Etude des defauts ponctuels dans le zirconium irradie par les neutrons a 24 K

The creation and annealing out of defects in pure zirconium irradiated at 24 K by fast neutrons were followed by measurements of electrical resistivity. We have also determined the influence on these phenomena of metallic impurities and also of an interstitial metalloid solute, by examining two varieties of high-purity metal and some specially prepared zirconium-oxygen alloys (150–600 at. ppm). Using the rise of resistivity due to irradiation as a measure of the rate of damage, we have been able to arrive at an apparent recombination volume of 195 ± 17 atomic volumes, independent of oxygen content. The isochronal recovery spectrum below 345 K incorporates five principal stages, for which interpretations are proposed. Additions of oxygen or of metallic solutes only marginally affect the various annealing stages.     

Plasma cooling by metal snow: II. Discussion of experimental evidence

Experimental results obtained in our laboratory and elsewhere which pertain to the interaction of atomic hydrogen (H⁰ and H⁺) particles with steel and inconel surfaces are discussed in relation to the equations obtained in the preceding article. The agreement as to the effects of temperature of the material, of the roughness factor and of doses is satisfactory. Concerning the results of Tokamak experiments, the effect of surface cracking, accompanied by the liberation of “metal snow” could account for the early appearance of metallic impurities in the centre of the plasma channel; the rapid and localized liberation of high pressure H₂ gas is a likely candidate for the initiation of the unipolar arcs which have been recently detected in several Tokamaks (these arcs themselves can lead to additional impurity release).     

Detection of metallic impurities by resonant ionization spectrometry

A resonant ionization mass spectrometer has been developed for the detection of trace amounts of metallic impurities in solids. This instrument is essentially a quadrupole SIMS in which the sputtered neutrals are resonantly photoionized with a laser beam. The wavelength at which various metals can be ionized by using the simplest 1 + 1 photon scheme as well as the laser power required to saturate the ionization have been determined. The sensitivity of the method has been evaluated with calibrated samples containing known amounts of dopants, and, despite of the simple ionization scheme used, sub-ppma detection limits have been found. Finally the depth profiling capabilities of the instrument have been demonstrated.     

Impurities and oxygen control in lead alloys

The control of the impurities is of major interest for ensuring adequate and safe operation of lead alloys facilities from the viewpoint of the corrosion phenomenon. Specific methods have to be implemented for effective control of the liquid lead-bismuth eutectic quality to the required specifications, as for instance: dissolved oxygen monitoring, dip sampling system, analytical techniques for impurities measurement. Even though the oxygen control in the static facility BIP proved difficult, a better knowledge of kinetics behaviour of the oxygen is acquired. Oxygen sensors gave results in agreement with the theory during the tests achieved on the BIP and on the COLIMESTA facilities. The dip sampler was validated on static device: it allows an effective sampling of the liquid metal melt and an easy separation of the melt from the sampling device when cold. The set of analytical techniques for the measurements of metallic impurities is efficient as well, except for the nickel element, for which the method of analysis with atomic absorption spectroscopy coupled with spiking method should allow the lower detection limit to be decreased below the 5 μg/g as for the iron impurity.     

Multiply charged ions from solids produced under energetic, heavy ion impact

Multiply charged ions from solids under energetic, heavy ion impact have been observed and compared with those from gas atoms and molecules. It is found that the production of multiply charge ions from most metallic solids is significantly reduced, compared to that from gas targets, meanwhile metallic ions from solids of oxided materials seem to be produced in a way similar to that from gas targets. It is also pointed out that impurities adsorbed on surface play an important role in the production of ions from metallic surfaces. Possible applications of energetic, heavy ion bombardment to study of desorption from solid surfaces are discussed.     

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     

Robust determination of effective atomic numbers for electron interactions with TLD-100 and TLD-100H thermoluminescent dosimeters

Lithium fluoride thermoluminescent dosimeters (TLD) are the most commonly implemented for clinical dosimetry. The small physical magnitude of TLDs makes them attractive for applications such as small field measurement, in vivo dosimetry and measurement of out-of-field doses to critical structures. The most broadly used TLD is TLD-100 (LiF:Mg,Ti) and, for applications requiring higher sensitivity to low-doses, TLD-100H (LiF:Mg,Cu,P) is frequently employed. The radiological properties of these TLDs are therefore of significant interest. For the first time, in this study effective atomic numbers for radiative, collisional and total electron interaction processes are calculated for TLD-100 and TLD-100H dosimeters over the energy range 1 keV-100 MeV. This is undertaken using a robust, energy-dependent method of calculation rather than typical power-law approximations. The influence of dopant concentrations and unwanted impurities is also investigated. The two TLDs exhibit similar effective atomic numbers, ranging from approximately 5.77-6.51. Differences arising from the different dopants are most pronounced in low-energy radiative effects. The TLDs have atomic numbers approximately 1.48-2.06 times that of water. The effective atomic number of TLD-100H is consistently higher than that of TLD-100 over a broad energy range, due to the greater influence of the higher-Z dopants on the electron interaction cross sections. Typical variation in dopant concentration does not significantly influence the effective atomic number. The influence on TLD-100H is comparatively more pronounced than that on TLD-100. Contrariwise, unwanted hydroxide impurities influence TLD-100 more than TLD-100H. The effective atomic number is a key parameter that influences the radiological properties and energy response of TLDs. Although many properties of these TLDs have been studied rigorously, as yet there has been no investigation of their effective atomic numbers for electron interactions. The discrepancy between the effective atomic numbers of the TLDs and water is significantly higher than would be indicated by comparing effective atomic numbers calculated via the common - but dubious - power-law method. The mean effective numbers over the full energy range are 6.06, 6.09, 3.34 and 3.37 for TLD-100, TLD-100H, soft tissue and water respectively.     

Effect of the presence of In and Sn in the oxygen chemistry in molten 44.5% lead-55.5% bismuth alloy

The oxygen activity and its control is a key parameter in the use of molten lead-bismuth eutectic LBE in accelerator-driven systems (ADS) reactors. The presence of pollutants in the molten alloy, such as metallic impurities dissolved from the structural material or from other sources, can modify the oxygen chemistry in the molten alloy. For this reason, the oxygen activity in molten LBE has been studied under the presence of In and Sn as a metallic impurities. All the experiments were performed with a shift of the covering gas from a reductive environment (Ar + 10% H₂) to air (20% O₂). These covering gas conditions were used to enable measurement of the electrochemical potential of the sensor in a low oxygen environment and under oxygen saturation conditions of the molten alloy (Me/LBE). All of the tests were performed at 500 °C and in stagnant conditions in an autoclave.     

Reliability analysis of nuclear containment without metallic liners against jet aircraft crash

The present study presents a methodology for detailed reliability analysis of nuclear containment without metallic liners against aircraft crash. For this purpose, a nonlinear limit state function has been derived using violation of tolerable crack width as failure criterion. This criterion has been considered as failure criterion because radioactive radiations may come out if size of crack becomes more than the tolerable crack width. The derived limit state uses the response of containment that has been obtained from a detailed dynamic analysis of nuclear containment under an impact of a large size Boeing jet aircraft. Using this response in conjunction with limit state function, the reliabilities and probabilities of failures are obtained at a number of vulnerable locations employing an efficient first-order reliability method (FORM). These values of reliability and probability of failure at various vulnerable locations are then used for the estimation of conditional and annual reliabilities of nuclear containment as a function of its location from the airport. To study the influence of the various random variables on containment reliability the sensitivity analysis has been performed. Some parametric studies have also been included to obtain the results of field and academic interest.     

Experimental Observation of Hot Spots in a Filippov-Type Plasma Focus Device

In this paper we have presented the experimental results of hot spots observation in different working conditions in Filippov-type Plasma Focus Device “Dena” (90 kJ, 25 kV), analyzing of these results have shown that the working conditions have great influence on hot spots formation. In using the pure gases like D₂, Ar, Kr and Ne the formation of hot spots has been seen rarely, and it can be related to impurities like vapoured metal from the anode surface, also in using the light impurities hot spots were not formed, and only for the heavy impurities like Kr the formation of hot spots have been observed. The discharge voltage also plays an important role in hot spots formation, for voltages less than 16 kV, hot spots have not been observed. Also, using the conic insert anode leads to more and distinct hot spots than the case of flat one. The best results of hot spot observation in these experiments have been achieved by using a conic insert anode and D₂ + 1% Kr as working gas.     

Recording length criteria as applied in ultrasonic testing

An appreciable method used to assess the quality and integrity of safety-related components in light water reactors is the ultrasonic examination, in which case great importance is attributed to the criteria pertaining to recording length and permissible defect size.The development of the recording length criteria as applied when employing this method of examination is portrayed, the latter being based on the criteria which have proven themselves throughout long years of practice in the examination of conventional components. When taking these criteria into account the application of conventional ultrasonic techniques often leads to problems in the case of thick-walled components the reason being that indications are overrated.Taking the design of reactor components as the basic point of consideration, modified criteria are derived particularly when the size of discontinuities calculated by fracture mechanics analyses is taken into account. The introduction of new ultrasonic examination techniques such as, for example, focussed probes revealed that a considerably more realistic assessment is possible and consequently results in a reduction of unnecessary repairs.A comparison of the size of indications determined using conventional and analytical techniques renders possible the anchoring of an intermediate stage in the evaluation of indications which is encompassed in the consideration of the bundle divergence. Thus a new concept is realized for the evaluation of ultrasonic indications detected in reactor components, which in the meantime has found its way into the associated regulatory guides.     

Impurity Measurements in Plasma Boundary of JIPP T-II Tokamak/Stellarator

Impurity transport in the scrape-off layer of the JIPP T-H Tokamak/Stellarator hybrid torus machine in Institute of Plasma Physics, Nagoya University has been investigated by a probe measurement. Silicon and Cu probes were inserted into the boundary plasma during discharges. The surface of the probes was analyzed by several analytical techniques including AES, XPS, RBS and PIXE. Main metallic impurities deposited on the probes were Mo and Fe which originated from the limiters and the inner wall of the vacuum chamber. Depth concentration profile of deposited impurities was measured by AES along with sputter-etching of the surface with Ar ions. Deposited Fe impurity had the maximum concentration at the top surface of the probe, while the depth profile of Mo showed the maximum concentration at around 8 A from the top surface. Transportation energy of these impurities are discussed on the basis of the projected range data.     

Effects of impurity elements on SiC grain boundary stability and corrosion

Grain boundaries(GBs)have critical influences on the stability and properties of various materials.In this study,first-principles calculations were performed to determine the effects of four metallic impurities(Ni,Al,Bi,and Pb)and three nonmetallic impurities(H,O,and N)on the GBs of silicon carbide(SiC),using the Σ5(210)GBs as models.The GB energy and segregation energy(SE)were calculated to identify the effects of impurities on the GB stability.Electronic interactions considerably influ-enced the bonding effects of SiC.The formation of weak bonds resulted in the corrosion and embrittlement of GBs.The co-segregation of Bi,Pb,and O was also investigated in detail.     

Transient annealing of Sn implanted GaAs

High temperature ( 900°C) transient annealing of Sn⁺ implants into GaAs have been studied by secondary ion mass spectroscopy, electrical measurements and transmission electron microscopy. A two-layer encapsulant (Si₃N₄ + AlN) has been used prior to annealing using an incoherent light furnace. Secondary ion mass spectroscopy measurements show that outdiffusion of tin has occurred which depends both on the dose and annealing conditions. The as implanted atomic profiles are wider than the theoretical profiles and up to 17% further broadening occurs during annealing. Electron concentrations approaching 10¹⁹ cm⁻³ have been measured reproducibly. Transmission electron microscopy results show both faulted and unfaulted dislocation loops and dislocation lines, all defects being decorated with precipitates which contain metallic tin. A large concentration of stacking fault tetrahedra is also produced.     

A crossed photon-atom beam method for absolute measurement of total photoionization cross sections on isolated metal atoms: Measurements on Ba and Eu atoms

A crossed photon-atom beam apparatus has been constructed for absolute measurement of total photoionization cross sections of isolated and neutral metallic atoms. The main purpose is to establish the technique which can be used as widely as possible for the metallic elements. Using this apparatus, measurements on Ba and Eu atoms have been made at selected energies in their 4d giant resonance regions 110-140 eV and 140-180 eV, respectively. A monochromatized synchrotron radiation was used as a light source. The target-atom density in the interaction section was determined with accuracy of 9% using the accumulation rate of metallic atoms on a quartz crystal sensor and the average velocity of the atoms obtained by a time-of-flight method combined with a pulsed electron gun. The number of photons was determined with use of a double-ion chamber preferably. The entire systematic errors have been estimated to be 20% for Ba and 27% for Eu. The comparison of the measured cross-section values with previous experimental and theoretical results is reasonable, indicating that the crossed photon-atom beam method is fairly promising technique.     

Calcul du profil d'endommagement par une source isotrope de fragments de fission: Application aux gaines d'acier inoxydable du combustible UO2

The damage distribution produced by an isotropie fission fragments source in contact with a metallic target has been investigated. More precisely, the density of energy transferred by such a source to the target lattice has been computed as a function of the depth in the target. The basis of these calculations is Lindhard's theory which gives for each fission fragment emitted by the source the energy lost in atomic collisions. The results can be applied to the fission fragments damage produced by the fuel of a nuclear reactor in the clad which contains it.     

Low energy nuclear reaction polyplasmon postulate

An explanation is proposed for the nuclear reactions that occur in the electrolysis class of LENR processes. The proposed explanation postulates that a proton, or deuteron, dissolved in the hydrogen bearing metal cathode, absorbs its associated atomic electron to become a short lived state of the neutron with the resulting neutrino in a singular wave function centered on the neutron. The energy required to initiate this endothermic reaction is supplied either by the ion current during electrolysis type experiments, or by ion bombardment in plasma type experiments. It is the energy of this bombardment of the cathode with heavy ions that creates a coherent polyplasmon field within crystalline metallic grains that are present in the metal cathode of typical active electrolysis cells. The LENR process consists of a second order reaction mediated by a coherent plasmon field excited in the conduction electrons in a hydrogen bearing metal that is in the form of crystalline grains of the order of a few microns in dimension. The coherent plasmon field in each grain is called a polyplasmon. The metallic grains typically form during solidification of a metal, the impurities being forced to the grain surfaces. The resulting grain thus forms a resonant structure that can be filled with a number of coherent plasmons, i.e., a polyplasmon.     

含杂质的卢瑟福散射的蒙特卡罗模拟

采用蒙特卡罗方法数值研究了杂质对α粒子卢瑟福散射的影响。杂质原子根据靶材的纯度以给定的概率随机替换靶材原晶格的原子。研究结果表明,考虑杂质后,出射粒子随散射角分布的曲线中形成了新的峰,峰的位置随杂质元素原子序数的增加向大角度方向移动;杂质的原子序数越低、含量越高,对卢瑟福散射出射粒子角分布的影响越明显;同时,入射粒子能量越低,杂质产生的峰对分布曲线的影响越明显。此外,对典型的C6+、N7+等重离子束的卢瑟福散射的模拟计算结果表明,重离子束对杂质有更好的分辨率。     

Radiative Cooling Rates for Low-Z Impurities in Non-coronal Equilibrium State

The local or transient radiation losses in tokamak plasmas can greatly exceed those in the coronal equilibrium. This excess is especially pronounced at the plasma edge. The reason for the increase of radiation in a peripheral plasma is as follows. The impurities are lost fast from the plasma edge and the new impurity source is supplied to this region. The charged states of impurities, therefore, do not reach their coronal equilibrium ones. These impurity ions have more electrons than those in the coronal equilibrium, and as a result emit the higher radiation power. In the simplest case, the non-coronal radiative rate can be determined only by two parameters: the electron temperature \(T_{\text {e}}\) and the so-called “residence parameter” \(n_{\text {e}}\tau _{\text {i}}\), where \(\tau _{\text {i}}\) is the impurity residence time in the plasma. Despite the strong simplification, such an approach allows to do simple estimates of non-coronal radiation. In this paper, two dimensional polynomial fits describing radiative cooling rates and mean charge are obtained for eight impurity species: helium, lithium, beryllium, carbon, nitrogen, oxygen, neon, and argon. The results are presented in figures and tables. The figures show curves calculated from the original atomic database and least-squares polynomial fits to these curves. The tables contains coefficients for this fits. The obtained fits can be useful for qualitative estimates and simple numerical calculations.     

Surface impurities and “clean-up” techniques in ORMAK

The detrimental role played by impurities in thermonuclear devices is now well-known. Experimental studies to identify those impurities residing on the liner, or first wall, of the Oak Ridge Tokamak (ORMAK) have been carried out in the laboratory using Auger Electron (AES) and X-ray Photoelectron (XPS) spectroscopic techniques. Additionally, liner measurements have been made in situ using a small Soft X-ray Appearance Potential Spectrometer (SXAPS). Oxygen, iron and carbon were found to be the major surface impurities and, as confirmed by plasma diagnostics, also the major plasma impurities. Glow discharge cleaning of gold and stainless steel surfaces has been studied using various gases and gas mixtures. Oxygen discharges are very effective and hydrogen moderately effective in removing carbon and hydrocarbon deposits from both types of surfaces. Other parameters involved in the contamination-decontamination process, such as pressure and temperature, have been studied using techniques to controllably contaminate surfaces with hydrocarbons.