X-ray and magnetic-field-enhanced change in physical characteristics of silicon crystals

The effect of low-energy (W = 8 keV) low-dose ((0.3?C7.3) × 10² Gy) radiation and a dc magnetic field (B = 0.17 T) on structural, micromechanical, and microplastic characteristics of silicon crystals has been studied. The features in the dynamic behavior of dislocations in silicon crystals, which manifest themselves upon only X-ray exposure and combined (X-ray and magnetic) exposure, have been revealed.     

Heavy fermion contributions to the anomalous magnetic dipole and quadrupole moments of theW-boson

The contribution of a massivet-quark to the anomalous magnetic moment (Δκ) and the quadrupole moment (ΔQ) of theW-boson is calculated. An upper bound of Δκ=1.5×10^?2 and ΔQ=2.5×10^?3 for the standard model is obtained. Additional contributions from extraE ₆ fermions is also discussed.     

The solution of the kinetic equation for phonon heat conductivity by the method of momenta and the influence of isotopic disorder on phonon heat conductivity of germanium and silicon crystals at T=300 K

The problem of solving the kinetic equation for the heat conductivities of dielectric substances and semiconductors by the method of momenta is discussed. Microscopic models are used to estimate the effect of isotopic disorder on the thermal resistance of germanium crystals in the multimomentum approximation. The contributions of acoustic and optical phonons are taken into account. Excess thermal resistance ΔW of samples with a natural isotopic composition compared with highly enriched samples is calculated. For germanium, the theoretical and experimental Δ W values are in close agreement with each other. For silicon, the theoretical ΔWvalue is much smaller than its experimental excess thermal resistance.     

Schwinger mechanism of electron-positron pair production by the field of optical and X-ray lasers in vacuum

The probability W of e ⁺ e ^?-pair production in vacuum by an intense time-varying electric field created by optical or X-ray laser is calculated. Two characteristic regions γ?1 and γ?1 of adiabaticity parameter γ are considered. With an increase in γ and on passing from monochromatic radiation to a finite laser pulse, the probability W increases sharply (for the same field intensity). The dependence of the probability W and the electron and positron momentum spectrum on the pulse shape is discussed (the dynamic Schwinger effect).     

Test of QCD indū→W − γg,the radiation amplitude zero and the magnetic moment of theW boson

We have calculated the differential cross-section for the processdū→W ^? γg (Jet). It is found that, although the radiation amplitude zero, which occurs for the lowest-order processdū→W ^?γ, is spoiled, there remains a very large dip. Hence, both processes can be used to measure the magnetic moment of theW boson and the value of the quark charges. The presence of a dip is a test of the gauge theoretical value for the magnetic moment of theW bosong=K+1=2, and the angle at which the dip occurs is a measure of the quark charges.     

The Schwinger effect and possibilities for its observation using optical and X-ray lasers

The probability W of e ⁺ e ^? pair production from a vacuum in an intense variable electric field generated with powerful optical or X-ray lasers is calculated. Two characteristic ranges are considered: γ ? 1 and γ ? 1, where γ is the adiabaticity parameter. The probability W is shown to increase sharply with γ (at a fixed field strength F). The dependence of W and the momentum spectrum of electrons and positrons on the laser pulse shape is discussed in detail. Numerical calculations were performed for a laser pulse with a Gaussian envelope and for some pulsed fields.     

Numerical experiments on low-energy ion scattering at a surface containing adsorbed impurity atoms

The energy distributions of Cs⁺ and W⁺ ions scattered, respectively, at Mo and W single crystals, the surfaces of which contain adsorbed oxygen, nitrogen, and cesium atoms, are calculated via the molecular dynamics method. It is demonstrated that the energy spectra are sensitive to the impurity atoms of a surface. When compared with the energy distributions corresponding to a pure surface, even a partial monolayer of these atoms can modify their shape. A peak in the scattered-ion intensity is commonly shifted to the lowerenergy region if the adsorbate is light and to higher energies if the adsorbate is heavy.     

Electroweak one-loop corrections to the decay of the charged vector boson

The electroweak radiative corrections to the decay widths of theW-boson, Γ \((W \to l\bar v,\bar ud,\bar cs)\) , have been calculated in the standard theory. The results are presented in terms of an electroweak form factorρ ^W and their dependence onm _t , andM _H (masses oft-quark and higgs boson) is studied. Typically,ρ ^W ?1 is of an order of one percent. The differenceρ _lv ^W ?ρ _qq′ ^W is negligible, 0.046%. The calculational scheme used is described in detail.     

Limits to possible scalar-boson mass and coupling from e+e− collisions

Measurements of e⁺e^? → e⁺e^? at 2.8 GeV are reported and interpreted in terms of limits for the mass and coupling of a possible scalar boson of the type introduced in recent renormalizable models of weak interactions. In particular, in the Georgi-Glashow scheme of leptons we find that the scalar boson mass must be larger than 10 GeV for an m_W = 10 GeV (m_W mass of the W-boson) and of 6.5 GeV for m_W = 15 GeV. Alternatively its coupling is extremely weak.     

W-production viaZ-decay

We calculate the decay rate for the processZ Boson→W Boson+fermion+antifermion. The result is applied to compute the decay rates for \(Z \to W^ + + l + \bar v_l \) ,l=e, μ or τ andZ→W ⁺+anything in the Weinberg-Salam model. At the present experimental value of sin² θ _w=0.23 the branching ratios for the above processes are \(\Gamma (Z \to W^ + l\bar v_l )/\Gamma (Z \to all) \simeq 9 \times 10^{ - 9} \) and Γ(Z→W ⁺+anything)/Γ(Z→all)?8×10^?8.     

Growth and comparison of physicochemical properties of pure,Ca and Sr doped NH4Sb3F10 single crystals for electro optic applications

Single crystals of pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ are grown by slow evaporation technique. The effect of dopants on the growth and physicochemical properties also have been investigated and reported for the first time. The grown crystals are characterized with the aid of single crystal X-ray diffractometry to confirm the crystal structure. EDAX studies are done to confirm the presence of dopants in the crystal lattice. The vibrational frequencies of various group ligands in the crystals have been derived from the Fourier transform infrared (FT-IR) spectrum. From the optical absorption spectrum the band gap energy was calculated and it was found to be 5.76, 6.29 and 6.35 eV for pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ crystals respectively. Thermal stability of the sample has been analysed using TG-DTA analysis. The activation energy of pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ crystals were calculated from the dc conductivity measurements and it is found to be 0.2728, 0.2816 and 0.3622 eV Experimental results shows improved physicochemical properties when the dopant is added to the pure material.     

Photoinduced semiconductor-metal phase transition in a peierls system

The dynamical equation for the order parameter of the metal-semiconductor phase transition, as well as the kinetic equation for the density of nonequilibrium electron-hole pairs of a Peierls system in a light field, has been derived. An expression for the time τ of the nonthermal photoinduced semiconductor-metal phase transition has been obtained from these equations for the case of an ultrashort light pulse. It has been shown that, to initiate the phase transition, the energy density W of the light pulse must be higher than the critical value W _c. The W _c, τ, and optical absorption coefficient γ₀ that are calculated in the framework of the proposed model are in agreement with the experimental data (W _c ≈ 12 mJ/cm², τ ≈ 75 fs, and γ₀ ≈ 10⁵ cm^?1) on the irradiation of a vanadium dioxide film by a laser pulse with a duration of τ_p ≈ 15 fs, a photon energy of ?θ₀ = 1.6 eV, and an energy density of W = 50 mJ/cm².     

Determination of relaxation times of ground electronic state vibrational levels of mixed molecular crystals

The stimulated emission spectra of mixed molecular crystals were investigated with the Nd glass lasser third harmonic excitation at 4.2 K. Napthalene crystals doped with β-naphthyl-n-biphenylyl ethylene and dibenzyl doped with naphthacene in various concentrations were studied. Relaxation times of the ground state vibrational levels in mixed molecules were obtained by use of the dependence of stimulated emission intensity upon excitation energy for naphthacene in dibenzyl τ₁ of the vibrational level at 317 cm^-1 was ～ 3 × 10^-9 s; for β-naphthyl-n-biphenylyl ethylene in naphthalene τ₁ of the 1629 cm^-1 vibrational level was ～ 10^-10 s.     

Remarks on the lifetime of charmed baryonΛ c +

The interference andW-exchange contributions toΛ _c ⁺ inclusive nonleptonic decay rate are expressed in terms of matrix elements of effective fourquark operators and evaluated in the MIT bag model. It is found that although theW-exchange is not necessarily subject to helicity and color suppression, it does not suffice to explain the measured lifetime ofΛ _c ⁺. The observed semileptonic branching ratio ofΛ _c ⁺, however, requires that its inclusive decay rate be dominated by the nonspectator contribution and thus theW-exchange be substantially enhanced by some nonperturbative effects. The implication for exclusive two-body decays ofΛ _c ⁺ is briefly discussed.     

Decays of intermediate vector bosons,radiative corrections and QCD jets

We investigate decay properties of the intermediate vector bosons W^± and Z⁰. QED and QCD radiative corrections to leptonic and hadronic decay modes are calculated. Implications of the results for decay widths, branching ratios, determination of the number of neutrino species, e-μ-τ universality and properties of hadronic jets produced in W^± and Z⁰ decays are examined.     

Middle infrared luminescence of Tb in silver halide crystals and fibers

The optical absorption and the luminescence emission were investigated in AgCl_xBr_1−x crystals (0<x<1) doped with Tb³⁺ ions and in fibers extruded from these crystals. Strong luminescence emission in the middle infrared (MIR) in the spectral range 4.2-5.6 μm was observed for the first time in such crystals and fibers.¹ Various optical parameters were calculated for the Tb³⁺-doped crystals, using the Judd-Ofelt approximation. The measured and the calculated results have indicated that these doped crystals could be used for the development of solid-state lasers or fiber lasers operating in the middle infrared.     

Microscopic calculation of the surface absorption in the optical potential

We calculated the contributions of the two-particle one-hole (2p-1h) and the one-particle two-hole (1p-1h) excitations to the imaginary partW(E, R) of then-⁴⁰Ca optical potential. The bound single particle states and energies of the⁴⁰Ca nucleus are calculated quantum mechanically by solving the Schrödinger equation with a Woods-Saxon potential. For the excited states in the continuum we use the Thomas-Fermi approximation. Different forms of contact residual interactions have been tested. A combination of aδ-force and a smeared SDI can fit the phenomenologicalW(E, R).     

Optical spectra and emission characteristics of terbium-doped potassium–lead double chloride crystals (KPb<Subscript>2</Subscript>Cl<Subscript>5</Subscript>:Tb<Superscript>3+</Superscript>)

Optical transitions in KPb₂Cl₅:Tb³⁺ crystals are studied experimentally and theoretically. The absorption cross-section spectra are plotted and the oscillator strengths of transitions from the ground terbium state to excited multiplets are determined. Intensity parameters Ω_t for KPC:Tb³⁺ are determined by the Judd–Ofelt method to be Ω₂ = 2.70 × 10^–20 cm², Ω₄ = 7.0 × 10^–20 cm², and Ω₆ = 0.72 × 10^–20 cm². These values were used to calculate such characteristics of spontaneous radiative transitions as oscillator strengths, probabilities of radiative transitions, and radiative lifetimes. The emission spectra of KPb₂Cl₅:Tb³⁺ crystals upon UV excitation and the decay kinetics of luminescence from the excited ⁵ D ₃ and ⁵ D ₄ levels are studied experimentally, the lifetimes of these levels are determined, and the dependences of the rates of nonradiative relaxation from the excited ⁷ F _j (j = 0–5), ⁵ D ₄, and ⁵ D ₃ levels to lower-lying terbium levels are calculated. It is shown that the population of the ⁵ D ₄ level in KPC:Tb³⁺ crystals occurs according to a cascade scheme, which leads to quenching of the ⁵ D ₃ level. The calculated data agree well with the known experimental rates of multiphonon nonradiative transitions for Dy:KPC, Nd:KPC, Er:KPC, Tb:KPB, and Nd:KPB crystals. It is shown that transitions in the near-IR (3–6 μm) region in double halide crystals (MPb₂Hal₅) are almost unquenched and the rates of nonradiative relaxation of excited levels spaced by energy gaps ΔE _ji > 1000 cm^–1 are W _ji ^NR < 10³s^–1. This circumstance suggests that it is possible to obtain stimulated emission in KPb₂Cl₅:RE³⁺ crystals in the IR spectral region up to 6 μm.     

Structure and dielectric behavior of TlSbS2

A comparison of structure and dielectric properties of TlSbS₂ thin films, deposited in different thicknesses (400–4100 Å) by thermal evaporation of TlSbS₂ crystals that were grown by the Stockbarger–Bridgman technique and the bulk material properties of TlSbS₂ are presented. Dielectric constant ε ₁ and dielectric loss ε ₂ have been calculated by measuring capacitance and dielectric loss factor in the frequency range 20 Hz–10 KHz and in the temperature range 273–433 K. It is observed that at 1 kHz frequency and 293 K temperature the dielectric constant of TlSbS₂ thin films is ε ₁=1.8–6 and the dielectric loss of TlSbS₂ thin films is ε ₂=0.5–3 depending on film thickness. In the given intervals, both of dielectric constant and dielectric loss decrease with frequency, but increase with temperature. The maximum barrier height W _m is calculated from the dielectric measurements. The values of W _m for TlSbS₂ films and bulk are obtained as 0.56 eV and 0.62 eV at room temperature, respectively. The obtained values agree with those proposed by the theory of hopping over the potential barrier. The temperature variation of ac conductivity can be reasonably interpreted in terms of the correlated barrier hopping model since it obeys the ω ^s law with a temperature dependent s (s<1) and going down as the temperature is increased. The temperature coefficient of capacitance (TCC) and permittivity (TCP) are evaluated for both thin films and bulk material of TlSbS₂.     

Analysis of transverse momentum and event shape invN scattering

The transverse momentum distributions of hadrons produced in neutrino-nucleon charged current interactions and their dependence onW are analysed in detail. It is found that the components of the transverse momentum in the event plane and normal to it increase withW at about the same rate throughout the availableW range. A comparison withe ⁺ e ^? data is made. Studies of the energy flow and angular distributions in the events classified as planar do not show clear evidence for high energy, wide angle gluon radiation, in contrast to the conclusion of a previous analysis of similar neutrino data.