The onset of radiation blistering as a function of target temperature for D+ irradiated copper

Radiation blistering in 200 keV D⁺ irradiated copper has been studied for target temperatures in the range 120 to 380 K. Abrupt changes in both the critical dose for blistering and the blister morphology are observed to occur at target temperatures of 195 ± 10 and 300 ± 5 K. For target temperatures in the ranges 120 to 190 K and 300 to 380 K, semi-spherical blisters with a mean diameter of ~5.5 μm are observed to form at fluences of $\text{(2.0 ± 0.5) × 10}{}^{22}$ and $\text{(4 ± 1) × 10}{}^{22}\text{d/m}{}^2$, respectively. In the intermediate temperature region, irregularly shaped blisters with a mean diameter of ~1.3 μm are found to form at a fluence of $\text{(6 ± 2) × 10}{}^{21}\text{d/m}{}^2$. Depth profiles of the implanted deuterium have been obtained. The deuterium concentrations at the onset of blistering are found to be approximately constant over the temperature ranges 120 to 190 K and 190 to 300 K, although a different concentration is observed in each range. For temperatures above 300 K, the deuterium concentration at the onset of blistering is found to decrease with increasing temperature.     

Dose and microstructural effects on surface topography change and sputtering yield in polycrystalline molybdenum bombardment with 2 keV Ne+ions

The topographic change and sputtering yield in polycrystalline molybdenum due to the bombardment with normally incident 2 keV Ne⁺ ions have been investigated to study dose and microstructural effects at room temperature in three differently fabricated molybdenum samples. The surface topography changes with increasing dose and depends on the microstructure of the samples. The cones were formed at a dose above $\text{4 × 10}{}^{18}\text{ions/cm}{}^2$, and the number density and height of the cone increased with increasing dose. The distribution of cones was localized, and the aggregation of impurities including implanted neon atoms on cones was not observed. The sputtering yields in the three molybdenum samples were found to be the same value ($\text{0.90 ± 0.10}$) atoms/ion for 2 keV Ne⁺ ions, in spite of different surface topography changes caused by sputtering.     

Sputtering of silicon carbide coatings by low-energy hydrogen ions

Various types of silicon carbide coatings made by reactive ion-plating have been bombarded with a 3.0 keV H⁺₃ ion beam at temperatures around 500°C. The sputtering yield in stoichiometric samples (i.e. Si : C = 1 : 1) at 500°C was $\text{1.15 × 10}{}^{\mathrm{?2}}$ atoms/H⁺. As the stoichiometry deviates from this point, the sputtering yield has larger values. The temperature dependence of the sputtering yield in stoichiometric samples was negligible below 600°C. No surface topography changes occurred in stoichiometric samples even at a high fluence of $\text{2 × 10}{}^{20}\text{H}{}^{\mathrm{+}}\text{/cm}{}^2$, while severe erosion took place in non-stoichiometric samples. By Auger electron spectroscopy (AES), carbon exists on the surface in the form of carbide in stoichiometric SiC before and after bombardment, while it exists in the form of graphite in carbon rich samples, which suggests that the bound state of carbon in the form of carbide should correspond to the low sputtering yield in stoichiometric SiC coatings. The surface stoichiometry changes due to hydrogen bombardment were observed by AES, where the carbon population increases in stoichiometric SiC, while it decreases in carbon rich samples, which was supported as well by the results from electron probe X-ray microanalysis.     

Surface deformations and gas escape process studied by quasi-simultaneous multiple-energy He irradiation

Single crystal silicon wafer covered by Al foil of thickness 5 μm was irradiated quasi-simultaneously by multiple-energy He ions up to the fluence level of $\text{3.3 × 10}{}^{19}$ ions/cm². The implantation was performed by 3.5 MeV ⁴He⁺ through a moving Al absorber foil in such a way that a nearly uniform He distribution was obtained extending in both Si and Al to depth intervals of $\text{1.9 × 10}{}^{19}$ Si/cm² and of $\text{1.5 × 10}{}^{19}$ Al/cm², respectively. During irradiation the evolution of the He concentration-depth profile was studied in situ by 3 MeV proton RBS analysis. It was found that the He concentration in the Al cover foil, after reaching a maximum value of 30 at.% began to decrease. This accelerated re-emission process was initiated near the inter-boundary surface and extended inward gradually. No significant He escape was observed from the Si up to the applied dose, so at the end of the implantation a He concentraton of 80 at.% has been reached.Exposing both inter-boundary surfaces to SEM, flaking from numerous spots was observed on the Al but not on the Si where only one crater was found. After mechanically breaking the implanted Si wafer and Al cover foil it could be seen on the fracture surfaces that regions containing a large amount of He acquire a sponge-like structure. Channels and large cavities were also observed in this region of the broken Si produced as cracks of interconnected He bubbles. The appearance of the flaking processes clearly demonstrates that even with such a depth distribution the He implanted in the materials in spite of re-emission may reach the critical value for blistering or flaking. The critical concentrations required for the observed surface deformation together with the thickness of the flaked layers evaluated from RBS and SEM observations are discussed.     

Neutron sputtering of gold

The sputtering yield of gold bombarded with fission neutrons was studied in the CP-5 reactor. The experiment was designed to investigate sputtering patterns in addition to the sputtering yield. The investigation was carried out on bulk single crystals and near liquid helium temperature. Overall sputtering yields ranged from $\text{1 × 10}{}^{\mathrm{?3}}\text{to}\text{6 × 10}{}^{\mathrm{?3}}$ sputtered gold atoms per incident neutron for doses ranging from $\text{2.1 × 10}{}^{17}\text{to}\text{5.5 × 10}{}^{17}\text{(}\text{nvt > 0.1 MeV}\text{)}$. These results are roughly an order of magnitude larger than many previously reported sputtering yields. Sputtering patterns have not been pursued yet, due to prohibitively high background radiation.     

Fission-enhanced self-diffusion of uranium in UO2 and UC

In-pile self-diffusion measurements in stoichiometric UO₂ sinters and single crystals and in arc-cast stoichiometric UC have been performed using the thin layer condition and ²³³U as tracer. The nominal irradiation temperature was 900°C. The resulting diffusion coefficients $\text{D1}$ of $\text{1.5 × 10}{}^{\mathrm{?16}}\text{cm}{}^2\text{· sec}{}^{\mathrm{?1}}$ for UO₂ and $\text{2.2 × 10}{}^{\mathrm{?17}}\text{cm}{}^2\text{· sec}{}^{\mathrm{?1}}$ for UC for a fission rate $\text{S}$ of 1 × 10¹³f/cm³ · sec represent radiation enhanced diffusion and are higher by factors of 10³ to 10⁴ than (extrapolated) coefficients of thermal diffusion. The data are of immediate relevance for understanding and predicting such important quantities as in-pile sintering and densification, diffusion controlled creep and fission gas behavior in the outer zones of the fuel. They are at the upper limit of expected values.     

A new technique for measuring sputtering yields at high energies

The use of thin, self-supporting carbon catcher foils allows one to measure sputtering yields in a broad range of materials with high sensitivity. Analyzing the foils with Rutherford forward scattering, we have measured sputtered A1, Si and P surface densities down to 5 × $\text{10}{}^{13}\text{cm}{}^2$ with uncertainties of about 20%.     

Measurement of chemical sputtering yields of various types of carbon

Measurements of the chemical sputtering during the bombardment of pyrolytic graphite, isotropic carbon and glassy carbon with 0.1–6 keV hydrogen ions have been made in the temperature rarige of room temperature to 700°C. The maximum production rate occurs at 1 keV for the incident energy and 525°C for the target temperature in all types of carbon. Energy and temperature dependences of chemical sputtering of carbon are not affected by the structures of the carbon. The reason is ascribed to radiation damage of the surface of the carbon. The dose dependence of the methane production rate was influenced by the hydrogen concentration in a target prior to bombardment, but the steady rate was obtained after the target was bombarded with protons at a dose of more than $\text{1 × 10}{}^{18}\text{H}{}^{\mathrm{+}}\text{/cm}{}^2$.     

The oxygen snoek damping and an abnormal peak of neutron-irradiated vanadium

Measurements of low-frequency internal friction and electron microscope observations were made on neutron-irradiated vanadium with various oxygen contents. Irradiation was carried out at about 60°C to a fast fluence of $\text{2 × 10}{}^{17}$ or $\text{5 × 10}{}^{19}$ n/cm² ($\text{E ? 1 MeV}$). The oxygen Snoek damping was decreased by irradiation and post-irradiation annealing below 200 or 250° C, while it began to recover by annealing above this temperature. Complete recovery was attained by 30 min anneal at 450°C in the case of the lower fluence, whereas in the other case it was not observed after the same treatment. The results of electron microscope observations were consistent with those of internal friction measurements. The specimens irradiated to $\text{5 × 10}{}^{19}$ n/cm² showed an abnormal peak after annealing above 250°C near the nitrogen Snoek temperature. The height of this peak, $\text{P}{}^{\mathrm{?1}}{}_{\mathrm{<mtext>max</mtext>}}$, was expressed as $\text{P}{}^{\mathrm{?1}}{}_{\mathrm{<mtext>max</mtext>}}$ ∝ exp ($\text{2.72 × 10}{}^3\text{/RT}$) $\text{Q}{}^{\mathrm{?1}}{}_{\mathrm{<mtext>max</mtext>}}$, where $\text{Q}{}^{\mathrm{?1}}{}_{\mathrm{<mtext>max</mtext>}}$ the heiβht of the oxygen Snoek damping after each annealing. The mechanism for radiation-anneal hardening and the abnormal peak were considered in the light of these experiments.     

Neutron irradiation effects on the mechanical properties of organic composite materials

Neutron irradiations with low γ-ray flux in the Intense Pulsed Neutron Source were carried out on four kinds of cloth-filled organic composites (filler: E-glass or carbon fiber; matrix: epoxy or polyimide resin) and a unidirectional alumina fiber/epoxy composite. These composites were examined with regard to the mechanical properties at room temperature. Following irradiation at room temperature, the Young's (tensile) modulus of these composites remains practically unchanged up to a total neutron fluence of $\text{5.0 × 10}{}^{18}\text{n/cm}{}^2$ ($\text{1.4 × 10}{}^{18}\text{n/cm}{}^2$ for $\text{E > 0.1 MeV}$). The shear modulus and the ultimate strength, on the other hand, decrease significantly at this neutron fluence for the glass/epoxy and glass/polyimide composites, whereas for the other composites both properties do not degrade. This result is most likely ascribed to the radiation damage at fiber/matrix interface due to recoil particles produced by a ${}^{10}\text{B(n,α)}{}^7$ Li reaction in the boron-containing E-glass fibers. Only for the E-glass fiber composites, in fact, the fracture propagation energy is appreciably increased by irradiation, while for the other composites the propagation energy is scarcely changed, thus confirming the significant contribution due to the ¹⁰B reaction. As to the 5 K irradiation, degradation of the present composites was not observed up to a total neutron fluence of $\text{1.0 × 10}{}^{18}\text{n/cm}{}^2$ ($\text{7.0 × 10}{}^{17}\text{n/cm}{}^2$ for $\text{E > 0.1}\text{MeV}$) when tested at room temperature.     

Neutron irradiation effects in uranium dicarbides

Changes of electrical resistivity and lattice parameter in UC_1.96 after neutron irradiation from $\text{9 × 10}{}^{14}$ to $\text{2 × 10}{}^{18}$ nvt were studied. The resistivity was increased with the dose up to $\text{1 × 10}{}^7$ nvt, and saturated at that dose. Above 10¹⁸ nvt a steep increase was observed. In the lattice-parameter changes, on the other hand, a gradual increase was observed in the dose range between $\text{2 × 10}{}^{16}$ and $\text{8 × 10}{}^{17}$ nvt; above that dose, an abrupt increase followed. Annealing experiments on the resistivity were performed up to 1000°C using the specimens irradiated to the low dose of $\text{5 × 10}{}^{16}$ nvt, and the increased resistivity was completely recovered in three steps. The activation energies of each step were estimated to be 0.3, 0.5 and $\text{1.6 ± 0.2}$ eV.     

Radiation and anneal hardening in neutron-irradiated vanadium

Vanadium samples were neutron irradiated at the reactor ambient temperature to fluences in the range from 2.0 × 10⁷ to 1.0 × 10²⁰ n/cm² ($\text{E}{}_{\mathrm{n}}\text{? 1 MeV}$). The radiation hardening measured at the ambient temperature increased linearly with the square root of the neutron fluence, up to a fluence of about 2.5 × 10¹⁹ n/cm², to approximately $\text{25 kg/mm}{}^2$ for the highest fluence. The radiation-anneal hardening phenomenon was clearly observed in samples irradiated at a low fluence (2.0 × 10¹⁷ and 1.0 × 10¹⁸ n/cm²) and the hardening was accompanied by changes in the density and size distribution of the radiation-produced defect clusters. The radiation hardening induced during irradiation to 1.0 × 10²⁰ n/cm² recovered monotonically as the annealing temperature increased. Defect clusters invisible in the electron microscope played an important role in the radiation and anneal hardening except when radiation hardening was induced at the highest fluence.     

Influence de la dose de neutrons rapides sur la formation des cavites dans l'aluminium

The results of neutron irradiation of aluminium at 55°C under a fast flux of $\text{(1.4 ± 0.2) 10}{}^{14}\text{n · cm}{}^{\mathrm{?2}}\text{· sec}{}^{\mathrm{?1}}$ to doses ranging between 10¹⁹ and $\text{3 × 10}{}^{21}\text{n · cm}{}^{\mathrm{?2}}$ are presented. Experimental observations suggest that dislocations play an important role in void nucleation and growth. Monte-Carlo calculations of void growth in the presence of a dislocation describe reasonably well the experimental results.     

The diffusion of fission products in thorium metal

A study was performed of the diffusion in α-thorium of fission products representing impurity atoms with a diversity of size and valance differences with respect to the solvent lattice. The atoms were recoil injected into thorium disks. Diffusion coefficients were determined for ¹³³Xe by monitoring its release during annealing, and for the other isotopes by post-annealing concentration profile analysis. The Arrhenius constants $\text{d}{}_{\mathrm{o}}\text{(cm}{}^2\text{/sec)}$, resp. $\text{Q(kcal/mole)}$ were obtained for the diffusion coefficients where. $\text{D = D}{}_{\mathrm{o}}$exp$\text{(?Q/RT)}$;${}^{99}\text{Mo: 7.6 × 10}{}^{\mathrm{?4}}$ and $\text{37.6;}{}^{132}\text{Te: 1.32 × 10}{}^6$ and $\text{95.6;}{}^{133}\text{I: 2.7 × 10}{}^{\mathrm{?1}}$ and $\text{66.2;}{}^{133}\text{Xe: 3.6 × 10}{}^2$ and $\text{82.3;}{}^{140}\text{Ba: 2.3 × 10}{}^{\mathrm{?2}}$ and $\text{59.4;}{}^{141}\text{Ce ?}{}^{143}\text{Ce: 1.8 × 10}{}^{\mathrm{?2}}$ and 60.0. The fission product diffusion behavior, in general, fit either the vacancy or the substitutional-interstitial diffusion mechanisms for impurity atoms in a fcc metal. Both valence and ionic radius correlations were found. The data indicate low rates of diffusion for the operating temperatures at which α-thorium-based fuel might be used.     

Fluage du pyrocarbone sous irradiation

Three massive samples of pyrocarbon were irradiated at 1100°C for a maximum fast-neutron dose of $\text{1.6 × 10}{}^{21}$ DNE. They were subjected to stresses in the range $\text{1.33 × 10}{}^2\text{–2 × 10}{}^2$ Kg/cm². The pyrocarbon was deposited from methane in a rotating furnace. Its density, its isotropy, its structure according to X-rays and TEM relate closely to its homologue deposited from methane in fluidised conditions. A study of creep under irradiation showed that a brief stage of primary creep is followed by a stage which is linear with respect to both stress and fast-neutron dose. Creep is thus well represented by an expression of the form $\text{? = Kσφ}$, where $\text{K}$ is $\text{2 × 10}{}^{\mathrm{?25}}$ (Kg · cm^?2. DNE)^?1, which is a value ten times greater than previously estimated. Irradiation is accompanied by densification, a slight increase in anisotropy and a reduction in $\text{L}{}_{\mathrm{c}}$ (apparent crystallite size measured along the $\text{c}$ axis). The variation of these parameters with dose does not, however, differ appreciably between the three creep samples and the unstressed sample.     

Light ion bombardment sputtering,stress buildup,and enhanced surface contamination

Several effects of high fluence light ion bombardment which are relevant to fusion reactor inner wall problems are under investigation. The impurity loading and lateral stress from high fluence ion bombardments can alter sputtering yields markedly. This is demonstrated with sputtering measurements of 45 keV Kr incident upon Au. Sputtering yields for 150 keV⁴ He onto Au are presented for two different background hydrocarbon partial pressures during bombardment. It is shown that there is a polymerized hydrocarbon buildup on the surface for hydrocarbon partial pressures greater than $\text{1 × 10}{}^{\mathrm{?10}}\text{mm Hg}$ even for ion current densities ranging as high as 4 μA/cm²; true sputtering of the Au has been observed only for lower hydrocarbon partial pressures. Additional effects of oxidizing background gases on sputtering measurements of reactive metals are discussed.It is concluded that the background gas partial pressures, temperatures, and particle fluxes in a fusion device and in simulation experiments must be well defined before sputtering effects can be understood.     

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.     

Effect of cyclotron-injected helium on void-formation characteristics of type 304 stainless steel

Samples of Type 304 stainless steel were injected with helium by cyclotron bombardment to concentrations ranging between $\text{1.1 × 10}{}^{\mathrm{?7}}$ and $\text{1 × 10}{}^{\mathrm{?4}}$ ppma. Following cyclotron injection, the samples were given a variety of heat treatments prior to insertion in EBR-II for irradiation at 450 °C to a total dose of $\text{1 × 10}{}^{21}\text{n/cm}{}^2$. Samples that were not heat treated or that were annealed at 650 °C following cyclotron injection formed few voids and dislocation loops after EBR-II irradiation. This behavior is apparently due to the precipitate clusters that were formed during the helium injection. These precipitates were analyzed by electron microscopic techniques and found to have spherically symmetric strain fields that were of interstitial character. Samples that were annealed at 760 °C following cyclotron injection formed a larger number density of both voids and dislocation loops than did the control sample after EBR-II irradiation. The void volume also exceeded that of the control. Clustering of the dislocation loop population near grain boundaries and precipitate particles was observed in the control and low helium concentration samples.     

Lattice diffusion coefficient of oxygen in lithium oxide

Lattice diffusion coefficients of the oxygen ion in antifluorite-cubic Li₂O were determined employing polycrystalline samples, in the temperature range of 920 ~ 1130°C, by means of the gas-solid isotope exchange and solid-phase analysis technique; use was made of the relationship between the particle-size and grain-size dependences of the grain-boundary enhanced diffusion. The results were described by D = 1.52 × 10³ exp$\text{(?83.3 × 10}{}^3\text{/RT)}\text{cm}{}^2\text{s}$ and showed a good agreement with the previously reported results determined by the gas-phase analysis technique. Diffusion characteristics of the constituent ions in the antifluorite-cubic structure were discussed in comparison with those in fluorite-cubic crystals.