Mechanodynamic penetration of helium atoms into aluminum and its alloys under strain in liquid helium

The specific features of helium penetration into aluminum and its alloys, V95 and D16T, at a temperature of 4.2 K under uniaxial tension, compression, and reversal of the sign of the load are investigated. The role played by serrated strain in the intensity of the effect under consideration and the influence of impurities on the number of helium atoms penetrating into strained samples are elucidated. It is shown that the condition of additivity of the effect observed under successive reversal of the sign of the load depends on the specific features of the tensile and compressive strains.     

Stopping power of low-energy deuterons in 3He gas

The stopping power of atomic and molecular deuterons in ³He gas was measured over the range E _d = 10 to 100 keV using the ³He pressure dependence of the ³He(d,p) ⁴He reaction yield. At energies above 30 keV, the observed stopping power values are in good agreement with a standard compilation. However, near 18 keV the experimental values drop by a factor 50 below the extrapolated values of the compilation. In a simple model, the behavior is due to the minimum 1s↦2s electron excitation of the He target atoms (= 19.8 eV, corresponding to E _d = 18.2 keV), i.e. it is a quantum effect, by which the atoms become nearly transparent for the ions.     

Stopping power in insulators and metals without charge exchange

The slowing-down process of pointlike charged particles in matter has been investigated by measuring the stopping power for antiprotons in materials of qualitatively very different nature. Whereas the velocity-proportional stopping power observed for metal-like targets such as aluminum over a wide energy range of 1-50 keV is in agreement with expectations, it is surprising that the same velocity dependence is seen for a large band-gap insulator such as LiF. The validity of these observations is supported by several measurements with protons and several checks of the target properties. The observations call for both a qualitative explanation and a quantitative theoretical model.     

Stopping power of fast channeled protons in Hartree-Fock approximation

The electronic energy loss of MeV-protons in crystals is investigated in the Hartree-Fock approximation for the core electrons of the target. It turns out that each core electron can be regarded as stopping the proton independent of all other electrons without restriction by the Pauli principle. For the channeling stopping power the impact parameter dependent energy loss of a proton moving rectilinearly past a crystal ion is calculated in first Born approximation. Low excitations of the core electrons lead to a long range impact parameter dependence, whereas high excitations contribute to the energy loss proportional to the electron density sampled along the proton trajectory. The results are applied to 4 MeV proton channeling along the main channels of Si using Clementi wave functions for the core electrons and a free electron approximation for the valence electrons. The comparison with the experimental results of Clarket al. yields good agreement. In the high velocity limit a reduction of the channeling stopping power to 0.64(0.83) of the random value is predicted for Si(C).     

Stopping power of polymers for heavy ions: a comparative study

A comparative study of various stopping power tables and codes for heavy ions in polymers has been made by comparing the computed stopping power values with the corresponding experimental values. The energy loss of different heavy ions (3≤Z ₁≤29) in the energy domain of ～0.19–3.14 MeV/n has been studied in six different polymers mostly used as particle track detectors viz: Mylar (Polyethylene Terephthalate), PEN (Polyethylene Napthalate), Polycarbonate, CR-39 (Polyallyl Diglycol Carbonate), Kapton (Polypyromellitimide) and LR-115 (Cellulose Nitrate). The merits and demerits of the adopted formulations are highlighted. It has been observed that the calculations based on SRIM2003.26 and tables of ICRU-73 provide best agreement with the experimental data for projectiles (3≤Z ₁≤29) and (3≤Z ₁≤18), respectively. The MSTAR3.12 code shows good results for projectiles (3≤Z ₁≤18), except in case of CR-39 for O, Na, and Al projectiles. The statistical analysis on the basis of combined error reveals that the SRIM2003 and ICRU-73 tables are more reliable as compared to the other programs taken in the present study, whereas CasP3.1 is least reliable program in lower energy domain.     

Critical power for self-focussing of a femtosecond laser pulse in helium

The critical power for self-focussing of a femtosecond laser pulse in helium has been measured using the moving focus method. The experimental value is (1 atm) ∼268 GW. Using this value, the nonlinear refractive index is inferred to be  ∼ 3.6 × 10^-21 cm²/W. In addition, the plots of the electron densities versus energy and pressure have also been used to determine the critical power of helium, based on the intensity clamping of the filamentation process. The value agrees well with the one by the moving focus method.     

Stopping power and straggling of energetic light ion beams in yttrium

Energy loss and straggling for protons, deuterons and α-particles in yttrium were measured in the energy region between 0.15 MeV and 2.5 MeV. The measured stopping powers of the hydrogen ions agree reasonably well with the semi-empirical values of Andersen and Ziegler, although better agreement was found with the values of Janni. For helium ions there are a marked difference with the values of Ziegler. Below 200 keV/amu the stopping ratios of the helium and hydrogen ions are lower than Ziegler's master curve. The straggling values of the hydrogen ions are about 15% lower than the Bohr estimate, while the straggling of the helium ions reach the Bohr value at about 0.2 MeV/amu.     

The energy straggling of hydrogen and helium ions in aluminum and polystyrene

The energy straggling of H⁺ and He⁺ ions in aluminium and polystyrene films has been measured in energy interval 0.1–1.2 MeV. A new version of the theory, which takes into account fluctuations of ion charge, is suggested for analysis the results obtained.     

冲击加载下铝中氦泡和孔洞的塑性变形特征研究

通过分子动力学模拟研究了在相同冲击加载强度下单晶铝中氦泡和孔洞的塑性变形特征,结果发现氦泡和孔洞的塌缩是由发射剪切型位错环引起的,而没有观测到棱锥型位错环发射. 氦泡和孔洞周围的位错优先成核位置基本一致,但是氦泡周围发射的位错环数目比孔洞多,位错环发射速度明显比孔洞快. 且氦泡和孔洞被冲击波先扫过部分比后扫过部分发射位错困难. 通过滑移面上的分解应力分析发现,氦泡和孔洞周围塑性特征的差别是由于氦泡内压引起最大分解应力分布改变造成的. 氦泡和孔洞被冲击波先后扫过部分塑性不对称是因为冲击波扫过时引起形状变化, 关键词： 分子动力学 冲击波 氦泡 孔洞     

氦泡对铝的弹性性质的影响

主要利用分子动力学方法模拟计算了含氦泡的铝的弹性性质,首先,应用第一性原理的方法计算了Al-He的相互作用势.其次,从两个不同的方面研究了氦泡对铝弹性常数的影响,一是不同的氦泡尺寸(直径分别是16, 20, 25, 30和3.5nm),二是不同的氦泡压力(即固定氦泡大小,氦泡内氦原子的个数与空位的比分别大约是5％,15％,45％ 和85％).结果表明弹性常数随着氦泡半径的增大而减小,对于固定大小的氦泡,随着氦泡内的压力变化弹性常数基本保持恒定.最后通过建立弹性复合体模型,得到的解析解定性上解释了氦泡的大小以及内压对铝的弹性常数的影响,与分子动力学模拟结果吻合. 关键词： 辐照损伤 氦泡 分子动力学 弹性常数     

Stopping power of an electron gas: The sum rule approach

The stopping power of dense electron plasmas is determined using a simplified version of the method of moments based on some interpolation formulas for the sum rules of the loss function. The energy losses of ions are evaluated with various projectile charges moving in a plasma at different values of the coupling and degeneracy parameters. The losses of slowly moving charged particles are closely examined. The results obtained are compared with those of some alternative approaches and the particle‐in‐cell (PIC) simulation data.     

Optimal wire-number range for high x-ray power in long-implosion-time aluminum Z pinches

Experiments performed on the 8-MA Saturn accelerator to investigate the effects of interwire gap spacing on long-implosion-time Z pinches have resulted in the observation of a regime of optimal wire number. The experiments varied the wire number of 40 and 32 mm diam arrays, resulting in interwire gaps from 3.9 to 0.36 mm, with fixed mass and length. aluminum K-shell powers up to 3.4 TW were measured, with long, slow rising, lower power x-ray pulses for interwire gaps greater than 2.2 mm and less than 0.7 mm, and short, fast rising, higher power pulses for interwire gaps in the range 0.7-2.2 mm.     

Stopping power of some elemental and complex SSNTD media at low energies

Stopping power calculations using Hubert et al. formulation have been extended beyond its recommended range of validity, i.e. 2.5–500 MeV/n. It has been established that, for elemental targets up to copper and for complex polymeric SSNTD materials, e.g. CR-39, LR-115, Mylar and Kapton, the formulation provides good agreement with experimental data for projectiles with Z≤29 down to energies as low as 0.5 MeV/n.     

Stopping power for Ge ions produced by inelastic scattering of (d,t) fusion neutrons

Excited⁷²Ge projectiles are produced with 15MeV neutrons from a (d, t) fusion reaction, recoiling within a Ge(Li) detector. The relative response r of the detector on the kinetic energy released by those⁷²Ge ions which are produced in a head-on collision was determined to be r=0.437±0.024 (for E_Ge=800 keV). This value is correlated to the ratio between nuclear and electronic energy loss.     

Dynamical response of helium bubble motion to irradiation with high-energy self-ions in aluminum at high temperature

Brownian-type motion of helium bubbles in aluminum and its dynamical response to irradiation with 100-keV Al⁺ ions at high temperatures has been studied using in situ irradiation and transmission electron microscopy. It is found that, for most bubbles, the Brownian-type motion is retarded under irradiation, while the mobility returns when the irradiation is stopped. In contrast, under irradiation, a small number of bubbles display exceptionally rapid motion associated with the change in bubble size. These effects are discussed in terms of the dynamical interaction of helium bubbles with cascade damage formed by the high-energy self-ion irradiation.     

Characterization of Si-added aluminum oxide (AlSiO) films for power devices

Synthesis of Si-added aluminum oxide (AlSiO) films is attempted as an insulating film with both a wide bandgap and a high dielectric constant. Electrical characteristics of AlSiO films are investigated. Leakage current of the AlO film is suppressed by Si addition and is minimized with Si composition ratio of 12%. Capacitance versus voltage (C-V) measurements are carried out for Au/AlSiO/Si MIS structure. Both flat band shift and hysteresis of the C-V characteristics are suppressed by Si addition. A low leakage current is demonstrated for Au/AlSiO/n-SiC MIS structure.