Theory of planar channeling of negative pions

Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 100–104, January, 1995.     

Emission from relativistic fermions in planar channeling

The radiation power from an electron moving in a focusing electrostatic field is derived for the case of planar channeling, with allowance for the electron spin. It is shown that the radiated power is independent of the initial spin orientation for an oscillator potential in the electrostatic field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 63–66, August, 1984.I am indebted for assistance to professors I. M. Ternov and V. G. Bagrov.     

Effective potential of planar channeling in LiH crystals

The problem of calculating the effective potential of planar channeling along the charged (111) and (111) planes in a finite LiH crystal is considered. The criteria of applicability of expressions obtained for an infinite crystal are derived. The surface layer thickness below which these formulas become invalid is estimated.     

Electron and positron planar channeling radiation from diamond

Channeling-radiation spectra have been obtained from a diamond with ≈ 54.5 MeV electrons and positrons. Theoretical calculations are found to fit the experimental results well for electrons, but significant discrepancies exist between theoretical predictions and the positron data.     

Critical angles and minimum yields for planar channeling

Abstract

Local regions on the surface of a sample of ZnO: Zn phosphor powder were deteriorated by low energy heavy ions to a depth of a few hundred Angstrom units. These regions behave as ‘thin films’ in which a negligible small amount of light is produced when an energetic projectile passes through it. The sample was then scanned across energetic ion beams. The scintillation response diminished when the beam impinged onto a film. The decrease, ΔL, in light intensity is the amount of light produced in a phosphor region whose thickness is equivalent to the film thickness. For ¹H and ⁴He the luminescent efficiency, ΔL/ΔE (the ratio of the light produced to the observed energy loss), is approximately independent of energy indicating that the scintillation response depends primarily on the inelastic projectile-electron collisions rather than the elastic projectile target atom encounters.

At a given velocity, a plot of ΔL versus the atomic number of the projectile exhibits oscillatory structure for which a tentative explanation is suggested.     

Enhanced planar channeling of MeV protons through thin crystals

At certain tilt alignments between a MeV proton beam and a planar channeling direction, a single interface lattice rotation within a crystal can result in a lower rate of dechanneling than at planar alignment in a perfect crystal. Such planar channeling enhancement arises when the beam passes through a layer thickness which is a half-multiple of the oscillation wavelength and then encounters a small interface rotation which is matched to the beam tilt angle. The beam is projected into the center of the phase space ellipse below the interface, resulting in certain trajectories undergoing a reduction in their transverse energy, in a manner analogous to stochastic cooling or atom laser cooling.     

Experimental setup for transmission channeling of MeV ions to study edge dislocations

An experimental facility was built where thin metal (Ta) crystals, with known thickness, could be studied by transmission channeling of MeV ions. The details of obtaining a faint beam (1.5–3.6 MeV) of constant flux (±1%) on the target and normalization of the spectrum of forward scattered particles have been discussed with merits and demerits of various setups used. Preliminary experimental results are reported for measuring dechanneling coefficients from edge dislocations produced by cold work, using H⁺ ions. The H⁺ stopping power for Ta in various planar channels and random direction are estimated and using those, it is shown possible to use the setup for thickness measurements of thin crystal films.     

Bending of high energy beams using axial and planar channeling

A very strong and dramatic bending effect has been found for 12 GeV/c positive particles channeled along crystal axes and planes. For a combination of axial and planar channeling the bending efficiency is 5–10%. The maximum bending angle was 52 mrad obtained over a 20 mm long 〈111〉 Si-crystal. The axial channeling is also able to bend negative particles.     

Elastic properties of dislocations lying in a planar boundary

The formulae for the stress field, self-energy and interaction energy of a dislocation lying in a planar boundary between two anisotropic media are given. The solution is applied to the twinning dislocations, especially in bcc metals. A similar solution is also given for a dislocation lying in the boundary between two different isotropic media.     

Landau levels and electron radiation in planar channeling in monocrystals

The influence of a magnetic field on the motion and radiation of an electron is considered for planar channeling in a monocrystal. It is shown that discrete levels analogous to Landau levels appear in the super-barrier domain of transverse energies instead of a continuous spectrum. The spectral composition and intensity of anomalous and normal waves are computed. The possibilities are discussed of the observation of electron radiation with Landau levels.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 88–93, August, 1989.     

Magnetic moment measurement of baryons with heavy-flavored quarks by planar channeling through a bent crystal

The precession angle of a polarization vector is calculated for a positively charged short-lived baryon channeling between single-crystal planes. When very energetic polarized baryons are produced such that the production plane of the baryon is almost parallel to the crystal plane, it is shown that the interaction of the polarization with inhomogeneous electric fields inside the crystal can be neglected from the equation of motion of the particle. In this case, the equation of motion of the polarization vector becomes the same as when the electric field is homogeneous. It is also shown that when the crystal is bent perpendicular to the planar direction, the precession angle of the polarization vector of short-lived baryons can be expressed ass $\text{Δθ}{}_{\mathrm{<mtext>R</mtext>}}{}^{\mathrm{\tau }}\text{=}\text{1}\text{2}\text{γ}{}^2\text{[(2 ? g + g/γ}{}^2\text{)]ντ/R}$ under the same condition as above, where γ is the Lorentz factor, g the g factor of the magnetic moment, R the bending radius of the crystal and τ the lifetime of the particle. It is also shown that in some cases this precession should be large enough to determine the magnetic moment of short-lived particles, such as the charmed baryon Λ_c⁺.     

Experimental determination of the neutron channeling length in a planar waveguide

In neutron waveguides, the neutron wave is confined inside the guiding layer of the structure and can escape from the layer edge as a microbeam. The channeling within the guiding layer is accompanied by an exponential decay of the neutron wave function density inside the waveguide. Here, we report direct determination of the corresponding decay constant, termed the neutron channeling length. For this, we measured the microbeam intensity as a function of the length of a neutron absorbing layer of variable length placed onto the surface of a waveguide structure. Such planar neutron waveguides transform a conventional neutron beam into an extremely narrow but slightly divergent microbeam, which can be used for the investigation of nanostructures with submicron spatial resolution.     

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.     

Generation of X-ray radiation during planar channeling of relativistic electrons in crystals

A classical model of the emission of radiation by relativistic electrons in a crystal has been developed using the form of the potential maximally close to its actual form. The dynamics of electrons with energies 20–25 MeV performing channeling in crystals is simulated numerically. The generation of electromagnetic radiation that accompanies this motion has been considered. It has been shown that, in the given electron energy range, this radiation corresponds to the X-ray spectral band with characteristic photon energies of up to 40 keV. The radiation yield is estimated. The requirements to the electron beam parameters are formulated based on the results of the simulation. It has been shown that numerical simulation gives results that correlate with the analytic results obtained earlier and with the experimental data.     

Oscillating trajectories in planar channeling studied in a double alignment configuration

The scattering yield of protons measured in a particular configuration of planar double alignment from a thin gold crystal exhibits strong oscillations when the incident energy varies, providing a new method of observation of particle trajectories in planar channeling.     

Channeling and axial to planar channeling transition of protons in magnesium oxide

The channeling of 1.7 MeV protons along 〈100〉 axial direction, (100), (110) and (111) planar directions in magnesium oxide single crystals and axial to planar channeling transitions from 〈100〉 to (100), (110) and (210) have been studied experimentally. The experimental data and preliminary analysis of results are presented.     

On radiation damping in planar channeling in the presence of multiple scattering

The effect of radiative damping of transverse oscillations of positrons in the planar channel of a crystal is considered under realistic conditions when multiple scattering of the positrons on the atomic electrons is taken into account.     

The influence of the planar potential form on the channeling radiation spectrum

Energies for transitions between bound states for planar-channeled electrons are calculated. The continuum planar potential constructed from atomic ones in Molier and Hartree-Fock-Slater approximation are used. It is shown that the H-F-S line energies calculations are in a good agreement with the experimental data for diamond.