Radiation of a relativistic electron in the case of planar channeling in a crystal

The spectral and polarization-angular properties of the radiation of an ultrarelativistic electron are investigated in general form in the case of planar channeling in an anisotropic crystal. It is shown that to describe the characteristics of the radiation it is sufficient to know only the value of the effective field (potential) on the trajectory axis of the channeled electron.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 23–26, March, 1981.     

Quadrupole coupling in EuO due to lattice imperfections

From ¹⁵³Eu nuclear spin-spin relaxation measurements it is concluded that quadrupole effects observed in ferromagnetic EuO are due to lattice imperfections.     

Reinvestigation of crystal growth of thiosemicarbazide potassium chloride and thiosemicarbazide lithium chloride

Reinvestigation of the growth of thiosemicarbazide potassium chloride crystal (1) (Chandrasekaran et al. [1]) and thiosemicarbazide lithium chloride crystal (2) (Maadeswaran et al. [2]), unambiguously confirms that compounds 1 and 2 are pure thiosemicarbazide and do not contain any alkali metal or chloride ions. In this paper we demonstrate the use of classical halide test, flame test, as well as infrared (IR) spectra for correct product characterization.     

Resonance effect in transition electron channeling

We have studied the effect that the discreteness of atomic planes has on electron motion in crystals. The characteristic orientation angles found for a crystal correspond to the maximum probability of transitions in the energy spectrum of associated electron motion.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 58–62, November, 1986.     

Interference effects in two-dimensional electron channeling

Interference effects have been identified with two-dimensional channeling features in current image diffraction (CID) patterns from Al(001) and Al(111) surfaces. These channeling lines are associated with the emergence conditions of {10} type LEED beams for both surfaces. The interference is seen as pairs of narrow, closely-spaced, parallel lines which move spatially with energy changes as calculated from theory. Because the surface potential barrier is a factor at these low energies in the scattering process, dynamic calculations can be expected to provide information about this part of the surface structure.     

Isotopic mass effects for low-energy channeling in a silicon crystal

Monte Carlo (MC) simulations have been used to study the low-energy channeling of ¹⁰B and ¹¹B ions along the [100] axis in Si crystal. MC simulations show that the critical angle Ψ_C ≈ 15.3(keV/E)^1/2 (in degrees) for the channeling of isotopic ¹⁰B ions and Ψ_C=14.5(keV/E)^1/2 (in degrees) for the channeling of isotopic ¹¹B ions, where E is the incident energy. This means that (Ψ_{C for 10B ions}/Ψ_{C for 11B ions})≈ (15.3/14.5)≈ (11/10)^1/2.     

Energy transfer from fast atomic projectiles to a crystal lattice under channeling conditions

Neutral Ne atoms with keV energies are scattered under channeling conditions, i.e., at a glancing angle of incidence, from a LiF(001) surface. By means of a time-of-flight method with a pulsed neutral beam, energy distributions for scattered projectiles are obtained. We find for this specific system that the small energy transferred to the crystal lattice during channeling via binary collisions with large impact parameters dominates the dissipation of projectile energy, whereas all other excitations of the solid can be brought to a negligible level.     

Anomaly of specific heat due to kinks

Finite temperature corrections to classical kink free energies for the sine-Gordon and ø⁴ chains are obtained analytically by means of the transfer integral method. These corrections reveal that kink excitations cause a Schottky-type anomaly of specific heat at low temperatures. The numerical results of Schneider and Stoll are explained qualitatively.     

Advances in electron emission channeling measurements in semiconductors

This paper reports on recent advances in the application of electron emission channeling to studies of the lattice location of radioactive probe atoms in semiconductors. The introduction of position-sensitive electron detection has resulted in an improvement in the experimental efficiency of this method by two orders of magnitude. Electron emission channeling now is able to carry out detailed lattice location studies, and is especially interesting for cases where conventional ion beam lattice location techniques cannot be applied due to a lack of sensitivity. Characteristic features of electron emission channeling with position-sensitive detection are discussed and illustrated by results on the lattice location of Er in Si and GaAs, and on the lattice sites and stability of implanted transition metals in Si. This revised version was published online in July 2006 with corrections to the Cover Date.     

High-efficiency deflection of high-energy protons through axial channeling in a bent crystal

Beam deflection due to axial channeling in a silicon crystal bent along the 111 axis was observed with 400 GeV/c protons at the CERN Super Proton Synchrotron. The condition for doughnut scattering of protons by the atomic strings of the crystal was attained. Such a condition allowed one to observe a beam deflection of 50 murad with about 30% efficiency. The contribution of hyperchanneled states of protons to the observed beam deflection was less than 2% according to simulation results.     

Potential of planar channeling in the surface layer of a LiH crystal

It is shown that the potential in the surface layer of a LiH crystal somewhat differs from the bulk value. The difference is extremely small (about 3%). It is also demonstrated that the thickness of the layer where the potential changes is negligible compared with the dechanneling length.     

Dynamic drag of dislocations in crystal with structural imperfections

A new mechanism of dynamic drag of dislocations is proposed and analyzed. A pair of dislocations is treated as a linear harmonic oscillator. The dissipation mechanism under investigation involves an irreversible conversion of the kinetic energy of moving dislocations into the vibrational energy of the dislocation oscillator. The proposed mechanism is used for calculating the drag force exerted by stationary trapped dislocations on a moving pair of dislocations and the drag of a solitary dislocation by dislocation dipoles. Radiative drag force acting on a moving pair of dislocations is also calculated.     

On transmission profiles in high energy electron channeling

Monte Carlo computer calculations have shown that transmission profiles in high energy electron channeling can be well understood by regarding the direct influence of the string-effect on the electron scattering angle.     

Mn2+doping-induced-effects on commensuration and incommensuration of potassium zinc chloride crystal

Undoped and Mn²⁺-doped with different concentrations of potassium zinc chloride (KZC) crystals were grown from aqueous solutions by slow evaporation. The dielectric constant (ε), dielectric losses (tan?δ) and ac conductivity (σ_ac) of the crystals in the ferroelectric-commensurate, incommensurate and normal phases have been measured as a function of frequency, in the range 1–100?kHz, and temperature, in the range 300–580?K. Virgin samples were subjected to measurements of the frequency dependence at selected temperatures and measurements of the temperature dependence was then followed using the same samples. The increase of ε with T could be due to a combination of conductivity, structural variations and discommensuration (DC) formation and pinning as well. The increase of tan?δ with temperature was attributed to relaxation loss in addition to conduction loss, which increases more rapidly with temperature. The ac conductivity (σ_ac) and tan?δ along the polar axis of KZC increased significantly with increasing Mn²⁺ content while ε decreased. σ_ac changed with frequency according to a power law of the form σ_ac?=?f? ^s where 0.15<s<1.27. A linear decrease of ε and tan?δ with increasing the frequency was also found. The obtained results were treated by considering the effect of Mn²⁺-doping on stripples nucleation, DC evolution/annihilation, DC-lattice formation and DCs pinning by the crystal lattice and/or structural defects for virgin and thermally treated samples.     

“Emergency” channeling radiation due to collisions with point defects

Conditions and causes of a new effect of “emergency” channeling radiation due to collision with point defects have been obtained. Numerical calculations have shown that this effect may be considerable.