Measurement of quadrupole moments of unstable nuclei during channeling and the possibility of revealing the effect of vector polarization of tensor-polarized beams of nuclei

General relations are deduced which describe the spin dynamics of beams of nuclei with the initial tensor and vector polarizations upon planar channeling in bent crystals. Our analysis demonstrates the possibility of revealing the effect of vector polarization, as predicted by Baryshevsky and Sokolsky, which occurs upon the planar channeling of a beam of nuclei with initial tensor polarization. The planar channeling of a beam of nuclei with the initial tensor and vector polarizations may be used to determine the quadrupole moments of unstable nuclei with a small lifetime of up to the order of 10^?7 s. The quadrupole moments of nuclei with a lifetime on the order of 10^?7 s cannot be measured by known techniques, including optical methods.     

Vector polarization effect appearing in tensor polarized beams of nuclei under channeling conditions and during measurements of the quadrupole moments of unstable nuclei

General relations describing the spin dynamics of beams of nuclei with initial tensor and vector polarizations have been derived upon planar channeling in bent crystals. The performed analysis indicates that the vector polarization effect predicted by Baryshevsky and Sokolsky can be detected, occurring upon the planar channeling of a beam of nuclei with initial tensor polarization. The planar channeling of a beam of nuclei with initial tensor and vector polarizations can be used to determine the quadrupole moments of unstable nuclei with small lifetimes, up to 10⁻⁷ s. The quadrupole moments of nuclei with lifetimes of about 10⁻⁷ s cannot be measured via known methods, including optical methods.     

Modification of the theory of diffracted channeling radiation for axial electron and positron channeling

A new type of combinational channeling radiation induced by subbarrier (interband) transitions for the transverse motion of relativistic electrons (positrons) is studied. It is known as diffracted channeling radiation (DCR). The formula describing the DCR angular distribution in the case of axial channeling is obtained by taking into account the band structure of energy levels for the transverse motion of electrons (positrons). It is shown that, in the two-wave approximation of the wave function A(r) of virtual photons, the DCR matrix elements in the dipole approximation for axial and plane channeling coincide formally (with the dimension of the problem taken into account). However, the formulas for DCR angular distributions in the cases of axial and plane channeling differ considerably.     

Energy losses of electrons in oriented crystals

Abstract

Within the framework of the multistring model of axial channeling of electrons the method for calculating the losses to radiation in channeling is proposed. The physical model includes the multiple scattering, the beam and target characteristics. The simulated results are compared with the experimental data.     

Atom location in complex lattices: Pb in α-Al2O3

The channeling technique has been used to locate Pb implanted into α-Al₂O₃ single crystal. The main purpose has been to learn how to obtain information about the location of an impurity in a complex structure. A Pb location is proposed according to data of full angular scans through different axial and planar channeling dips.     

Ion-channeling analysis for epitaxial YBa2Cu3Ox superconducting thin films by laser deposition

Rutherford backscattering/channeling has been applied to study structures of as-deposited epitaxial YBa₂Cu₃O_x thin films prepared on {100}SrTiO₃ by laser deposition. The epitaxial growth has been proved by a planar channeling experiment and transmission electron microscopy. An axial angular yield profile for barium along the c-axis has ideal characters of compensating shoulders and of a flat region at the bottom of the channeling dip. The thermal vibration amplitude, which has been determined from a half-angle of the axial angular yield profile by using Gemmell's channeling model for polyatomic crystals, is compared to those from diffraction experiments.     

Simulation of radiation energy losses by channeled relativistic electrons in a crystal

A computer code is developed to calculate the radiation energy losses (RELs) of electrons during both 〈100〉 axis and (100) plane channeling in a thin Si crystal. A computer simulation of these losses is carried out by taking the initial angular divergence of the beam into account, and the REL dependences on the angle of electron entry into the crystal are obtained for both axial and planar channeling (orientational dependences). The calculations are carried out in connection with experiments on the interaction of 20–255 MeV electrons with crystals conducted at the SAGA Light Source linear accelerator (Tosu, Saga, Japan). The simulation results show the possibility of using the orientational dependence of the RELs of channeled electrons in thin crystals to diagnose the initial angular divergence of the electron beam and to orient crystals.     

Intense beam production with ECR ion sources

Electron cyclotron resonance ion sources are now able to attain a beam current as high as some milliamperes, which until a few years ago was obtained only for pulsed laser ion sources with a much higher emittance and energy spread, by keeping also the possibility to produce high charge states close to electron beam ion sources, at much higher intensity. They usually operate at frequencies up to 18 GHz, but now many sources are able to operate or will be able, at 28 GHz frequency or more, with plasma density of the order of 10¹³ cm^?3, much higher than any other source of the previous generation. The state-of-the-art technique will be described along with the major characteristics of the upcoming sources.     

The nonparaxial propagation of the TEM0l doughnut beam with the orbital angular momentum in the far field

The analytical expression for nonparaxial electric field amplitude of the TEM_0l^? doughnut beam with the orbital angular momentum quantum number l is derived in the far field by means of the angular spectrum representation and the stationary phase method. It is shown that the divergent angle of the far field of TEM_0l^? doughnut beam will be smaller with the decreasing of the orbital angular momentum quantum number l or the increasing of the beam waist width w of the initial beam. And the maximal radial intensity of the beam is decreased with its propagation at different rates for different l and w.     

On the orientation effect of the neutron yield increase in <Emphasis Type="Italic">d</Emphasis>(<Emphasis Type="Italic">d,n</Emphasis>)<Superscript>3</Superscript>Hе reactions at an energy of 7–12 keV in TiD<Subscript>2</Subscript> crystals

The orientation dependence of the d(d, n)³He reaction probability in a TiD₂ crystal at a deuteron energy of 7–12 keV is investigated. The BCM-1.0 code developed for calculating the trajectories of channeled particles within classical mechanics is used to simulate deuteron trajectories at (200)-planar channeling in a 0.15-μm-thick Ti crystal with the angular divergence of the beam taken into account. The enhancement of the reaction probability in the computer experiments is 2.1 in the case of a parallel deuteron beam and near-zero crystal entry angles relative to the (200) planes. In the case of a deuteron beam with its angular divergence equal to 1/5 of the critical channeling angle, the maximum reaction-probability enhancement is 1.5. The results of calculations agree qualitatively with recent experiments performed at Tomsk Polytechnic University.     

A study of small impact parameter ion channeling effects in thin crystals

We have recorded channeling patterns produced by 1–2 MeV protons aligned with ?1 1 1? axes in 55 nm thick silicon crystals which exhibit characteristic angular structure for deflection angles up to and beyond the axial critical angle, ψ _a . Such large angular deflections are produced by ions incident on atomic strings with small impact parameters, resulting in trajectories which pass through several radial rings of atomic strings before exiting the thin crystal. Each ring may focus, steer or scatter the channeled ions in the transverse direction and the resulting characteristic angular structure beyond 0.6ψ _a at different depths can be related to peaks and troughs in the nuclear encounter probability. Such “radial focusing” underlies other axial channeling phenomena in thin crystals including planar channeling of small impact parameter trajectories, peaks around the azimuthal distribution at small tilts and large shoulders in the nuclear encounter probability at tilts beyond ψ _a .     

大气湍流中光束束宽扩展和角扩展的比较研究

以厄米-双曲余弦-高斯（H-ChG）光束为例,对H-ChG光束通过大气湍流传输时的束宽扩展和角扩展做了详细研究.用相对束宽和相对角扩展代替束宽和角扩展来研究湍流对光束影响的灵敏程度.研究表明,折射率结构常数C²_n越小,光束束宽扩展和角扩展越小.有较大阶数m,n,较小参数Ω₀和束腰宽度w₀ H-ChG光束的角扩展受湍流影响较小.当传输距离足够远时,这一结论对H-ChG光束的束宽扩展也成立.当传输距离不长时,对H-ChG光束相对束宽随Ω₀和w₀的变化规律做了分析.用数值计算例做了说明,并对结果的正确性做了物理解释.厄米-高斯,双曲余弦高斯和高斯光束在大气湍流中的扩展可作为H-ChG光束的特例来处理. 关键词： 束宽扩展和角扩展 大气湍流 厄米-双曲余弦-高斯光束     

Studies of relativistic electron scattering at planar alignment in a thin Si crystal

Experiments on 255-MeV electron scattering under (220) planar channeling conditions in a Si crystal were carried out at the linac of the SAGA Light Source. The spatial and angular distributions of electrons penetrating through a 20-μm thick Si crystal at different incident angles with respect to the (220) plane were measured, and features characteristic of the planar alignment were identified. The experimental results were compared with computer simulations, and showed a reasonable agreement. A comparison with doughnut scattering at axial channeling in the same crystal was also performed. It was confirmed that the planar alignment effect is weaker than the axial alignment effect. These studies are important for understanding the basic mechanism of electron scattering and radiation processes in a crystal.     

Motion of the spin of particles and nuclei of arbitrary spin in the electric field of crystals

The possibility of verifying the conclusions of quantum theory on the motion of the spin of particles and nuclei of arbitrary spin in an electric field is analyzed. The theory predicts that the planar channeling of particles and nuclei with higher spins (one or more) through straight crystals is accompanied by the rotation of their spin. For some nuclei, the spin-rotation angle per unit length is about 10^?1 rad/cm. For ultrarelativistic nuclei undergoing planar channeling through bent crystals, the spin-rotation angle per unit length is on the order of 1 rad/cm, which makes it possible to verify the validity of the Bargmann-Michel-Telegdi equation for particles and nuclei of higher spins.     

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.     

Observation of channeling and volume reflection in bent crystals for high-energy negative particles

Deflection due to planar channeling and volume reflection in short bent silicon crystals was observed for the first time for 150 GeV/c negative particles, π⁻ mesons, at one of the secondary beams of the CERN SPS. The deflection efficiency was about 30% for channeling and higher than 80% for volume reflection. Volume reflection occurs, in spite of the attractive character of the forces acting between the particles and the crystal planes, in a wide angular range of the crystal orientations determined by the crystal bend angle.     

Ein hochempfindlicher Gegenfeld-Energieanalysator für Elektronen

A device of high sensitivity for the investigation of as well the angular as the energy distribution of an electron diffraction pattern is described. Consisting of an energy analyzer of the retarding field type in connection with scintillator and photomultiplier the device allowed to measure a minimum current of 10^?17 A. This limit of detectability was only determined by the noise of the initial electron beam and a signal to noise ratio of 5. The energy resolution of the device was only limited by the thermal spread of the beam. By means of a deflection condensor the diffraction pattern was shifted over the diaphragm of the analyzer.     

Diffracted channeling radiation for axial electron channeling

It is shown that, in contrast to diffracted channeling radiation (DCR) in the case of planar channeling, transitions of type 2 → 1, 3 → 2, 4 → 3, and so on make the main contribution to DCR in the case of axial channeling along an isolated axis. The angular DCR distributions for channeling of electrons with the energy corresponding to the Lorentz factor γ = 100 are calculated for an isolated axis using the Coulomb-type potential.