中子福照硅单晶正电子捕获的温度效应

用正电子湮没寿命测量方法研究了在中子辐照硅单晶缺陷中正电子捕获的温度效应。寿命谱被成功地分成两个组分,长寿命组分在109—300K的温度范围有325±9 ps的常数寿命值,它被认为是在负荷电双空位捕获的正电子寿命。正电子捕获率显示一个强的负温度效应.这个捕获特征能用正电子在负荷电双空位的级联捕获来描述。在低温区正电子捕获截面以T~(-1.7)随温度变化。     

Temperature dependence of liquid Sn sputtering by low-energy He and D bombardment

Absolute sputtering yields of liquid tin from 240 to 420 °C due to irradiation by low-energy helium and deuterium have been measured. For ion energies ranging from 300 to 1000 eV, temperature enhancement of liquid tin sputtering was noted. These measurements were obtained by IIAX (the Ion-surface InterAction eXperiment) using a velocity-filtered ion beam at 45° incidence to sputter material from a liquid tin target onto deposition monitors. Sputtering yields from 500 eV ion bombardment at 45° incidence increase from 0.1 ± 0.03 and 0.019 ± 0.008 Sn particles/ion at room temperature, for He⁺ and D⁺ ions respectively, to 0.30 ± 0.12 and 0.125 ± 0.05 Sn particles/ion for 380 °C. Temperature enhanced sputtering has been seen in other liquid metals (namely lithium, tin-lithium, and gallium) using both ion beam and plasma irradiation.     

Temperature dependence of trapping and depth profiles of 6 to 15 kev deuterium in carbon

Depth profiles of 30 keV D⁺₂ and 20 keV D⁺₂ implanted into edge and basal-oriented pyrolytic graphite have been measured by means of the D(³He,α)H nuclear reaction in the temperature range of 300 to 800 K. At room temperature deuterium concentrations up to 30 at.% are found in a surface layer corresponding to the range of the ions. The measured depth profiles do not fully agree either with calculated range profiles or with the damage profiles, but are determined by the two together. At higher temperatures the deuterium concentrations decrease and the profiles broaden. At room temperature the amount of trapped deuterium increases linearly with dose below 10¹⁸ deuterons/cm². The trapping coefficient is roughly 60%. At 5 × 10¹⁸ deuterons/cm² the amount of trapped deuterium in the probed layer (~4000 Å) reaches saturation and the trapping coefficient becomes zero. The saturation value decreases with increasing temperature and increases with increasing energy.     

Temperature dependence of erosion of alloys of vanadium and niobium during bombardment with helium ions

Conclusions It has been established that maximal erosion of vanadium and its alloys is observed at 700–900°K, the corresponding range for niobium alloys being 900–1100°K. The maximal value of the erosion coefficients of alloys for vanadium and alloys V+25% Zr+C, Nb+4.2% Mo+Zr, and Nb+1.1% Zr+C is 1.5±0.7, 0.6±0.3, 0.4±0.2, and 0.15±0.07, respectively.Translated from Atomnaya Énergiya, Vol. 42, No. 1, pp. 13–15, January, 1977.     

Enhanced hydrogen trapping due to He ion damage

Single crystals and rolled foil of Mo with and without predamage by 11 or 18 keV⁴ He at room temperature have been injected with 8 or 16 keV H and D isotopes. The H depth profiles and the total D retention were measured by nuclear microanalysis techniques. A strong enhancement in the trapping of hydrogen isotopes after He predamage over Mo without predamage is observed and the H depth profiles scale with the He ion energy. Cold work increases the D trapping in the absence of He damage but after 3 × 10¹⁵ He/cm² predamage little difference remains in the total trapping for single crystals and rolled foil. The release of the D upon annealing due to detrapping occurs primarily between 100 and 450°C. A similar fractional reduction in trapping is observed for elevated temperature D injection as is found in the anneal to corresponding temperatures of room temperature injected samples.     

Absorption and outgassing of helium during He+ ion bombardment of niobium

Conclusions The capute and outgassin of helium during bombardment by He⁺ ions of energy up to 15 KeV of a niobium target witha temperature of 290–1800°K have been studdied. It has been shown that as the temperature during irradation, T_b, is increased the coefficient of gaseous emission, , increases, while the number of injected atoms, N₀, and the capture coefficient decrease. For temperature greater than 1500°K practically 100% of the bombarding atoms are released to the vacuum. As the dose is increased, and N₀ increase and falls. An increase in to unity indicates saturation of saturation of theniobium by helium. The irradiation dose at which this saturation sets in and its level decrease with the temperature T_b.As a result of an analysis of the outgassing spectra, it has been shown thatthe release of helium occurs in three stages, each of which is due to one of the following causes: diffusion of individual atoms dissolved in the lattice; relase of helium from gas bubbles located in the volume of the metal; release of gas due to bursting of the shells of surface blisters. The last process has a basic role in outgassing at large irradiation doses.Translated from Atomnaya Énergiya, Vol. 38, No. 3, pp. 152–155, March, 1975.     

Theory of He trapping, diffusion, and clustering in UO2

We have performed ab initio total energy calculations to investigate the behavior of helium and its diffusion properties in uranium dioxide (UO₂). Our investigations are based on the density functional theory within the generalized gradient approximation (GGA). The trapping behavior of He in UO₂ has been modeled with a supercell containing 96-atoms as well as uranium and oxygen vacancy trapping sites. The calculated incorporation energies show that for He a uranium vacancy is more stable than an oxygen vacancy or an octahedral interstitial site (OIS). Interstitial site hopping is found to be the rate-determining mechanism of the He diffusion process and the corresponding migration energy is computed as 2.79 eV at 0 K (with the spin-orbit coupling (SOC) included), and as 2.09 eV by using the thermally expanded lattice parameter of UO₂ at 1200 K, which is relatively close to the experimental value of 2.0 eV. The lattice expansion coefficient of He-induced swelling of UO₂ is calculated as 9 × 10⁻². For two He atoms, we have found that they form a dumbbell configuration if they are close enough to each other, and that the lattice expansion induced by a dumbbell is larger than by two distant interstitial He atoms. The clustering tendency of He has been studied for small clusters of up to six He atoms. We find that He strongly tends to cluster in the vicinity of an OIS, and that the collective action of the He atoms is sufficient to spontaneously create additional point defects around the He cluster in the UO₂ lattice.     

Temperature dependence of dislocation bias factors in metals

Recently, it has been shown that edge dislocations are not stable sinks for vacancies. Trapping and detrapping of vacancies occur as a thermally-activated process. In this paper, the temperature dependence of vacancy absorption coefficient of edge dislocations under irradiation was calculated by using rate equations in Fe and Ni. The temperature dependence was almost the same in both Fe and Ni and did not depend on the damage rate between 10⁻¹⁰ dpa/s and 10⁻⁶ dpa/s. At low temperatures such as room temperature, the coefficient was low and with increasing irradiation temperatures, it had a peak (500 K) and decreased.     

Temperature dependence of the zircaloy-4 strength-differential

An investigation was undertaken to determine the behavior of the strength-differential in the three principal directions of α-rolled, Zircaloy-4 plate as a function of temperature. The method of using Knoop hardness numbers to generate yield loci was employed in determining the magnitude of the strength-differential. It was found that the magnitude of the strength-differential was proportional to the concentration of basal poles along the direction of consideration and that it decreased in magnitude with increasing temperature. However, it remained of significant magnitude (≈85 MPa) in both the transverse and normal directions at light water reactor operating temperatures. Use of the elevated temperature, strength-differential data in clad creep down analyses demonstrated that the consideration of the strength-differential in clad creep analysis can increase predicted collapse times by a factor greater than two in pressurized water reactor fuel pins. It was also found that the strength-differential effect on such predictions is sensitive to clad texture.     

Temperature dependence of sputtering behavior of Cu-Li alloys

Three different Cu-Li alloys (4, 10, and 16% Li) have been sputtered by 1 keV and 100 eV D⁺ ions. The Cu sputtering yield and the total weight loss was measured as a function of the target temperature between 25 and 700°C. The yield was measured by the catcher foil technique and by the weight loss method in order to differentiate between the total weight loss and the Cu sputtering yield (i.e., Rutherford backscattering analysis (RBS) of the catcher foil). Targets with lower Li concentration (4 and 10%) did not show a significant change of the Cu sputtering yield [1] as found by other authors [2] and this is probably due to the higher current density (10¹⁵ cm⁻² s⁻¹) in this experiment. An increase in weight loss at temepratures above 550°C was caused by Li evaporation. The target with high Li concentration (16% Li) showed a reduction of the Cu sputtering yield by more than a factor of 50 for both the 1 keV and the 100 eV D⁺ ions. This reduction occurs in a small temperature range around 550°C, which coincides with the transition on the Cu-Li phase diagram from the a-phase to α + liquid. For temperatures above 550°C the sputtering yield increases again, most probaby due to an enhanced evaporation of Li. At optimum temperature conditions, the evaporation rate of Li for the Cu-Li alloy is many orders of magnitude lower than the rate for pure Li. According to the phase diagram, the Cu-Li alloy with even higher Li concentration could reach optimum conditions at lower temperatures and, therefore, would be a promising first-wall candidate.     

The Effect of High Temperature He+ Implantation on Polycrystalline Tungsten in IR-IECF

High temperature (1,100–1,200°C) implantation impact of helium ions in PC Tungsten as a candidate fusion first wall material was studied in the Iranian Inertial Electrostatic Confinement device (IR-IECF). High energetic (100–120?keV) helium ions were applied to produce fluences up to 5?×?10²⁰ He⁺/cm² on the surface of Tungsten. Scanning electron microscopy (SEM) was used to investigate surface morphology changes for various ion fluences. The results showed formation of ‘coral-like’ surface structure and exfoliation and intensive increment in pore formation at high fluence. Microhardness measurements were used to evaluate mechanical properties of implanted tungsten. These investigations revealed that hardness increased with greater He⁺ dose. The phase formation and structural evolution were studied by X-ray diffractometry method.     

Temperature dependence of damage formation in Ag ion irradiated 4H-SiC

Rutherford backscattering spectrometry (RBS) in channelling mode was used to study the defect formation in silver (Ag) ion irradiated silicon carbide (SiC). The 4H-SiC samples were irradiated with 360 keV Ag ions at different temperatures (15, 295, 375, 475, 625 and 875 K) over a wide range of fluences (1×10¹¹ to , depending on the irradiation temperature). The results can be divided into two groups: (i) for irradiation temperatures between 15 and 475 K amorphisation of the implanted layers is reached for ion fluences between 7×10¹³ and . The over-all cross-section of defect production at very low ion fluences which comprises the formation of point defects and of amorphous clusters, is almost identical for all data sets measured in this temperature range. Differences in the damage evolution which occur at higher ion fluences, suggest that the relative contribution of amorphous clusters within single ion impacts in crystalline material decreases with rising temperature. (ii) For irradiations performed at 625 and 875 K no amorphisation is found for ion fluences as high as . With increasing ion fluence the defect concentration exhibits a distinctive plateau due to the balance between formation and recombination of point defects before increasing up to a saturation level well below amorphisation. For this final stage our results indicate a mixture of point defect clusters and extended defects most probably dislocations. A comparison with data from the literature suggests that the damage evolution for implantation at 625 and 875 K is strongly influenced by the mobility of vacancies starting at around 600 K.