Elementary Defects Research Articles

The resistivity recovery of high purity and carbon doped iron following low temperature electron irradiation

Abstract High purity iron (residual resistance ratio ∼5000) and similar iron doped with carbon (15 at. ppm and 67 at.ppm) have been irradiated with 3 MeV electrons at low temperatures. The resistivity recovery of these specimens has been investigated in some detail. The results allow the following interpretations: Two recovery stages, Stage I E (120–140 K) and Stage III (220–278 K), are related to free migration of elementary atomic defects. Other, secondary recovery stages related to long-range defect migration, appeared at 164–185 K, and at 340–360 K, the latter is due to the motion of interstitial carbon atoms. The Stage I E defect and the Stage III defect, both react with carbon. The binding enthalpy for the I E defect-carbon complex is 0.11 eV, for the Stage III defect-carbon ∼1.1 eV. The specific defect resistivity of the Stage II defect-carbon complex is distinctly lower than that of the Stage I E defect-carbon complex. We ascribe the Stage I E defect as an interstitial atom and the Stage III defec...

The efficiency of displacement cascades for the generation and absorption of self-interstitials and vacancies, in a neutron irradiated AgZn alloy

Abstract Strain relaxation measurements were performed during irradiation with reactor neutrons to monitor the enhancement of the stress-induced directional ordering rate associated with the supersaturated point defect population, in a Ag-24 at. % Zn alloy. The corresponding rate evolution was followed from the first seconds after the initiation of flux until long irradiation periods, directly at temperatures where both self-interstitials and vacancies are mobile. The generation of freely migrating elementary defects by the displacement cascades was found to be characterized by a mean cross-section of 160 barns, if referred to fast neutrons (E>1 MeV) in the reactor spectrum, with a bias of a few per cent. From comparison with the estimated total defect production, it was deduced that only 10% of the initially created point defects undergo random diffusion. The production rate of extra sinks for these defects by cascade collapse was determined also, for irradiation temperatures between 0.3 and 0.4 melting temperature. In fact the measured cross-sections were strongly temperature dependent, as the net result of simultaneous sink formation and anneal during high temperature irradiation.

Generalized reptation model

The reptation model is generalized on the basis of a theory which accounts for hindered defect diffusion along the chain. A basic ingredient of the theory is a waiting time distribution for the hops of elementary defects which store length. Important rheological quantities are found to generally depend on fractional powers of the molecular mass rather than on integer powers as in the conventional reptation picture.

An investigation of the mobility of vacancies and interstitials in a Ag,-9 at. % Zn alloy by means of high-voltage electron microscopy

Abstract The characteristics of vacancy and self-interstitial clustering behaviour have been studied in a Ag-9 at. ′% Zn alloy during irradiation in an electron microscope operated at 800 or 1000 keV in the temperature range between 250 and 410 K. The salient feature of the observations was that, for irradiation temperatures below 300 K, only stacking-fault tetrahedra were nucleated while, for irradiations above 360 K, all defect agglomerates were faulted dislocation loops of interstitial type. Deeper insight into the mobility of point defects was gained by the realization of two-step irradiations. These have shown that preformed interstitial loops shrank during subsequent re-irradiation below 300 K. This demonstrates, using conventional methods of analysis for the dynamics of the defect populations associated with a fast particle flux, that vacancies migrate faster than selfinterstitials at low temperatures. The present evidence for this unique behaviour of elementary defects in a metal lattice is in agreement with previous anelasticity results obtained in other concentrated AgZn alloys, in which the single vacancy has been identified to be the faster moving defect.

Defect structures of ion-implanted ?-tin

Single crystalline and polycrystalline α-tin has been implanted at room temperature with 80-keV ions of radioactive119mSn,119Sb, and119mTe. The radioactive nuclei decay to the Mossbauer level of119Sn. Mossbauer spectra of the emitted 24-keV γ radiation have been measured for different source temperatures by resonance counting techniques. Five individual lines in the spectra are characterized mainly by their isomer shifts and Debye temperatures. From these parameters the radiogenic119Sn atoms are concluded to be located in regular substitutional and interstitial lattice sites and in defect complexes. Simple models for the defects are proposed: A Sn-vacancy pair consists of Sn atoms on (nearly) substitutional sites with a dangling bond into an adjacent vacancy. In a complex oxygen-containing defect the Sn atoms have approximately a 5s2 configuration withp-bonds to two nearest neighbour atoms. Sn atoms, having an atomic 5s2 5p2 configuration and large vibrational amplitudes, are concluded to be in non-bonding regular interstitial sites. For special implantation conditions minor fractions of SnO2 molecules are formed in the bulk. The interstitial119Sn and the119Sn-vacancy pairs are proposed to represent elementary point defects in α-tin. Conclusions are also drawn concerning the lattice location and the defects created in the implantation process of the implanted parent isotopes.

Identification and dynamic characteristics of the defects responsible for the radiation enhancement of atomic mobility in concentratedα-AgZn alloys

Strain-relaxation measurements were conducted in order to follow directly under flux the enhanced rate of the stress-induced ordering which occurs in a Ag-30-at.%-Zn alloy, as a result of electron irradiation. From the consideration of activation energies for the quasistationary and stationary states, the migration energies for the two types of elementary defects involved in the observed enhancements were measured to be 0.56\ifmmode\pm\else\textpm\fi{}0.02 and 0.94\ifmmode\pm\else\textpm\fi{}0.02 eV, respectively, for the faster- and the slower-moving species. Further, direct comparison, for specimens in the well-annealed or prequenched condition, of the buildup profiles until a stationary regime is reached, together with quench studies, enabled the unambiguous identification of the faster-moving defect in the irradiated alloy as the single vacancy.

Principles of a classification of defects in ordered media

A classification of defects in ordered media is presented. Based on purely topological concepts, it provides a distinction between elementary (topologically stable) and compound defects. This systematic classification recovers some previous empirically derived results and allows new predictions. It exhibits a striking connection between the nature of defects in an ordered phase and the critical phenomena at the phase transition.

Neuropsychological studies in the USSR. A review (part II).

Human neuropsychology is a new branch of psychological science that was developed at the borders of psychology and neurology. Its goal is to study the brain organization of mental processes and, especially, the higher forms of behavioral processes (1-9). The central problem of this branch of science is the of functions in the brain cortex. Studies in this problem started several decades ago, but its scientific solution is still in the future. Neuropsychology developed as a result of two basic issues: the progress of neurosurgery and a need of psychological science for a reliable knowledge of the cerebral mechanisms of the psychological processes. In the last few decades neurosurgery has made tremendous progress. About 40 years ago, the mortality after brain operations was very high-sometimes 60-70%; now, as a result of new techniques of surgery, treatment of brain edema, and new methods of resuscitation, the mortality does not exceed 8-10%. This means that precise and early local (or regional) diagnosis of the localization of cerebral lesions (e.g., tumor, hemorrhage, vascular disorder) has become a problem of utmost importance. The solution of this problem has certain limitations. Regular neurological methods (analysis of alteration of sensibility and movements, tone and reflexes, limitations of sight and fields of vision, etc.) can be used for a local diagnosis of only a limited part of the cerebral cortex (sensorimotor areas and their pathways). X-ray studies do not bring any precise results, and even the use of contrast methods for arteriography and electroencephalography have certain limits. The restricted limits of regular neurological symptoms is a result of some very important facts: lesions of the highest (secondary or tertiary) zones of the cortex-which are considered as specifically humnan parts of hemispheres-do not result, as a rule, in any elementary sensory or motor defects and remain inaccessible for classical neurological examination. They are associated with alterations of very complex behavioral processes (cognitive processes, elaboration of complex programs of behavior and their control), and that is why one has to establish new complex methods that could be used to study functional disorders evoked by their injuries. It is thus necessary to apply methods of neuropsychology for local diagnosis of lesions of these complex cortical zones.

Neuropsychological studies in the USSR. A review. I.

Human neuropsychology is a new branch of psychological science that was developed at the borders of psychology and neurology. Its goal is to study the brain organization of mental processes and, especially, the higher forms of behavioral processes (1-9). The central problem of this branch of science is the "localization of functions in the brain cortex." Studies in this problem started several decades ago, but its scientific solution is still in the future. Neuropsychology developed as a result of two basic issues: the progress of neurosurgery and a need of psychological science for a reliable knowledge of the cerebral mechanisms of the psychological processes. In the last few decades neurosurgery has made tremendous progress. About 40 years ago, the mortality after brain operations was very high-sometimes 60-70%; now, as a result of new techniques of surgery, treatment of brain edema, and new methods of resuscitation, the mortality does not exceed 8-10%. This means that precise and early local (or regional) diagnosis of the localization of cerebral lesions (e.g., tumor, hemorrhage, vascular disorder) has become a problem of utmost importance. The solution of this problem has certain limitations. Regular neurological methods (analysis of alteration of sensibility and movements, tone and reflexes, limitations of sight and fields of vision, etc.) can be used for a local diagnosis of only a limited part of the cerebral cortex (sensorimotor areas and their pathways). X-ray studies do not bring any precise results, and even the use of contrast methods for arteriography and electroencephalography have certain limits. The restricted limits of regular neurological symptoms is a result of some very important facts: lesions of the highest (secondary or tertiary) zones of the cortex-which are considered as specifically humnan parts of hemispheres-do not result, as a rule, in any elementary sensory or motor defects and remain inaccessible for classical neurological examination. They are associated with alterations of very complex behavioral processes (cognitive processes, elaboration of complex programs of behavior and their control), and that is why one has to establish new complex methods that could be used to study functional disorders evoked by their injuries. It is thus necessary to apply methods of neuropsychology for local diagnosis of lesions of these complex cortical zones.

The influence of neutron radiation on the yield stress and on some activation parameters of polycristalline vanadium

On neutron irradiated polycrystalline vanadium a thermal activation analysis was performed using the stress relaxation method. Irradiation influences both the thermal and the athermal stress component. The radiation hardening at low and intermediate doses can be described according to the dispersed barrier model by a (φ t) 1 2 -dependence. For high doses saturation phenomena are observed. The rate determining process is not influenced qualitatively by irradiation at doses up to 1 × 10 18 n/cm 2. The strength of the rate determining obstacles is reduced at low doses, perhaps as a result of the formation of oxygen-radiation defect complexes. Whereas interstitial oxygen atoms, elementary radiation defects, and complexes composed from both suffer a contribution to the thermal stress component, visible defect clusters in this case probably affect only the athermal stress component. As one can imagine, these findings are dependent on the content of relevant interstitial impurities. In this case the dominating role being played by the oxygen atoms.

Quantum Fact and Fiction III

Part III of this series [A. Landé, Amer. J. Phys. 33, 123 (1965), and 34, 160 (1966), quoted as Parts I and II] continues the critique of the customary interpretation of quantum mechanics. It is directed against the idea that electrons, in opposition to the Born statistical particle interpretation of the wave function, are “wavicles.” Serious conceptual and elementary mathematical defects in Bohr's famous “Discussion with Einstein” are pointed out. The doctrine that position q and momentum p of a particle are blurred over an uncertainty range because both allegedly cannot be measured simultaneously, that q and p do not exist simultaneously, is due to a confusion of analogy with identity of qualities. In its second part, the paper offers a nonquantal derivation of the probability interference law as a necessity under the postulate that the general interdependence between probabilities is to become the ordinary probability addition law in the average. The wave picture of matter violates the postulate of relativity.

Dislocations in the flux line lattice

It is shown that the hexagonal lattice of flux lines probably contains dislocations as elementary lattice defects. The properties of these “flux line dislocations” are discussed, and a mechanism of multiplication is given.

Hardening of Potassium Chloride by Color Centers

The flow stress of KCl crystals containing color centers was studied in a systematic way to determine which color centers produced significant hardening. The color centers were introduced both by additive coloring and by gamma irradiation. Annealing and optical bleaching techniques were used to alter the relative concentrations of defects. For a given concentration of electron excess centers (F, M, R, N, etc.), the irradiated crystals were about ten times harder than the additively colored ones. Possible models for the halogen defect responsible for this high hardness were considered and it was concluded that it must be an interstitial ion or atom. Annealing of additively colored crystals indicated that the ``colloid band was actually two overlapping bands centered at about 735 and 760 mμ. Prior to formation of these bands the crystals became about 40% harder than in the as-colored state indicating the presence of a coherent cluster of elementary defects. The flow stress decreased sharply upon appearance of the colloid bands. A similarly located though broader band was formed after prolonged optical bleaching.

Review of internal friction due to point defects

Simple considerations lead to the expectation that point defects will cause internal friction (by a stress-induced ordering mechanism) in all cases where the introduction of the defects sets up local asymmetric distortions of the surrounding lattice. Three categories of specific examples are considered, in which the relaxation centers are believed to contain 1. (a) a single isolated elementary point defect, 2. (b) two interacting elementary point defects, 3. (c) several interacting elementary point defects. The elementary point defects considered are 1. (1) an interstitial solute atom, 2. (2) a substitutional solute atom, 3. (3) a vacancy, 4. (4) a split self-interstitial. The material for this review is taken from the existing literature with the exception of a brief account of some recent experiments by the author on cold-worked nickel, which relate to the report of a peak due to split interstitials in this metal by Seeger et et al. (17). Due to a background recovery phenomenon, it was not found possible to obtain support for the existence of the peak.

Some physical consequences of elementary defects in diamonds

Using the concept of the defect bond, which is somewhat analogous to the covalent bond, a qualitative theory of the physical properties of pure diamond is developed. The theory allows an explanation of many of the diverse physical properties of different diamond specimens and it leads to a correlation table which is based on a new classification of diamonds according to the presence and the arrangement of vacancies or interstitial atoms. Interpretation of the behaviour of diamond counters is now possible and a beginning is made on the quantitative comparison of theory and experiment, from considerations of the optical absorption properties of diamond in terms of a rudimentary electron energy level diagram.