Enhancement of hydrogen isotope retention capacity for the impurity deposited tungsten by long-term plasma exposure in LHD

The stress relieved tungsten samples were placed at three positions, PI (sputtering erosion dominated area), DP (deposition dominated area) and HL (Higher heat load area) during 15th plasma experiment campaign in Large Helical Device (LHD) at National Institute for Fusion Science (NIFS), Japan and were exposed to ～ 6700 shots of hydrogen plasma in a 15th long-term experiment campaign in LHD. Thereafter, the additional deuterium ion implantation to these tungsten samples was performed to evaluate the change of hydrogen isotope retention capacity in the samples by long-term plasma exposure. It was found that the carbon-dominant mixed-material layer with more than 100 nm thickness was formed on a wide area of the tungsten surface. The thicker mixed-material layer was formed on the DP sample, where the deuterium retention was about 21 times as high as that for pure W. The major desorption temperature of deuterium was shifted toward higher temperature side, which was comparable to the trapping characteristic of carbon or irradiation damages.     

Deuterium permeation in tungsten by mixed ion irradiation

Deuterium ion driven permeation was studied for mixed ion irradiation conditions with He and C. Addition of He greatly reduced permeation, while addition of C enhanced permeation. These phenomena are strongly temperature dependent, but both are significant around surface temperature of blankets (～800 K). Permeation flux has very weak dependence on microstructure. These results are important for evaluation of T behavior in blanket first walls.     

低能氦离子辐照诱导的钨材料结构演化

在温度为923 K、氦离子流强为7×10~(21) m~(-2)·s~(-1)的条件下,考察了低能氦离子辐照对钨材料表面结构的影响。采用扫描电子显微镜(Scanning Electron Microscope,SEM)、导电原子力显微镜(Conductive Atomic Force Microscope,CAFM)、称重法、X射线衍射(X-ray Diffraction,XRD)以及电子背散射衍射(Electron Back-Scattered Diffraction,EBSD)对辐照后钨材料的结构演化规律进行了分析。SEM和CAFM的研究表明,在辐照初期样品表面形成了纳米尺寸的氦泡,随着辐照剂量的增加,氦泡的尺寸和密度逐渐增加,最终引起钨表层的剥落。质量损失和溅射产额的分析结果表明,钨材料表层的剥落是钨损伤的主要形式。SEM、XRD和EBSD的分析证实了辐照后钨样品的表面形貌变化与晶体取向之间具有很强的关联性。研究结果表明,相对于(101),氦原子更容易在(111)和(001)等晶面上吸附、扩散和聚集,这些研究结果将为面向等离子体材料的优化设计提供有用的参考。     

Simulation of displacement cascades in tungsten irradiated by fusion neutrons

Numerical calculations of damage in tungsten irradiated by fusion neutrons were performed using molecular dynamics simulations combined with an embedded atom method potential. The displacement cascade efficiency has been calculated using the ratio of the number of Frenkel pairs determined by molecular dynamics simulations to the number of Frenkel pairs derived from Norgett-Robinson-Torrens formula. The cascade efficiency decreases as the Primary Knock Atoms increases. The Norgett-Robinson-Torrens calculations overestimate the Frenkel pair defect production by a factor of 2. The changes in the cascades dimensions at the early stages after irradiation indicate that the tungsten interstitials are more mobile than the vacancies. We found that the most common types of defects are single vacancies, di-vacancies, vacancy-clusters, interstitials and small number of interstitial clusters containing more than three atoms.     

Deuterium retention in tungsten at fluences of up to 10 D/m using D ion beams

Deuterium retention in two types of polycrystalline tungsten (PCW) was studied as a function of incident ion fluence, ion energy, and specimen temperature. (i) D retention at 300 K, as a function of D⁺ fluence, demonstrated a trend to saturation in both the Rembar hot-rolled thin foil and Plansee tungsten plate. At 500 K, new D retention results for the Plansee PCW showed an increasing trend with increasing incident D⁺ fluence without any indication of saturation, in agreement with previous results for Rembar PCW [A.A. Haasz, J.W. Davis, M. Poon, R.G. Macaulay-Newcombe, J. Nucl. Mater. 258-263 (1998) 889-895]. Even when the incident D⁺ fluence was increased to 8 × 10²⁵ D⁺/m², which is in the fluence range of plasma devices, there was still no sign of saturation. (ii) The temperature dependence results for the Plansee PCW show a decreasing trend in D retention as the temperature is increased from 300 to 500 K. These results differ from previous studies of Rembar PCW [A.A. Haasz, J.W. Davis, M. Poon, R.G. Macaulay-Newcombe, J. Nucl. Mater. 258-263 (1998) 889-895], but are similar to those seen for single crystal tungsten [M. Poon, A.A. Haasz, J.W. Davis, R.G. Macaulay-Newcombe, J. Nucl. Mater. 313-316 (2003) 199]; an explanation for the different behaviour is suggested. (iii) Varying the D⁺ energy from 100 to 500 eV/D⁺ plays a minor role in the amount of D retained, suggesting that D retention in W depends more on the W structure, incident ion fluence and specimen temperature, rather than on the incident ion energy when the energy is below the threshold for damage formation (∼960 eV for D on W).     

Comparison of radiation damage in silicon induced by proton andneutron irradiation

The subject of radiation damage to Si detectors induced by 24-GeV/c protons and nuclear reactor neutrons has been studied. Detectors fabricated on single-crystal silicon enriched with various impurities have been tested. Significant differences in electrically active defects have been found between the various types of material. The results of the study suggest for the first time that the widely used nonionizing energy loss (NIEL) factors are insufficient for normalization of the electrically active damage in case of oxygen- and carbon-enriched silicon detectors. It has been found that a deliberate introduction of impurities into the semiconductor can affect the radiation hardness of silicon detectors     

Investigating permeation and transport of H isotopes in tungsten by first-principles

We have investigated permeation and transport of hydrogen (H) isotopes in tungsten (W) single crystal employing first-principles calculations in junction with Fick’ law. Permeability was approximately evaluated according to the solubility and diffusion coefficient of H. The solubility for H in bulk W from present calculation is consistent with the experimental results measured by Frauenfelder. The permeation fluxes of H isotopes are examined at the different thickness of W wall. The permeation fluxes of deuterium with the W thickness of 21 μm at the temperature of 770 K and with the W thickness of 50 μm at the temperature of 893 K were 0.68 × 10¹³ atom/m²s and 0.34 × 10¹⁴ atom/m²s, respectively. The dissociation coefficients of H isotopes are also evaluated. We believe that the present first-principles combined with Fick’ law method can be also generalized to investigate permeation and transport of H isotopes in most metals since such H isotopes behaviors in most metals are similar to those of H isotopes in W.     

Characterization of displacement cascade damage produced in Cu3Au by fast-particle irradiation

Zones of reduced long-range order created at displacement cascade sites in well-ordered Cu₃Au may be directly imaged in the transmission electron microscope so that quantitative information can be obtained on individual cascade events. This technique has been used to characterise the cascade damage created by three fast particles (3.5 MeV protons, a source of moderated fission neutrons and a source of fusion neutrons with energies peaking at 14.8 MeV) with the aim of comparing the experimental observations with the relevant collision models. In each case, disordered zone number densities, sizes and shapes were determined, and were found to be characteristic of each irradiation, with the sizes of disordered zones and the proportion of zones of complex shape increasing on going from 3.5 MeV protons to fission neutrons to fusion neutrons. The quantitative results are largely consistent with the different calculated primary recoil spectra, although in the fusion neutron case some discrepancies are found which cannot readily be explained by limitations in the experimental technique. More specifically, more and larger disordered zones are found than expected from the calculated recoil spectrum. Subcascade formation was observed only in the neutron irradiations, with the distributions of sizes and shapes of individual sub-cascades being very similar in the two cases (in marked contrast to those obtained from sizing total cascade events). Finally, the production of point-defect clusters at cascade sites was studied. The efficiency of cascade collapse increased on going from 3.5 MeV protons to fission neutrons to fusion neutrons.     

Deuterium recovery from water–isotope mixture by thermal diffusion in countercurrent-flow Frazier scheme inclined for improved performance

The theory for recovery of deuterium from water isotope mixture by thermal diffusion in countercurrent-flow inclined Frazier scheme has been developed and investigated. The equations for the optimal angles of inclination and the corresponding best performances were derived. Considerable improvement in performance is obtained when the Frazier scheme is operated at the optimal angle of inclination. Further improvement can be achieved if the operation is conducted in countercurrent flow, instead of being in cocurrent flow.     

Catastrophic processes in dielectrics in irradiation by high-current electron beams

The results of the research in explosive decomposition of heavy metal azides initiated by electric (“streamer”) charges induced by high-current electron beam have been considered. A physical model for initiation of heavy metal azides explosive decomposition by electron beam has been suggested. The model suggests formation of strong electric field in the sample and its neutralization by ultrasound anode charges. The streamer front generates “hot spots” which start the formation of explosive decomposition sites in a condensed reactive material.     

Transient processes induced by heavy projectiles in silicon

The thermal spike model developed for the electronic stopping power regime is extended to consider both ionization and nuclear energy loss processes of the projectile as electronic and atomic heat distinct sources. The time and space dependencies of the lattice and electron temperatures near the projectile trajectory are calculated and discussed for different ions in silicon, at room and cryogenic temperatures, taking into account the peculiarities of electron-phonon interaction in both domains. The model developed contributes to the understanding of transient microscopic processes immediately after the projectile interaction in the target.     

X射线辐照诱导人神经胶质瘤细胞DNA双链损伤研究

采用免疫荧光染色法检测X射线诱导M059K细胞磷酸化组蛋白H2AX(γH2AX)和磷酸化的毛细血管扩张性共济失调症突变基因(pATM)焦点的形成;流式细胞仪分析M059K细胞γH2AX和pATM表达的周期依赖性。免疫荧光染色检测结果显示,γH2AX和pATM焦点阳性细胞分别以照射后0.5、4 h表达最高,照射后24h,高剂量组焦点阳性细胞达100%。流式细胞仪分析结果显示,γH2AX和pATM的表达具有细胞周期依赖性。照射后0.5、4 h,γH2AX和pATM在细胞各期的表达均明显增加,并以G0/G1期为著;照射后24 h,γH2AX和pATM在G0/G1和S期表达降低,而G2/M期细胞表达明显增加。细胞呈现明显的G2/M期阻滞。结果提示,γH2AX和ATM信号通路参与X射线诱导的M059K细胞DNA双链断裂。     

Estimation of plasma density perturbation from dusty plasma injection by laser irradiation on tungsten target in DiPS

To investigate the interaction of dusty plasma with magnetized plasmas at divertor plasma simulator, radial profiles of plasma density(ne) and electron temperature were measured in terms of plasma discharge currents and magnetic flux intensity by using a fast scanning probes system with triple tips. Dusty plasma with dusts(a generation rate of 3 μg s~(-1) and a size of 1–10 μm)was produced via interactions between a high-power laser beam and a full tungsten target. As ne increases, the scale of the effects of dusty plasma injection on magnetized plasmas was decreased. Also, the duration of transient fluctuation was reduced. For numerical estimation of plasma density perturbation due to dusty plasma injection, the result was ~10% at a core region of the magnetized plasma with n_e of(2–5)×10~(11) cm~(-3) at steady state condition.     

Simulation of damage induced by ion implantation in Lithium Niobate

A simulation tool has been developed to engineer the damage formation in Lithium Niobate by ion irradiation with any atomic number and energy. Both nuclear and electronic processes were considered and, in particular, the dependence on the ion velocity of the electronic excitation damage efficiency has been taken into account. By using this tool it is possible both to draw damage nomograms, useful to qualitatively foresee the result of a given process, and to perform reliable simulations of the defect depth profiles, as demonstrated by the good agreement with the experimental data available in the literature.     

Changes in metal nanoparticle shape and size induced by swift heavy-ion irradiation

Changes in the shape and size of Co, Pt and Au nanoparticles induced by swift heavy-ion irradiation (SHII) have been characterized using a combination of transmission electron microscopy, small-angle X-ray scattering and X-ray absorption near-edge structure. Elemental nanoparticles of diameters 2-15 nm were first formed in amorphous SiO₂ by ion implantation and thermal annealing and then irradiated at room temperature with 27-185 MeV Au ions as a function of fluence. Spherical nanoparticles below a minimum diameter (4-7 nm) remained spherical under SHII but progressively decreased in size as a result of dissolution into the SiO₂ matrix. Spherical nanoparticles above the minimum diameter threshold were transformed to elongated rods aligned with the ion beamdirection. The nanorod width saturated at an electronic energy deposition dependent value, progressively increasing from 4-6 to 7-10 nm (at 5-18 keV/nm, respectively) while the nanorod length exhibited a broad distribution consistent with that of the unirradiated spherical nanoparticles. The threshold diameter for spherical nanoparticle elongation was comparable to the saturation value of nanorod width. We correlate this saturation value with the diameter of the molten track induced in amorphous SiO₂ by SHII. In summary, changes in nanoparticle shape and size are governed to a large extent by the ion irradiation parameters.     

Evidence of nanostructure formation in Ge oxide by crystallization induced by swift heavy ion irradiation

Ge oxide films were irradiated with 150 MeV Ag ions at fluences varying between 10¹² and 10¹⁴ ions/cm². The irradiation-induced changes were monitored by FT-IR spectroscopy, atomic force microscopy, X-ray diffraction and photoluminescence spectroscopy. The FT-IR spectra indicate stoichiometric changes and an increase in Ge content on irradiation. X-ray diffraction shows a crystallization of the irradiated films and presence of both Ge and GeO₂ phases. The Ge nanocrystal size, as calculated from Scherrer’s formula, was around 30 nm. The morphological changes, observed in atomic force microscopy, also indicate formation of nanostructures upon ion irradiation and a uniform growth is observed for a fluence of 1 × 10¹⁴ ions/cm².     

线粒体基因组D-loop区变异及辐射诱发突变

线粒体基因组D环区作为非编码区,控制着mtDNA的复制与转录,由于自身的结构和功能特点,极易发生变异.变异形式包括突变和多态性,这些变异在疾病的发生和发展过程中起着非常重要的作用.此外,本文还简要介绍了辐射诱导的D环区突变的研究现状及其前景.     

酸性鞘磷脂酶活化在微波辐照致神经细胞凋亡中的作用研究

为阐明微波辐照致神经细胞酸性鞘磷脂酶（Acid Sphingomyelinase,ASM）活化的规律,揭示ASM活化在微波辐照致神经细胞凋亡中的作用,以原代培养神经元细胞,采用30W／era2微波辐照10min,采用Hoechst33342荧光染色观察细胞凋亡,以ASM活性测定试剂盒测定ASM活性,RT-PCR、western blot分别检测ASM基因和蛋白表达的变化。用ASM活性抑制剂米帕明预处理,观察微波辐照后神经细胞凋亡情况。研究发现,微波辐照引起海马神经元细胞发生凋亡,神经元ASMmRNA和蛋白表达上调,ASM酶活性增高,给予ASM活性抑制剂米帕明预处理后,可部分拮抗微波辐照引起的神经细胞凋亡率增加。结果提示,微波辐照引起神经细胞ASM活化及表达上升,ASM活化在微波辐照所致的神经细胞凋亡中起重要作用。     

Morphological change in FePt nanogranular thin films induced by swift heavy ion irradiation

We have investigated morphology change of FePt nanogranular films (FePt)₄₇(Al₂O₃)₅₃ under irradiation with 210 MeV Xe ions. Here, electron tomography technique was extensively employed to clarify three-dimensional (3D) structure in irradiated specimens, in addition to conventional transmission electron microscopy (TEM) techniques such as bright-field observation and scanning TEM energy dispersive X-ray spectroscopy (STEM-EDX) analysis. The ion irradiation induces the coarsening of FePt nanoparticles with elongation along the beam direction. Electron tomography 3D reconstructed images clearly demonstrated that when the fluence achieves 5.0 × 10¹⁴ ions/cm², well-coarsened FePt balls have been formed on the irradiated surface, and the particles in the film interior have been deformed into rods along the ion trajectory. The alloy particles become inhomogeneous in composition after prolonged irradiation up to 1.0 × 10¹⁵ Xe ions/cm². The particle center is enriched with Pt, while Fe is slightly redistributed to the periphery.