Stage II recovery of thermal neutron irradiated copper

Recovery stages at 65 K, 125 K and 220 K are discussed. The 220 K stage which seems to shift to lower temperature with increasing dose could be resolved into two substages at ～200 K and 220 K with dose dependent relative heights.     

Measurement of stored energy of KCl after 4·6°K reactor irradiation

Five KCl single crystals were irradiated at 4·6°K in the core of the Munich Nuclear Reactor for periods of 100 sec, 10 min, 1 hr or 10 hr, respectively. After irradiation the stored energy of the samples was measured in a differential-heat-flow calorimeter at two different heating rates: 0·29 and 1·1°K/min. At 0·29°K/min peaks of stored energy release were resolved at 21°K, near 27·5°K, at 32·5°K, at 42·5°K and near 50°K. An attempt was made to evaluate the corresponding activation energies using two different methods (see Table 1 in the text). The annealing stages at 21 and 32·5°K correspond to first order kinetics. The annealing stages at 42·5 and near 50°K are not of first order. A similar experiment was performed on KBr single crystals and is reported in the preceding paper. The results are compared with annealing studies on low temperature X-irradiated KCl and KBr crystals. From both our experiments it follows that also during reactor irradiation at 4·6°K ionization mechanisms of defect production should be responsible for the four observed low temperature recovery peaks; only defect recovery at higher temperatures may be at least partially explained by recombination of collision produced defects, i.e. the typical neutron irradiation effect as it takes place in metals.     

Ultrasonic detection of the pinning of dislocations by point defects in lead-I determination of migration energies

The ultrasonic attenuation of a γ-irradiated, deformed, single-crystal of lead has been measured between 77 and 270 K. Constant heating rate and isothermal anneals after low temperature irradiation yielded two dislocation pinning stages centered at 140 and 200 K and two dislocation depinning stages centered about 170 and 250 K. For an unirradiated sample one pinning stage centered at 170 and one depinning stage centered at 250 K were observed. Activation energies were calculated from isothermal anneals using an eigenfunction expansion model to be 0·16±0·04 and 0·36±0·05 eV for the pinning stages in the irradiated crystal and 0·28±0·05 eV for the pinning stage in the unirradiated crystal. The activation energy calculated from the same isothermal anneals using a Cottrell-Bilby analysis was 0·23±0·03 eV for the low temperature pinning stage in the irradiated crystal. The other activation energies were not changed. The discrepancy is discussed in Part II.     

Positron annihilation in the quenched and electron-irradiated NiSb intermetallic compound

Samples of the near equiatomic NiSb compound were irradiated by 3 MeV electrons at 20 K or quenched from 1103 K and 1333 K and subsequently annealed isochronally. The behaviour of defects created by quench or irradiation were studied by the positron annihilation technique. Only one recovery stage was found around 425 K for quenched specimens, but two distinct stages (100 K and 425 K) were observed after irradiation. The 425 K stage is ascribed to the migration of Ni vacancies giving dislocation loops. The recombination of mobile interstitials with vacancies after irradiation is assumed to occur between 100 K and 250 K. Doppler broadening and lifetime variations of positrons as a function of the measuring temperature in these irradiation samples are discussed.     

Multiple Phase Transitions in CuO Studied by μSR

Precise measurements of the local magnetic field at muon sites in CuO were performed. The temperature dependence of the local field including spatial orientation was obtained in the ordered state. Not only zero field μSR measurements were performed, but also external magnetic fields were applied to obtain an unambiguous determination of field direction. Multiple stages of muon signals were observed at 55 and 80 K. An incommensurate phase between 212 K and 227 K was confirmed from the line shapes of the local fields at the muon sites. This revised version was published online in September 2006 with corrections to the Cover Date.     

Recovery of low temperature electron irradiation-induced damage in n-type gaas

Undoped n-type GaAa was irradiated near 5 and 77 °K with electrons having incident energies between 0.46 and 1.30 MeV. The recovery of the electrical resistivity and the Hall coefficient upon annealing from 4 to 520 °K was monitored. Changes which occurred upon annealing below 200 °K could be reversed by ionizing radiation. A small amount of irreversible ionization-induced recovery was observed after irradiation near 5 °K. Major irreversible recovery stages were centered near 235 (stage I), 280 (stage II) and 520 °K (stage III). Recovery in stage I and II obeyed first order kinetics. The activation energies of stages I and II were determined as 0.72 and 0.83 eV, respectively. The carrier concentration changes per unit irradiation dose corresponding to the three recovery stages differed in their energy dependence indicating that the defects which are removed in stage III have the lowest threshold energy. The carrier concentration changes per unit irradiation dose corresponding to stages I and III were higher for irradiation near 5 °K than for irradiation near 77 °K.     

Defect study on electron irradiated GaAs by means of positron annihilation

Measurements of the positron lifetime and Doppler-broadened annihilation-radiation have been performed in electron-irradiated GaAs. The positron lifetime at the irradiation induced defects was 0.250 ns at 300 K. The defect clustering stage was found to occur at around 520–620 K, and the coarsening and annealing stage is believed to be above 620 K. Similar annealing stages were also observed in GaAs lightly doped with Si (0.2×10¹⁸ cm^–3). Both the lifetime and the S-parameter in the irradiated GaAs were found to decrease with temperature from 300 K to 100 K, suggesting the coexistence of shallow traps in electron irradiated GaAs.     

肉苁蓉不同生育阶段矿质元素含量

应用ICP -AES技术测定了肉苁蓉不同生育阶段矿质元素含量.结果显示:(1)肉苁蓉药材的最佳采收期(肉质茎生长期),常量矿质元素中K含量高达9.45 mg·g-1,五种常量矿质元素的含量比例为K∶Na∶P∶Ca∶Mg=12∶ 3.4∶1.6∶ 1.4∶1,微量矿质元素中Fe含量最高为97.31 μg· g-1,五种微...     

Evaporation-coupled wetting of ZrO2 by molten Mg in Ar atmosphere

The wetting behaviors of molten Mg drops on polycrystalline ZrO₂ substrate surfaces were studied in a controlled Ar atmosphere at 948–1173 K using an improved sessile drop method. The ZrO₂ substrate is virtually not wetted by molten Mg at temperatures below 1173 K. The wetting and evaporation stages according to different variation behaviors of contact angle, contact diameter and drop height were identified. Six representative modes were proposed to describe the evaporation-coupled wetting behaviors during different stages. The competitions between surface oxidation, chemical reaction and drop evaporation were discussed to account for the mechanisms for various wetting behaviors at different temperatures. The chemical reaction leads to the formation of more wettable MgO phase at the interface; however, it yields only an inconspicuous improvement in the wetting due to enhanced Mg evaporation.     

Thermoelectric power of electron-irradiated graphite at low temperatures

The thermoelectric power (TEP) of very well oriented, nearly single-crystal graphite irradiated at 333 K by 3 MeV electrons was measured along the basal plane direction above 5 K. Changes in the low-temperature dependence of the TEP after different stages of annealing, at 410 and 520 K, have also been investigated. Analysing carefully the experimental data, the phonondrag component S_ph of the TEP is extracted and compared with the theory of Jay-Gerin and Maynard. As a check of the concentration of the irradiation defects, deduced from this analysis, measurements of the thermal conductivity were made on the same samples. The results are found to be in good agreement.     

Low temperature photoconductivity in electron - irradiated p-type Si

The photoconductivity spectra of p-type silicon irradiated at ～15 °K with 1.2 MeV electrons were studied in the wavelength range from 1.2 to 5.5 μ at temperatures from 23 to 80 °K. The 3.9 μ photoconductivity band appears immediately after irradiation in all crystals already at low temperatures, giving further evidence that it is due to the divacancy formed directly during irradiation by electrons. Three main annealing stages of the photoconductivity have been observed; (a) below 160 °K, (b) 160–250 °K, and (c) 280–360 °K. A radiation-induced deep level at E_v , +(0.12±0.02 eV disappears upon annealing at stage b. The annealing behavior of the spectra depends strongly on the measuring temperature. The dependence of the spectra on chopper speed was also investigated.     

The vacancy-interstitial pair in electron irradiated germanium

We have studied the influence of the nature and concentration of donor impurity on the 65°K and 35°K stages in electron irradiated n-type germanium. Because the nature of the impurity does not influence the 65°K stage and because this stage is present alone in lightly doped samples, we confirm that it is associated with the annihilation of a vacancy-interstitial pair. Because the 35°K stage is directly connected to the impurity concentration, and not to the free electron concentration, we conclude that it is associated with the annihilation of a vacancy and interstitial-impurity pair. We have shown that the annihilation of the vacancy-interstitial pair occurs through the interstitial mobility at 65°K, 27°K and 4.5°K depending on its charge state, and that the interstitial-impurity mobility occurs at 35°K.

Our model explains easily the radiation annealing, the behavior of irradiated p-type germanium and can be extended to the case of indium antimonide and perhaps of silicon.     

Pseudoelastic deformation and generation of reactive stresses in a Cu-Al-Ni shape-memory alloy in the temperature range 4.2–293 K

Pseudoelastic deformation and the magnitude of reactive stresses in Cu-14.2% Al-4.5% Ni shape-memory alloy single crystals were studied experimentally in the temperature range 4.2–293 K. It is established that pseudoelasticity and the shape-memory effect are observed in this alloy over the entire temperature range indicated above. It is found that, as the constrained samples are heated at a constant rate from liquid-helium temperature, the reactive stresses increase continuously at temperatures of up to 100 K and then remain constant. When the temperature of preliminary deformation is 77 K, the generation of reactive stresses with an increase in temperature occurs by two stages, which agrees with the multistage behavior of the pseudoelastic-deformation curves of this alloy above the liquid-nitrogen boiling temperature. Using the theory of diffuse martensitic transitions, a quantitative calculation is performed of pseudoelastic-deformation curves and reactive-stress curves over the temperature range 4.2–293 K under conditions of two-stage behavior of the martensitic transformation.     

RHEED intensity oscillations during epitaxial growth of fcc Fe on Cu(001)

Up to 14 strong intensity oscillations of the specular beam in reflection high-energy electron diffraction (RHEED) have been observed during the epitaxial growth of face-centered (fcc) Fe on Cu(001) in the temperature range between 333–370 K. The amplitudes of these oscillations are strong even in the initial stages of growth. This provides evidence that the hetero-epitaxial growth of fcc Fe on Cu(001) proceeds predominantly layer-by-layer-like in that temperature regime. For growth at 300 K, initial Fe-bilayer-island formation followed by predominant layer-by-layer growth above 2 monolayers (ML) of Fe is observed. 3D growth prevails at ˜ 100 K.     

The oxidation of Ni(100) studied by medium energy ion scattering

We have used Rutherford backscattering (RBS) in combination with channeling and blocking to study the initial stages of oxidation of the Ni(100) surface at 325 and 415 K. Not only the oxygen coverage as function of exposure has been measured, but also the amount of nickel taking part in the oxidation process, both quantitatively. RBS results for the oxidation at both temperatures are consistent with the lateral growth of NiO islands.     

High-dose reactor irradiation of iron at 4.6 K: Dose and recovery curves of electrical resistivity

The increase of residual resistivity ?_o of iron during reactor irradiation at 4.6 K has been studied up to a fast neutron dose as high as 1.07 × 10¹⁹ n/cm². The outstanding result is a negative curvature of the differentiated dose curve which probably has to do with the ferromagnetic nature of Fe. Isochronal annealing showed pronounced stages I and II but only little recovery between 300 and 400 K (formerly called stage III).     

Thermally stimulated conductivity induced in SrF2:Tb by u.v. light

Thermally-stimulated-conductivity was excited in SrF₂:Tb crystals by non-ionizing u.v. light. The electrical glow curves were studied in the range 80°–300°K, and thermal activation energies were computed by various methods. A composed glow peak, with maxima at 157° and 169°K, is attributed to the two stages of thermal decay of V_K centers.     

Annealing of γ-ray irradiated lithium compensated p-type silicon

Abstract

Annealing behavior of electrical properties and photoluminescence spectra both at 77 °K in electron-irradiated melt-grown n-GaAs were investigated. Defects electrically active in the Hall mobility and carrier removal anneal through two stages centered at 250° and 460 °K. From the temperature dependence of carrier concentration the existence of a defect level located near 0.15 eV below the conduction band is supposed. Several emission bands are resolved at 1.51, 1.47, 1.415, 1.305 and ～1.2 eV in photoluminescence experiments. Electron irradiation (1.5–2.0 MeV) causes a remarkable decrease in emission intensity of 1.51 and ～1.2 eV bands. Recovery of emission intensity occurs remarkably when samples are annealed to 520 °K which would correspond to the 460 °K annealing stage for carrier concentration and Hall mobility. The 250 °K annealing stage is not observed in photoluminescence experiments. The 1.415 eV peak appears clearly after irradiation and grows remarkably with the 520 °K annealing, especially in Si-doped samples, resulting in large reverse annealing. This band is tentatively speculated to be a complex of Si on As site with As vacancy. Moreover, in samples doped with Te a new emission band at 1.305 eV (9500 Å) is observed after 470°–620 °K annealing.     

Studies of first-stage F-centre production in alkali halides doped with strontium

KBr crystals doped with strontium have been X-irradiated at 293 K. The reduction in single impurity-vacancy dipole concentration has been measured using I.T.C. techniques and is found to be proportional to and in quite close numerical agreement with F-centre growth in both first and second stage F-centre production, this being in agreement with previous results in KCl(Sr). The growth of the absorption band peaking at 263 nm was studied and was found to be proportional to F-centre growth during the earlier stages of colouration, indicating that the responsible centres are a major complement of the F-centres. Ionic conductivity experiments show little agreement between the decay of conductivity and the growth of F-centres during X-irradiation of KCl(Sr) crystals at 293 K.A model is developed in which interstitials are trapped at impurity-vacancy dipoles and in which the two stages of F-centre production is the result of dynamic processes involving modifications of the excitonic mechanism or of back reactions.