共查询到20条相似文献,搜索用时 15 毫秒
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Ab initio calculations based on density functional theory have been performed to study the dissolution and migration of helium, and the stability of small helium-vacancy clusters HenVm (n, m=0-4) in aluminum. The results indicate that the octahedral configuration is more stable than the tetrahedral. Interstitial helium atoms are predicted to have attractive interactions and jump between two octahedral sites via an intermediate tetrahedral site with low migration energy. The binding energies of an interstitial He atom and an isolated vacancy to a HenVm cluster are also obtained from the calculated formation energies of the clusters. We find that the di- and tri-vacancy clusters are not stable, but He atoms can increase the stability of vacancy clusters. 相似文献
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Transmission electron microscopy has been used to study the thermal annealing of radiation induced defect clusters in tungsten irradiated at reactor ambient tempeaature, ~ 70°C. Annealing, consisting of the growth and eventual elimination of the clusters, is observed to occur in two stages, one at temperatures below 435°C and one at temperatures above 740°C, which are interpreted as being due to interstitial and vacancy migration, respectively. The changes in defect cluster size and density are paralleled by similar changes in the measured strength of the material, and can be quantitatively correlated with the shear stress on the basis of a model of dislocation movement through a random array of obstacles. 相似文献
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运用分子动力学方法研究了不同He浓度和不同级联能下含He的α-Fe低温时的位移级联过程.模拟的主要撞击原子(PKA)的能量(EP)(即级联能)从500eV变化到5keV,辐照温 度为100K,He的浓度从1%变化到5%.比较了不同He浓度下的Fe-He混合物和纯α-Fe的位移级 联过程,发现在含有He的α-Fe中总的Fe和He的Frenkel对与纯的α-Fe的Frenkel对的数目相 当.当He的浓度较低时,含有He的α-Fe中的Frenkel对比α-Fe的要低,随He的浓度增加,有 He的α-Fe中的Frenkel对比α-Fe中的高,这主要与He在金属中的性质有关.本研究证明了位 移级联过程可以直接导致He泡的成核.对不同级联能和不同He浓度下Fe的位移级联过程的模 拟,发现在同样的级联能下,随着He浓度的增加,He成团的几率增大;在同样的He浓度下, 随着级联能的增加,He成团的几率也同样增加,并分析了级联下He泡的形成机制.
关键词:
Fe
位移级联
He-空位复合物
分子动力学 相似文献
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It is shown that a very long-range, dispersive-type interaction exists between voids in metals which may contribute to the void crystalization phenomenon. 相似文献
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Sedgwick H Kroy K Salonen A Robertson MB Egelhaaf SU Poon WC 《The European physical journal. E, Soft matter》2005,16(1):77-80
To understand the non-equilibrium behavior of colloidal particles with short-range attraction, we studied salt-induced aggregation of lysozyme. Optical microscopy revealed four regimes: bicontinuous texture, beads, large aggregates, and transient gelation. The interaction of a metastable liquid-liquid binodal and an ergodic to non-ergodic transition boundary inside the equilibrium crystallization region can explain our findings. 相似文献
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N. V. Kamyshanchenko V. V. Krasil’nikov N. V. Neklyudov A. A. Parkhomenko 《Physics of the Solid State》1998,40(9):1482-1485
The development of plastic instability in the initial deformation stages of irradiated materials is studied. The dependence
of the fraction of dislocations which overcome obstacles in the dynamic regime (dislocation “channeling”) on the degree of
radiation hardening (irradiation dose) and the dislocation velocity is analyzed. It is shown that this effect plays a role
in radiation embrittlement of reactor materials.
Fiz. Tverd. Tela (St. Petersburg) 40, 1631–1634 (September 1998) 相似文献
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Experimental observations of dislocation decoration with self-interstitial atom (SIA) clusters and of SIA cluster rafts are analysed to establish the mechanisms controlling these phenomena in bcc metals. The elastic interaction between SIA clusters, and between clusters and dislocations is included in kinetic Monte Carlo (KMC) simulations of damage evolution in irradiated bcc metals. The results indicate that SIA clusters, which normally migrate by 1D glide, rotate due to their elastic interactions, and that this rotation is necessary to explain experimentally-observed dislocation decoration and raft formation in neutron-irradiated pure iron. The critical dose for raft formation in iron is shown to depend on the intrinsic glide/rotation characteristics of SIA clusters. The model is compared with experimental observations for the evolution of defect cluster densities (sessile SIA clusters and nano-voids), dislocation decoration characteristics and the conditions for raft formation. 相似文献
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Various mechanisms of recombination of electrons with multiply charged atomic ions in atomic clusters irradiated by superintense femtosecond laser pulses are discussed. All of the recombination mechanisms are shown to take a time considerably longer than the laser pulse duration and, hence, they can develop only in a homogeneous, fairly rarefied cluster plasma after pulse termination. All autoionization states of multiply charged ions in a dense cluster plasma have been found to be destroyed by the Holtsmark electric field. 相似文献
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The effect of the size dependence of the production rate of point defect clusters is taken into account in the cluster dynamics (CD) modeling of the simultaneous formation of vacancy clusters and self-interstitial atom clusters in neutron-irradiated pure iron. The calibration of material parameters has been carried out. The correspondence between small angle neutron scattering, transmission electron microscopy and positron annihilation spectroscopy and CD data is studied. 相似文献
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M. Pietroni 《The European physical journal. Special topics》2009,168(1):149-177
All the non-trivial features of the Universe we see around us, such as particles, stars, galaxies, and clusters of galaxies,
are the result of non-equilibrium processes in the cosmic evolution. These lectures aim to provide some general background
in cosmology and to examine specific, and notable, examples of departures from thermal equilibrium. They are organized as
follows: 1) Overview of the thermal history of the Universe after the Big Bang: the relevant time-scales and the mechanism
of particle decoupling from the themal bath; 2) Explicit examples of cosmic relics: nucleosynthesis, photons and the cosmic
microwave background, neutrinos, and cold dark matter; 3) Baryogenesis: the generation of the baryon asymmetry of the Universe;
4) The formation of cosmic structures (galaxies, clusters of galaxies): from the Vlasov equation to the renormalization group. 相似文献
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用150fs的掺钛蓝宝石激光系统, 在功率密度约为5×1015 W/cm2时 激励氩(Ar)团簇,利用具有空间分辨能力的平场光栅谱仪观察到13—23nm波段Ar的软x射线谱,并观察到Ar的11阶离子谱线.在较宽的激光脉宽和较低的激光功率密度情况下,通过激励Ar团簇,获得 了Ar的高阶电离度的实验结果,且谱线的信噪比明显好于光场感应电离的情况,说明团簇的 形成大幅度地提高了激光能量的吸收效率.
关键词:
Ar团簇
超短强激光
软x射线辐射 相似文献
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A. Sagisaka H. Honda K. Kondo H. Suzuki K. Nagashima T. Kawachi A. Nagashima Y. Kato H. Takuma 《Applied physics. B, Lasers and optics》2000,71(4):549-554
X-ray spectra from nitrogen clusters irradiated with ultrashort laser pulses are reported. The line spectra of H-like and
He-like nitrogen ions have been observed by irradiation with 100 fs, 800 nm pulses at 7×1017 W/cm2 irradiance. The generation of highly charged ions of N6+ and N7+ is explained by the optical field-induced ionization and the subsequent collisional ionizations in the clusters. The He-δline
has anomalously high brightness compared to other He-like lines. It is ascribed to charge exchange, which preferentially populates
the n=5 level of N5+.
Received: 7 October 1999 / Published online: 23 February 2000 相似文献
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Namba S Hasegawa N Nishikino M Kawachi T Kishimoto M Sukegawa K Tanaka M Ochi Y Takiyama K Nagashima K 《Physical review letters》2007,99(4):043004
The interaction of large Xe clusters with a soft x-ray laser pulse having a wavelength of 13.9 nm and an intensity of up to 2x10(10) W/cm2 was investigated using a time-of-flight ion mass spectrometer. The corresponding laser photon energy was sufficiently high to photoionize Xe 4d innershell electrons. It was found that Xe3+ ions (which result from double Auger decay of 4d vacancies) became the dominant final ionic product with increasing cluster size and x-ray intensity. This is in contrast to the results of synchrotron radiation experiments involving free Xe atoms, in which Xe2+ is the dominant resultant ion species. Possible mechanisms responsible for the enhancement of the double Auger transition probability in x-ray laser and cluster interaction are discussed. 相似文献
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Coulomb expansion of deuterated methane clusters irradiated by an ultrashort intense laser pulse 下载免费PDF全文
The simulations of three-dimensional particle dynamics show that when irradiated by an ultrashort intense laser pulse, the deuterated methane cluster expands and the majority of deuterons overrun the more slowly expanding carbon ions, resulting in the creation of two separated subelusters. The enhanced deuteron kinetic energy and a narrow peak around the energy maximum in the deuteron energy distribution make a considerable contribution to the efficiency of nuclear fusion compared with the ease of homonuelear deuterium clusters. With the intense laser irradiation, the nuclear fusion yield increases with the increase of the cluster size, so that deuterated heteronuelear clusters with larger sizes are required to achieve a greater neutron yield. 相似文献
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在强光一号脉冲加速器上进行了国内首次的实验室软X光辐射三种材料的喷射冲量研究。结果表明,在能量为(0.2~0.33)keV、平均脉宽为39ns左右的X光辐射下,对灰漆、白漆和硬铝,在能注量分别为(92~152)J/cm2、(115~136)J/cm2和(163~192)J/cm2时,它们的冲量耦合系数分别为(0.61~0.80)Pa·s/(J·cm-2)、(0.58~0.97)Pa·s/(J·cm-2)和(0.61~0.84)Pa·s/(J·cm-2)。 相似文献