deformation during shock compression. The He bubble will slightly reduce the spall strength of the material at lower impact velocities but has a limited effect on the spallation process, which is dominated by the evolution of the GB. At lower impact velocities, the mechanism of spall damage is dominated by the cleavage fracture along the GB plane for the perpendicular loading condition but dominated by the He bubble expansion and void growth for the parallel loading condition. At higher impact velocities, micro-spallation occurs for both loading conditions, and the effects of GBs and He bubbles can be ignored.

MCNP simulations for the n_TOF NEAR station

The NEAR station is the newest experimental area of the n_TOF facility at CERN, utilizing the spallation process to generate extremely high neutron flux within a broad energy spectrum. As part of the campaign for the determination of the neutron beam spectral features, numerous foils have been irradiated last year and the induced activities were measured implementing a HPGe detector.
 Experimental data analysis of the irradiated foil’s gamma-ray spectra, yielded the saturated activities for each material that can be used to unfold the characteristics of the neutron flux through data deconvolution using the SAND-II code. Since this process is mostly mathematical and does not account for geometry, shielding and scattering effects, correction factors need to be defined and applied to the measured activities in order to produce a more robust and accurate result.
 For this purpose Monte Carlo simulations using the MCNP code were performed to investigate the self-shielding of the foils and its effect on both the neutron flux and the gamma rays emitted. Also, a detailed simulation including the full geometry of the experimental setup was developed and used in order to investigate possible influence of the peripheral materials (cement, other foils, mylar as well as the aluminum sample holder and rails) to the total flux that reaches each individual foil through scattering of neutrons.

Molecular dynamics investigation of loading orientation effect on dynamic behaviors of void in aluminum

The micro-damage mechanisms in ductile metals play a very important role in the spallation process. Nonequilibrium molecular dynamics (NEMD) is used to examine the effect of loading orientation on void evolution in single crystal (SC) and nanocrystalline (NC) aluminum under isotropic tensions. Besides void nucleation, growth, and coalescence, a brand-new phenomenon, void collapse, is also discovered in the late growth stage, and the collapse behavior is confirmed by the atomic trajectory tracing approach (ATTA). The loading orientation has a significant impact on the maximum void number, maximum void surface area, and void collapse velocity in the SC model but not in the NC model; while the void volume and its fraction that can capture the void collapse behavior are unaffected by the loading direction in the SC and NC models. In the SC model, the loading orientations [−110][001][110] and [100][010][001] make void collapse hardest and simplest. Meanwhile, with the help of the slicing method, it is discovered that the damage mechanism in the NC model is dominated by intracrystalline, intercrystalline, and transcrystalline fractures, with the second being the directional fracture along the grain boundary, whereas it belongs to the intracrystalline fracture in the SC model. In addition, the material experiences the hardening and softening phases during the nucleation stage, which are distinguished by the maximal tensile stress.

Decay heat in ISIS spallation target: simulations and measurements

Spallation targets for neutron production with high energy protons are made of high density and high atomic number materials in order to maximise the yield of neutrons for all the instruments around. Operating a proton beam onto a spallation target produces residual radioactive nuclei either as direct product of the spallation process and as secondary low energy neutron absorption. A reliable estimation of the overall activation and decay heat, as a function of the cooling time and irradiation profile history, is fundamental for a valuable design of the radiation shielding and cooling system during the operation phase as well for envisaging the optimal storage solution at the end of life of the target. This work presents the comparison between the FLUKA predictions of the decay heat in the ISIS TS1 target operated between 2014 and 2019 and the decay heat estimations derived from the measurement of the temperature in each plate at different cooling times. The agreement between the FLUKA predictions and the experimentally assessed values shows and quantifies the goodness of the FLUKA model in predicting measurable physical quantities relevant for the engineering thermal design of the target/reflector and moderator (TRAM) assembly. In addition, it also provides an indirect evidence of the accuracy of the simulated spallation physics and neutron transport throughout the TRAM assembly. Finally this work attempts to highlight and propose a general empirical procedure that could be eventually applied and used to proficiently measure the decay heat at whatever cooling time in targets with similar ISIS design.

Cryogenic hydrogen Moderator infrastructure at ESS

The European Spallation Source (ESS) in Lund, Sweden, is designed to become the most powerful spallation neutron source in the world. As one subsystem of the Target Station, which was developed and built at Central Institute of Engineering, Electronics and Analytics – Engineering and Technology (ZEA-1) of Forschungszentrum Juelich, the cold Moderator slows down high-energy neutrons from the spallation process. To gain maximum neutron flux intensities along with high system availability for condensed and soft matter research, an optimized liquid hydrogen Moderator circuit has been developed. Hydrogen with a pressure around 1 MPa, a temperature around 20 K, and a para-hydrogen fraction of at least 0.995 will be utilized to interact with neutrons in a unique cold Moderator vessel arrangement. Hydrogen conversion from ortho- to para-hydrogen will be controlled using a catalyst. Two turbo pumps are arranged in series and circulate the cryogen. A helium refrigerator, the Target Moderator Cryoplant (TMCP), continuously recools the hydrogen mass flow. Pressure stabilization is achieved by a pressure control buffer. The individual ESS Cryogenic Moderator System (CMS) components, the first and second generation of hydrogen Moderators (BF1 and BF2) and a first draft of a deuterium Moderator upgrade are presented.

Identification of medium range order defects and their critical effect on spallation of Cu64Zr36 metallic glass

The absence of a well-defined structural defect is a longstanding problem, acting as the obstacle for understanding of mechanical behavior in metallic glasses. Here, through a compelling integration of experimental and computational technologies containing Synchrotron X-ray diffraction, extended X-ray absorption fine structure spectroscopy (EXAFS) as well as atomistic simulations, we present more direct evidences for the existence of medium range order (MRO) defects based on the discontinuity of stiff icosahedral network. As revealed by the numerical simulation of spallation process for two Cu64Zr36 metallic glasses with different cooling history, the MRO defects can be used as the efficient predictor of void nucleation, as evidenced by the strong correlation between high MRO defects location and subsequent void sites. This observation implies that the initial distribution as well as further generation of MRO defects play a critical role for the mechanical failure process of metallic glasses. It can be also extended to experimental conditions since the atomic packing of metallic glasses in molecular dynamic (MD) simulations is in great agreement with that obtained from reality as characterized by results of X-ray and EXAFS.

Beam dynamics studies for fast beam trip recovery of the Japan Atomic Energy Agency accelerator-driven subcritical system

High reliability and availability are primary goals for the operation of particle accelerators, especially for accelerator-driven subcritical systems (ADS). ADSs employ high-power beams for the transmutation of minor actinide; as a result, the amount and the radiotoxicity of the nuclear waste are considerably reduced. To this end, the Japan Atomic Energy Agency is designing a 30-MW continuous wave (cw) superconducting proton linear accelerator (linac) that supplies neutrons to an 800-MW subcritical reactor by a spallation process. The major challenge for an ADS linac is the strict control of the beam trip duration and its frequency to avoid thermal stress in the subcritical reactor structures. The maximum allowed beam trips for failures longer than a few seconds are estimated to be far below the rate achieved in current accelerators. Thus, we implemented a combination of hot standby and local compensation that enables a fast beam recovery. This work comprehensively investigated the tolerance of our linac lattice for the local compensations for failures in superconducting cavities and magnets. This scheme includes simultaneous compensation of multiple cavities in independent and same cryomodules that significantly enhance the reliability of the linac. The retuned schemes present acceptable beam performance to guarantee the integrity of the linac and the beam transport to the target; moreover, they satisfy the beam stability in the beam window. In addition, the readjusted elements are subjected to moderate stress to ensure a sustainable operation. This manuscript reports the beam dynamics results toward fulfilling the high reliability demanded by an ADS linac.

Erosion-corrosion behavior of Ni-20Cr-4Fe and Ni-20Cr-4Fe-7Mo under fluidized-bed biomass boiler conditions

The erosion-corrosion rate of the Mo-free alloy decreased over time because of a reduction in the erosion rate of the oxide scale associated with the transition of the scale from Ni-rich to Cr-rich. In contrast, the Mo-containing alloys displayed accelerated erosion-corrosion because of the repeated erosion of Ni-rich oxide layer and spallation of the oxide scale. The volatilization of Mo oxychloride resulted in the formation of an inner porous oxide layer which results in enhanced spallation of the oxide scale by the impact of sand particles. These volatilization and spallation processes were found to enhance the erosion-corrosion of Mo-containing alloys.

Accretion regions of meteorite parent bodies inferred from a two-endmember isotopic mixing model

ABSTRACT The diverse isotopic anomalies of meteorites demonstrate that the protoplanetary disc was composed of components from different stellar sources, which mixed in the disc and formed the planetary bodies. However, the origin of the accretion materials of different planetary bodies and the cosmochemical relationship between these bodies remain ambiguous. The noncarbonaceous (NC) planetary bodies originate from the inner solar system and have isotopic compositions distinct from those of the carbonaceous (CC) bodies. We combined Ca, Ti, Cr, Fe, Ni, Mo, and Ru isotopic anomalies to develop a quantitative two-endmember mixing model of the NC bodies. Correlations of the isotopic anomalies of different elements with different cosmochemical behaviors originate from the mixing of two common endmembers. Using this mixing model, we calculated the isotopic anomalies of NC bodies for all the considered isotopes, including the isotopic anomalies that are difficult to measure or have been altered by spallation processes. The mixing proportion between the two endmembers in each NC body has been calculated as a cosmochemical parameter, which represents the compositional relationship of the accretion materials between the NC bodies. Using the calculated mixing proportions, the feeding zones of the NC bodies could be estimated. The estimated feeding zones of NC bodies indicate a large population of interlopers in the main asteroid belt and an indigenous origin of Vesta. The feeding zones estimated in different planet formation scenarios indicate that the orbits of Jupiter and Saturn during formation of terrestrial planets were likely to be more circular than their current ones.

Spallation on Carbon Ablators

A comprehensive analysis of publicly available research statements on spallation processes of ablative heat shield materials is presented. Based on the published data and numerical simulations thereof, a definition of spallation with respect to its fundamental parameters is given. Results from ablation and spallation experiments as well as analytical and numerical models are compared and discussed with respect to the conditions and mechanisms that lead to spallation. The driving mechanisms are oxidation, pyrolysis gas outflow, shear forces, and thermal stress. Based on the summary of the current state-of-knowledge of spallation, propositions are made for future experimental and numerical investigations.

The Effect of Compression on the Void Coalescence under Strong Dynamic Loading

The void coalescence under strong dynamic loading is a significant spallation process for ductile metals. Since the spallation is basically dominated by tension waves, most void coalescence studies have focused on the tension effect. However, it is known that in spallation, the material initially undergoes a strong compression wave, and then an irreversible deformation is produced by the compression wave inside the material. Therefore, in this paper, the effect of compression on the void coalescence is investigated using the molecular dynamics (MD) simulation. It was found that as the compressive strain increases, the yield strength decreases first and then increases. The results showed that due to the Bauschinger effect (BE), the yield strength decreases by 19.43% from 5.66 GPa without compressive loading to 4.56 GPa when the compressive strain is −7.5%, after which the yield strength increases. The voids do not coalesce when the compressive strain is −8%. In addition, it was found that during the compressive phase, the void surfaces would generate dislocations, which could obstruct the void coalescence in the tensile phase. Furthermore, under compressive loading, the temperature effect on the void coalescence was studied, and it was found that lower temperatures could suppress the void coalescence.

Radioactive Elements Production in Vital Accelerator Head by 15 Mev Photon Activation and Spallation Processes

Radioactive Elements Production in Vital Accelerator Head by 15 Mev Photon Activation and Spallation Processes