Room temperature aging effects of blistering and surface roughening after Ar+ ion bombardment on Mo single crystals

300 keV Ar⁺ ions are bombarded on the surface of Mo single crystals to doses of $\text{1 × 10}{}^{17}$, $\text{6.2 × 10}{}^{17}$, $\text{1 × 10}{}^{18}$ and $\text{2.8 × 10}{}^{18}$ ions/cm². After bombardment with $\text{6.2 × 10}{}^{17}$ ions/cm², blistering is observed after room-temperature aging of less than 100 days, in spite of the large sputtering yield. Disappearance of the formed blisters and concurrent surface roughening are observed with further aging. For higher dose bombardments, only surface roughening is observed without prior formation of blisters. Distribution of the injected ions associated with large sputtering yield is derived. From this distribution, the critical amount of injected ions required for blistering to occur is estimated to be equal to or less than $\text{3.4 × 10}{}^{17}$ ions/cm².     

羟基红花黄色素A对碳离子束辐照致放射性脑损伤的保护作用

探究传统活血化瘀中药红花活性成分羟基红花黄色素A(HSYA)对12C6+重离子束诱发放射性脑损伤的保护作用。昆明种小鼠60只,随机分为正常组、辐照对照组、HSYA低(5 mg/kg)、中(10 mg/kg)、高(20 mg/kg)剂量干预组。给药组于辐照前3 d起每日腹腔注射相应剂量药物,末次给药后1 h,以4.0 Gy12C6+辐照小鼠头部。辐照1个月后,通过Morris水迷宫实验检验小鼠认知功能,以伊文思蓝(EB)作为指示剂测定小鼠血脑屏障通透性,并分别用亚硝酸盐形成法和硫代巴比妥酸(TBA)法测定脑组织中超氧化物歧化酶(SOD)活性及脂质过氧化产物丙二醛(MDA)的含量。结果显示,经12C6+辐照后,单纯照射组小鼠表现出明显的认知功能障碍(P<0.01),小鼠血脑屏障通透性明显升高,脑组织SOD活性明显降低,MDA含量明显增加,羟基红花黄色素A可剂量依赖性地改善小鼠认知功能障碍,保护血脑屏障,上调SOD活性,并降低MDA含量,表明羟基红花黄色素A对12C6+重离子束诱发放射性脑损伤有保护作用。     

Synergism in sputtering of copper nanoclusters on graphite substrate at low energy Cu2 bombardment

Molecular dynamics simulation of Cu cluster sputtering by 50-200 eV/atom Cu₂ dimers and Cu single atoms has been performed. The clusters were located on a (0 0 0 1) graphite surface and consisted of 13-195 atoms. Synergy features were identified in the sputtering yield and energy distributions of sputtered particles calculated for the cases of cluster bombardment with Cu dimers and monomers at the same velocity. The reason for the nonlinear effects in surface cluster sputtering is the overlapping of collision cascades generated by each of the dimer atoms.     

Angular effects in the sputtering of Cr from stainless steel by 10 keV H3

Energy and angular distributions of Cr⁺ sputtered from stainless steel by 1.6 × 10⁻¹⁵ J (10 keV) H⁺₃ are reported as a function of angle of incidence. For more normal incidence, the peak in the energy distribution occurs in the vicinity of 3.2 × 10⁻¹⁹ J (2 eV), the average energy is approximately 1.12 × 10⁻¹⁸ J (7 eV), and the angular distribution is close to cosine. Toward glancing incidence, the peak energy increases to ˜6.4 × 10⁻¹⁹ J (4 eV), the average energy increases to ˜1.28 × 10⁻¹⁸ J (8.0 eV), and the angular distribution shows a distinct maximum in the forward direction. These results are discussed in terms of the increasing role of surface recoils in the sputtering mechanism at glancing incidence.     

Studies of 1s2s 3S-1s2p 3P transitions in helium-like Ne8+ recoil ions using photographic spectroscopy

This work describes the application of the technique of photographic VUV spectroscopy to accurate measurement of the wavelength of the theoretically interesting 1s2s ³S₁-1s2p ³P₂ transition in helium-like Ne⁸⁺ in a recoil ion source. Good resolution is obtained, and a preliminary value of 124.815±0.002 nm is found for the wavelength.     

Clarification of high density electronic excitation effects on the microstructural evolution in UO2

In order to understand the properties of ion tracks and the microstructural evolution under accumulation of ion tracks in UO₂, 100 MeV Zr¹⁰⁺ and 210 MeV Xe¹⁴⁺ ions irradiation examinations have been done at a tandem accelerator facility of JAEA-Tokai, and it has been observed the microstructure by means of a transmission electron microscope (TEM) and a scanning electron microscope (SEM) in CRIEPI.Comparison of the diameter of ion tracks between UO₂ and CeO₂ under irradiation with 100 MeV Zr¹⁰⁺ and 210 MeV Xe¹⁴⁺ ions at room temperature clarify that the sensitivity on high density electronic excitation of UO₂ is much less than that of CeO₂. By the cross-sectional observation of UO₂ under irradiation with 210 MeV Xe¹⁴⁺ ions at 300 °C, elliptical changes of fabricated pores that exist till ∼6 μm depth and the formation of dislocations have been observed in the ion fluence over 5 × 10¹⁴ ions/cm². The drastic changes of surface morphology and inner structure in UO₂ indicate that the overlapping of ion tracks will cause the point defects, enhance the diffusion of point defects and dislocations, and form the sub-grains at relatively low temperature.     

The effects of irradiation condition and microstructural change on lattice parameter, crystal lattice strain and crystallite size in high burnup UO2 pellet

Pellet samples (average burnup: 37-62 GWd/t) were prepared from three kinds of fuel rods which were irradiated in the Halden Heavy Water Reactor in Norway, and microstructural changes in the pellet samples were investigated by means of optical microscopy, SEM/EPMA and micro-X-ray diffractometry. The measured lattice parameters tended to be smaller than the values reported previously, and it is likely that the measured lattice parameters were affected by the temperature conditions during the irradiation tests and the microstructural changes which occurred in the samples. Considering the burnup dependence of uniform and non-uniform strains, the following things are suggested: the interstitial atoms which cause uniform strain begin firstly to form dislocations as a recovery process of irradiation defect and the dislocation density increases. With increasing burnup, the accumulation of dislocations in the crystallite saturates and the migration of dislocations becomes dominant as a recovery process of irradiation defects in the crystallite.     

Molecular dynamics simulations to explore the effect of chemical bonding in the keV bombardment of Si with C60, Ne60 and Ne60 projectiles

Depth profiling experiments using secondary ion spectrometry (SIMS) have shown effects that are characteristic to the pairing of the projectile with a Si target. Previous molecular dynamics simulations demonstrate that this unusual behavior is due to the fact that strong covalent bonds are formed between the C atoms in the projectile and the Si atoms in the target, which result in the implantation of carbon into the solid. The focus of this paper is to understand how the formation of chemical bonds affects the net sputtered yield. The results of molecular dynamics simulations of the keV bombardment of Si with C₆₀, Ne₆₀ and ¹²Ne₆₀ at normal incidence are compared over a range of incident kinetic energies from 5 to 20 keV. The net yields with Ne₆₀ and ¹²Ne₆₀ are significantly greater than with C₆₀ at all incident kinetic energies, with ¹²Ne₆₀ having the largest values. Application of the mesoscale energy deposition footprint (MEDF) model shows that the initial deposition of energy into the substrate is similar with all three projectiles. Snapshots of the initial pathway of the projectile atoms through the substrate show a similar lateral and vertical distribution that is centered in the region of the energy footprint. Therefore, the reason for the reduced yield with C₆₀ is that the C atoms form bonds with the Si atoms, which causes them to remain in the substrate instead of being sputtered.     

Observation of a partially-ordered void lattice in aluminium irradiated with 400 keV Al+ ions

Transmission electron microscopy observations of voids formed in aluminium during irradiation at 50°C and 75°C with 400 keV Al⁺ ions, have shown that partially-ordered void arrays are often present. These arrays occur in high-purity annealed aluminium, which has been implanted with 10^?4 atom/atom helium before ion irradiation. The void concentration is found to be $\text{～3 × 10}{}^{16}\text{/ cm}{}^3$, and the void lattice parameter ～ 700 Å. The ratio of void lattice parameter to void radius is ～ 12. Ordered void lattices have been observed frequently in irradiated body-centred cubic metals but the only previous observation for a face-centred cubic metal was in nickel. Theoretical predictions of void lattices in metals are discussed and related to the observations reported herein.     

Reaction of molybdenum and molybdenum-base alloy with sintered Li2O pellets

The reaction of sintered lithium oxide (Li₂O) pellets with molybdenum and molybdenum-base alloy TZM has been studied in the temperature range 800–1100 °C for a constant reaction period of 100 h under a dynamic vacuum. The reaction proceeded measurably at about 950°C and appreciably above 1000°C. Metallographic and X-ray diffraction analyses indicated that a reaction product scale was formed at the interface and the scale consisted mainly of Li₄MoO₅. TZM showed slightly higher reactivity compared to molybdenum.     

Radiotoxicity hazard of U-free PuO2+ZrO2 and PuO2+ThO2 spent fuels in LWR

The radiotoxicity hazard of U-free Rock-like oxide: ROX (PuO₂+ZrO₂) and Thorium oxide: TOX (PuO₂+ThO₂) LWR spent fuels is investigated and radiotoxicity hazard of MOX spent fuel is considered as a reference case. The long-term ingestion radiotoxicity hazard of ROX spent fuel is one third and nearly one fourth of that of TOX and MOX spent fuels, respectively. This is because the discharged Pu and long lived Np in ROX fuel is less than that of TOX and MOX fuels. In TOX fuel, discharged Pu and MA are lower than that of MOX fuel but the long-term radiotoxicity hazard of spent fuel is nearly the same as MOX spent fuel. At the cooling 10⁵ years, the radiotoxicity hazard of TOX spent fuel is approximately ten and three times higher than that of ROX and MOX spent fuels, respectively due to higher toxic contribution of ²²⁹Th in TOX spent fuel.     

Thickness and MeV Si ions bombardment effects on the thermoelectric properties of Ce3Sb10 thin films

The three single layer Ce₃Sb₁₀ thin films were grown on silicon dioxide and quartz (suprasil) substrates with thicknesses of 297, 269 and 70 nm using ion beam assisted deposition (IBAD) technique. The high-energy cross plane Si ion bombardments with constant energy of 5 MeV have been performed with varying fluence from 1 × 10¹², 1 × 10¹³, 1 × 10¹⁴, 1 × 10¹⁵ ions/cm². The Si ions bombardment modified the thermoelectric properties of films as expected. The fluence and temperature dependence of cross plane thermoelectric parameters that are Seebeck coefficient, electrical and thermal conductivities were determined to evaluate the dimensionless figure of merit, ZT. Rutherford backscattering spectrometry (RBS) enabled us to determine the elemental composition of the deposited materials and layer thickness of each film.     

Populations of np terms in deuterium atoms emergent from carbon foils bombarded with D+, D2+ and D3+ ions

We have measured relative beam-foil populations of 2p, 3p, and 4p terms in D⁰ as a function of the projectile energy $\text{(20 ?}\text{E}\text{M}\text{? 500}\text{keV}\text{amu}\text{)}$ for D⁺, D₂⁺, and D₃⁺ ions impinging on carbon foils of various thicknesses (? 2–20 $\text{μg}\text{cm}{}^2$).With D⁺ projectiles, the np populations reach their equilibrium values even in the thinnest foils used. We compare the dependence on energy of these populations to the equilibrium neutral fraction variation for hydrogen (deuterium) beams emerging from a carbon foil and deduce some information concerning beam-foil populations.When molecular projectiles pass through very thin foils, well known molecular effects appear which depend on the dwell time, t, i.e., the time spent by the projectile in the foil. In this work we consider only the long-dwell-time region t > 2 × 10^?15s. We study the variation of R_α = I^molec/I^atom (I^molec and I^atom are the Ly-α intensities per incident deuteron (proton) observed with molecular and atomic projectiles of the same velocity, respectively) with the projectile energy per nucleon ($\text{E}\text{M}$) and the thickness (T) of the foil. For a foil of given thickness, R_α increases with $\text{E}\text{M>}$ and reaches a saturation value R_∞ which decreases when T increases. These results, in agreement with our previous measurements using hydrogen projectiles, indicate that t is not the only parameter relevant to molecular effects. Comparisons are reported between $\text{R>}{}_{\mathrm{\alpha }}\text{(E}\text{M>}$) values obtained (a) with H₂⁺ and D₂⁺ projectiles and (b) with D₂⁺ and D₃⁺ projectiles, using foils of various given thicknesses. Ratios $\text{R}{}_{\mathrm{\beta }}\text{(E}\text{M}$) and $\text{R}{}_{\mathrm{\gamma }}\text{(E}\text{M}$) are also measured using Ly-β and Ly-γ radiations and compared to $\text{R}{}_{\mathrm{\alpha }}\text{(E}\text{M}$) values. An interpretation for some of our results is proposed.     

Li4SiO4 pebbles reduction in He + 0.1% H2 purge gas and effects on tritium release properties

Lithium orthosilicate reduction was examined by Temperature Programmed Reaction (TPR) and Temperature Programmed Desorption (TPD) methods performed in He (or Ar) + H₂ purge gas flowing through pebble bed specimens. The parameters governing the kinetics and the steady-state of the reduction process to Li₄SiO_4−x were determined at 800°C. The level x of the O-vacancy concentration at steady-state (of the order of 1.5×10⁻³ mole fraction) was found to be compatible with the impurities content in the specimens. Pebble pre-annealing treatments were found to affect the microstructure and the reduction mechanism. Post-irradiation tritium release by TPD tests were performed on both stoichiometric and reduced pebbles with similar results. Tritium release properties of this breeder system seem to be independent from the material reduction state (x).     

The surface tension effects in boiling heat transfer of cryogenic LN2 on an ellipsoid

The study researched into a simple theoretical model for turbulent film boiling heat transfer on an ellipsoid with influence of surface tension. It begins from assuming an isothermal ellipsoid immersed in the stagnant saturated liquid. The effects of non-linear thermal conductivity, absolute viscosity, and the eddy diffusivity in the vapor film are all included in this paper. The results show, for higher eccentricity values, the eccentricity and the surface tension have some slight influence on the mean Nusselt. However, for lower eccentricity values, the influence of eccentricity and surface tension effects on the mean Nusselt can almost be neglected. Finally, a comparison between the results of the present study and those reported in previous theoretical and experimental studies is provided. And the results were found in a good agreement with the previous data.     

Study on effects of swift heavy ion irradiation on the crystal structure in CeO2 doped with Gd2O3

To simulate the effects of Gd₂O₃-doping and high-energy fission products in UO₂, Gd₂O₃-doped CeO₂ pellets were irradiated with 200-MeV Xe¹⁴⁺ ions. Doping and irradiation effects were analyzed using X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS). The lattice constant of CeO₂ decreases and the local structure is disordered with increased doping levels. However, the irradiation induces an expansion of the lattice and a disordering of atomic arrangement near the Gd atoms. The effects of the irradiation become more pronounced with increasing Gd₂O₃-dopant levels. Our results are compared with those of a study involving Er₂O₃-doped CeO₂.     

An experimental study on linear differential scattering coefficients of the radioactive compounds UO2(C2H3O2)2 · 2H2O and Th(NO3)4 · 5H2O at 60 keV

The linear differential scattering coefficients at 60 keV have been measured for UO₂(C₂H₃O₂)₂ · 2H₂O (uranyl-acetate) and Th(NO₃)₄ · 5H₂O (thorium-nitrate) radioactive compounds at seven angles ranging from 60° to 120° at intervals 10°. The obtained results have been compared with relativistic and non-relativistic theoretical values.     

Experimental cross sections for two-electron capture into nitrogen autoionising states in Nq+ (q = 6, 7) on He and H2 collisions at 10.5q keV

Singly differential cross sections for two-electron capture into autoionising states (nl, n'l') with n = 2, 3, 4 and n′≥ in N^q+ (q = 6, 7) on He and H₂ collisions have been measured at 10.5q keV collision energy and an observation angle θ_lab =11.6°Total cross sections are estimated assuming isotropic angular distributions.     

Gamma irradiation effects on ZnO-based scintillating glasses containing CeO2 and/or TiO2

Irradiation resistance of as-studied scintillating glass samples were tested under the ⁶⁰Co γ-ray radiation at doses between 60 and 700 Gy. Photoluminescence properties of glasses with and without cerium ions were investigated to show the effect of cerium (III) on the luminescence of ZnO. Ultraviolet and visible optical transmittance spectra were compared before and after irradiation treatment. The so-called radiation-induced absorption coefficient (RIAC) was introduced to compare more effectively the radiation damage on glass samples. The much reduced transmittance change and decreased RIAC value in UV-Vis region indicate that the density of electron centers and hole centers caused by radiation decreased, which helps to confirm that the reduction and oxidation reaction of cerium ions took place in radiation process. From RIAC curves, it can be seen that TiO₂ enhances the irradiation resistance of sample in UV region. However, high TiO₂ content has negative effect on visible transmittance of glasses after the higher dose irradiation (700 Gy).