Parametric x-ray radiation from 500-MeV electrons in a tungsten single crystal with a surface mosaicity less than 1.5′

The yield of parametric x-ray radiation from a tungsten single crystal irradiated with a E=500 MeV electron beam from the Tomsk Sirius synchrotron was studied experimentally in Bragg geometry. The tungsten sample was 1.7 mm thick and had a surface mosaicity less than 1.5′; it was oriented in such a way that the (111) face was at the Bragg angle of θ _B=45° with respect to the electron-beam direction. The x-ray photons were detected at the angle of 2θ _B=90° with respect to the electron beam. The angular distributions of parametric x rays are compared with those calculatedwith allowance for actual experimental conditions.     

Spectrum broadening effect in coherent x-ray radiation of a relativistic electron crossing a single-crystal plate

Based on the dynamic diffraction theory [1], coherent x-ray radiation of a relativistic electron crossing a single-crystal plate at a constant velocity is considered in the Bragg geometry. In the general case of asymmetric reflection of the radiation from the target, expressions are derived for the spectral-angular distribution of parametric x-ray radiation (PXR) and diffraction transition radiation (DTR). For a fixed angle between the electron trajectory and the system of parallel atomic planes of the crystal (Bragg’s angle) it is shown that a decrease in the angle of electron incidence on the crystal plate gives rise to a significant increase in the PXR and DTR spectra, and the causes for spectral broadening for each of these radiation mechanisms are different. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 74–83, March, 2009.     

Grazing incidence diffraction of X-rays in semiconductor heterostructures: Application of the integral mode

The grazing incidence diffraction (GID) of X-rays enables to characterize thin subsurface layers in semiconductor heterostructures having a thickness smaller than 100 nm. The dynamical theory of X-ray diffraction is extended for the case of identical in plane lattice parameters at the heterointerface. Especially the variation in the specular diffracted (220) Bragg intensity measured with open detector (integral mode) is evaluated in dependence on the grazing angle Φ₀ of the primary beam with respect to the (001) surface. Using a parallel beam an oscillation behaviour occurs at the high angle side Θ _c < Φ₀≦0.5⁰(Θ _c is the angle of total external reflection) of the diffraction curveI(Φ₀) which can be related to the thickness of the perfect crystalline part of the epilayert _K . Having an incident beam divergence and a small difference in the effective refractive indices of the layer and the substrate the oscillations are almost leveled. They are further visible in case of a minute inclination of the (220) lattice plane with respect to the surface normal. In the interval 0 < Φ₀<Θ _c the slope of the integral curve depends on the thickness of the subsurface layert _A which does not contribute to the Bragg diffraction. The integral mode is sensitive for layers of about 0<t _A <15 nm and 15<t _K <80 nm. The proposed theory working principally for multilayer structures is presently suplicated to interpret GID curves ofA ^III B ^v heterostructures.     

Zur Tiefenverteilung der durch Elektronenstoß angeregten charakteristischen Röntgenstrahlung von Bor,Kohlenstoff, Aluminium und Silber

The peak intensity of the X-ray emission bands of boron (BK; 67 Å), carbon (CK; 44 Å), aluminium (AlL _2,3; 171 Å), and silver (AgMζ; 40 Å) excited by electron bombardment of evaporated targets has been measured as a function of the thickness of the target and at several accelerating voltages in the range 1 to 4 kV. The electron beam was inclined at an angle of 50° to the surface of the target; the take-off angle for the radiation was about 20°. From these measurements one obtaines the thickness of layers effective in producing X-rays. The influence of surface contamination and oxide layers on the intensity distribution of emission bands is discussed. It is then shown that the effect of anode self-absorption can be evaluated, if the absorption coefficientμ(λ) is available. As an example theL ₃/L ₂ intensity ratio of aluminium, and an averaged depth of X-ray production are calculated; moreover data for the electron range are given and compared with earlier results. Finally the BK-emission band of evaporated boron is presented.     

La/B4C small period multilayer interferential mirror for the analysis of boron

An La/B₄C multilayer interferential mirror with small period d (4.8 nm) was produced by diode sputtering for the detection of the boron K emission by wavelength‐dispersive x‐ray spectrometry at a large Bragg angle (close to 45°). The structure of the mirror was characterized by grazing incidence x‐ray reflectometry and its performance at the energy of the boron K emission (183 eV) was evaluated by means of polarized synchrotron radiation. Spectrometric measurements showed that the La/B₄C mirror improved the detection limit of boron using by a factor of 2 with respect to similar Mo/B₄C mirrors and by a factor of 4 with respect to a lead stearate crystal. Copyright © 2005 John Wiley & Sons, Ltd.     

Observation of spectral line splitting for parametric X-rays

The spectral distribution and energy dependence of the yield of parametric X-rays for 200 to 900 MeV electrons transmitted through a silicon crystal have been measured. The measurements were performed in the Bragg geometry at an angle θ = 19° to the electron beam direction. The effect of spectral line splitting for parametric X-rays was observed.     

Titanium K-edge absorption structure in Ti1−x NbxO2

The fine structure in the titanium x-ray K-edge absorption has been measured in Ti_1−x Nb_xO₂ mixed dioxides (x=0–0.1) with rutile structure in a laboratory-type spectrometer by total electron quantum-yield measurement. The position of the XANES lines is shown to be in good agreement with classical x-ray absorption spectra obtained in transmission. The structure and main features of the XANES spectra, including the effects of impurities and manyelectron excitations, are discussed. It is suggested that the intensity of the B peak characteristic of the titanium K edge depends on the Nb concentration and correlates with the charge state of titanium ions. Fiz. Tverd. Tela (St. Petersburg) 41, 894–896 (May 1999)     

Effect of the surface integral in the torque equation of the electromagnetic angular momentum on the Faraday rotation

A circularly polarized plane wave of infinite transverse extent (δ = ∞) has no spin angular momentum, while a realistic light does carry it. This paradox originates from the presence (δ = ∞) and absence (δ ≈ 0) of the surface integral in the total angular momentum J. The same holds for the torque equation of dJ/dt, so that δ is also connected with the relative Faraday rotation angle Θ_F/θ_F when a radius (a) of a cylindrical medium with optical activity is only a little larger than that (b) of light beam, where Θ_F is the Faraday rotation angle and θ_F is the intrinsic Faraday rotation angle of a medium. It is shown here that it is possible to estimate δ for a realistic light from the drastic variation in Θ_F/θ_F near b/a = 1.     

Efficiency of an electron-beam-pumped chemical laser with an SF6-H2 working mixture

Results are presented from a study of HF lasers pumped by non-chain chemical reactions initiated by a radially convergent and by a planar electron beam. The main channels of formation of vibrationally excited HF molecules are analyzed. The distribution of the energy density of the radiation in the output beam of a wide-aperture laser is measured. In 30 liters of a mixture of SF₆:H₂=8:1 at a pressure of 1.1 atm an output energy of ∼200 J is obtained at an ∼11% efficiency with respect to the energy deposition. It is shown that the admixture of a buffer gas of neon or argon improves the uniformity of the radiation energy distribution in the output beam of an HF laser pumped by a non-chain chemical reaction and initiated by an electron beam, and it also increases the output energy. Zh. Tekh. Fiz. 69, 76–81 (January 1999)     

Radiation from relativistic electrons in homogeneous condensed matter at large angles (≫γ−1)

The radiation spectra from 900 and 400 MeV electrons in thin Ta, Cu, and Sn foils are measured at an angle of 19° with respect to the direction of motion of the beam. The radiation yield and its dependence on the electron energy agree satisfactorily with the theory of polarization bremsstrahlung. This result represents the first direct observation of polarization bremsstrahlung from ultrarelativistic electrons in homogeneous condensed matter. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 3, 145–149 (10 February 1996)     

Shift of the Bragg position in grazing-incidence diffraction

The intensity distribution in grazing-incidence diffraction along the grazing exit angle, a f, has been generally studied assuming the fulfilment of the Bragg condition, both experimentally and theoretically. We consider deviations of the incidence angle and detector position (θ) from the exact Bragg angle, θ _B, as well as variation of the incidence angle with respect to the surface, α _i, and lattice mismatching of layered structures. The so-called surface peak is caused by refraction and appears at the fixed angular position of the critical angle of the total external reflection, α _c. Beside it an additional peak occurs, that is explained by fulfilling the Bragg condition of the lateral wave vector components of incident and diffracted beams. This corresponds to the intersection of the truncation rod and the Ewald sphere. Therefore its angular position in the diffracted scattering fan depends on both α_i and θ ? θ _B. This additional peak is only visible if α _i is below α _C or θ > θ _B. These considerations have been verified experimentally on an InP layer.     

Parametric X Rays in the Region of Anomalous Dispersion

The influence of anomalous dispersion on the intensity of parametric x rays (PXR) is experimentally investigated in the present work. An experiment conducted with an inner electron beam generated by the Tomsk synchrotron with energy E ₀ = 900 MeV is discussed. A Ge monocrystal 0.17 mm thick oriented so that Bragg's angle _B between the electron momentum direction and the (111) plane is 9°30 is used as a target. The experimental data are compared with the results of calculations in the context of the kinematic PXR theory.     

Polarization of leading Λ hyperons produced by neutrons on target nuclei

The polarization of the leading Λ hyperons produced on carbon and lead target nuclei by 4–10 GeV neutrons in the angle range Θ<8.5° with respect to the beam and with only neutral-particle accompaniment is measured: 〈Π〉=−0.096±0.018 for C and 〈Π〉=− 0.128±0.047 for Pb. The dependence of the polarization on the transverse momentum and the Feynman variable is measured. The normalized invariant cross section as a function of p _⊥ ² is found to be approximated by the function A exp(−Bp _⊥ ² ), where the parameter B is independent of the kind of nucleus (B=8.71±0.09 (GeV/c)⁻² for carbon and B=8.83±0.18 (GeV/c)⁻² for lead). Pis’ma Zh. éksp. Teor. Fiz. 64, No. 4, 237–240 (25 August 1996)     

Structural and Torsional Properties of o-Cresol and o-Cresol-OD as Obtained from Microwave Spectroscopy and ab Initio Calculations

The microwave spectra of o-cresol and of o-cresol-OD were assigned using molecular beam Fourier transform microwave (MB-FTMW) spectrometers in the frequency range of 3-40 GHz. Two conformers of o-cresol were measured where the hydroxy group is syn with respect to the methyl group in one case and anti in the other. The transitions of both conformers were split due to internal rotation of the methyl group. For syn-o-cresol we found the rotational constants A=3249.45242(18) MHz, B=2202.02546(18) MHz, C=1323.66277(16) MHz, and the barrier to internal rotation of the methyl group V₃=7.912(46) kJ mol⁻¹. In the case of anti-o-cresol A=3273.80084(18) MHz, B=2196.26747(18) MHz, C=1325.36424(22) MHz, and V₃=4.4256(14) kJ mol⁻¹ was obtained. Moreover we were able to determine the quartic centrifugal distortion constants, the angle between the internal rotor axes, and the inertial a axes, and, for the deuterated species, additionally the deuterium nuclear quadrupole coupling constants.     

Parametric x-ray radiation along the velocity of relativistic electron in a Bragg scattering geometry

Based on the dynamic scattering theory, forward parametric x-ray radiation (FPXR) of a relativistic electron is investigated in a single crystal plate in a Bragg scattering geometry. Analytical expressions for the spectral-angular distribution of FPXR and transition radiation (TR) including the crystal surface orientation with respect to a system of diffracting atomic planes are derived, which allow one to identify the conditions under which a contribution from FPXR is considerable even in the case of a thick absorbing crystal. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 48–56, June, 2007.     

Degenerate four-wave mixing in photorefractive Bi12GeO20 crystals involving internal reflections

Degenerate four-wave mixing in photorefractive Bi₁₂GeO₂₀ crystals involving internal reflections is studied theoretically and experimentally. Two sets of four-wave mixing exist simultaneously. One set is at the Bragg angle while the other is off the Bragg angle. Theoretical and experimental relations between the wavefront reflectivity and the external incident angle of the reading beam, as well as the reference-to-object beam ratio, are investigated.     

On parametric x-ray radiation

The spectral-angular and angular distributions of parametric x-ray radiation generated in the vicinity of the maximum at small angles to the direction of charged-particle motion are studied under the conditions of Laue and Bragg diffraction geometries. Detector parameters at which the dynamical maxima of parametric x-ray radiation can be observed against the background of transition radiation are indicated. The spectral-angular and angular distributions of parametric x-ray radiation are analyzed for the case of backward geometry. The results of the present theoretical calculations are found to be in good agreement with experimental data.     

Generation of X-ray radiation at the interaction of protons with dielectrics

Properties of the characteristic X-ray radiation excited in quartz under 100-keV proton bombardment have been experimentally investigated. The measured intensity of SiK _α radiation for quartz is higher than that for pure silicon by three orders of magnitude. An afterglow from the target is observed for hundreds of seconds after the ion beam is turned off. This enhanced radiation intensity and the afterglow duration have been measured as a function of the beam current, beam grazing angle, and pressure in the chamber. The measurement data indicate that the enhanced insulator radiation is caused by the accumulation and discharge of a positive charge formed in a dielectric and on its surface under exposure to an ion beam.     

Self-adaptive, narrowband tuning of a pulsed optical parametric oscillator and a continuous-wave diode laser via phase-conjugate photorefractive cavity reflectors: verification by high-resolution spectroscopy

A dynamic self-adaptive Bragg grating formed in a photorefractive crystal is shown to be a convenient way to attain single-longitudinal-mode (SLM) operation and narrowband tuning both in a pulsed, injection-seeded optical parametric oscillator (OPO) and in a continuous-wave (cw) extended-cavity diode laser. The pulsed OPO cavity comprises a Rh:BaTiO₃ photorefractive (PR) crystal, a periodically poled KTiOPO₄ nonlinear-optical crystal, and a dielectrically-coated end mirror. A continuous-wave seed beam at 820–850 nm from a tunable SLM diode laser traverses firstly the Rh:BaTiO₃ crystal and then is retro-reflected by the end mirror; this creates a wavelength-selective Bragg grating reflector in the PR crystal, thereby completing the OPO cavity. The cavity stays automatically resonant with the seed radiation, with no need to actively control its length or to make any other mechanical adjustment. One form of injection seeder comprises a novel extended-cavity diode laser (ECDL) design incorporating a self-pumped photorefractive phase-conjugate reflector and a compact, high-finesse tunable intracavity ring filter. This combination facilitates robust tunable single-frequency operation with narrow optical bandwidth. The performance characteristics of the OPO and the ECDL are evaluated by recording high-resolution atomic and molecular spectra. Notably, fluorescence-detected sub-Doppler two-photon excitation at 822 nm, of the 8S ←6S transition in atomic Cs, provides a crucial linewidth test.     

Flow angle from intermediate mass fragment measurements

Directed sideward flow of light charged particles and intermediate mass fragments was measured in different symmetric reactions at bombarding energies from 90 to 800 A MeV. The flow parameter is found to increase with the charge of the detected fragment up to Z = 3–4 and then turns into saturation for heavier fragments. Guided by simple simulations of an anisotropic expanding thermal source, we show that the value at saturation can provide a good estimate of the flow angle, Θ_flow, in the participant region. It is found that Θ_flow depends strongly on the impact parameter. The excitation function of Θ_folw reveals striking deviations from the ideal hydrodynamical scaling. The data exhibit a steep rise of Θ_flow to a maximum at around 250 – 400 A MeV, followed by a moderate decrease as the bombarding energy increases further.