Studying the possibility of deep laser cooling of <Superscript>24</Superscript>Mg atoms in an optical lattice: Two-level quantum model

The possible deep laser cooling of ²⁴Mg atoms in a deep optical lattice in the presence of an additional pumping field resonant to the narrow 3s3s¹S₀ → 3s3p³P₁ (λ = 457 nm) optical transition is studied. Two quantum models of the laser cooling of atoms in the optical trap are compared. One is based on the direct numerical solution to the kinetic quantum equation for an atomic density matrix; it considers both optical pumping and quantum recoil effects during interaction between the atoms and field photons. The second, simplified model is based on decomposing the states of the atoms over the levels of vibration in the optical trap and analyzing the evolution of these states. The comparison allows derivation of optical field parameters (pumping field intensity and detuning) that ensure cooling of the atoms to minimal energies. The conditions for fast laser cooling in an optical trap are found.     

Secondary ion emission from a GaAs single crystal upon bombardment with Bi<Stack> <Subscript> <Emphasis Type="Italic">m</Emphasis> </Subscript> <Superscript>+</Superscript> </Stack> cluster ions

Secondary-ion mass spectra and energy distributions upon bombarding a gallium arsenide single crystal using Bi_m⁺(m = 1–5) cluster ions with energies of 2–12 keV are investigated. The gallium cluster ion yield grew nonadditively with the number of atoms in the cluster projectiles. A quasi-thermal component found in the energy spectra of secondary Ga⁺ and Ga₂⁺ ions is indicative of the occurrence of the thermal spike mode upon cluster ion bombardment. The quasi-thermal component in the yield of atomic Ga⁺ ions upon bombardment with Bi₂⁺–Bi₅⁺–ions is 35–75%.     

X-ray photoelectron spectroscopy of FeP phosphide

The structure of the outer and inner electron spectra of iron (2p, 3p, 3s, and 3d) and phosphorus (3s and 3p) atoms in FeP monophosphide is studied in detail by the X-ray photoelectron spectroscopy (XPS) method. On the basis of the analysis of the binding energy of electrons, as well as the parameters characterizing the structure of experimental spectra, a conclusion is made that Fe³⁺ (d ⁵) cations in FeP are stabilized in a state with intermediate value of the total spin (IS, S = 3/2). The range of values of intra-atomic parameters (10Dq, J _H ) is established in which the consideration of the high degree of covalence of Fe–P bonds may lead to the stabilization of (FeP₆)^15– clusters in the IS state.     

Die Spektren der Neutronen aus den Reaktionen C12(γ,n)C11 und O16(γ,n)O15

The (γ, n)-reactions on carbon and oxygen were studied using the 30,5 MeV brems-strahlung beam of the Heidelberg betatron. The photoneutrons were detected via the recoil protons in a stilbene scintillator. The pulse height spectrum of scintillations produced in the stilbene crystal by the recoil protons is analyzed to yield the incident neutron energy distribution. Theγ-ray and electron background was strongly reduced through pulse shape discrimination. To test the apparatus the spectrum of the neutrons from a Po-α-Be source was measured. The energy spectrum of the photo-neutrons from O¹⁶ shows clearly two peaks at excitation energies of 22,4 and 24,4 MeV also seen in the photo-proton spectra. The energy distribution of the neutrons from C¹² (γ, n) too contains indication of structure already known from the proton spectra from C¹² (γ, p). The derived cross sections of C¹² (γ, n ₀) and O¹⁶ (γ, n ₀) coincide as well in their shape as in their absolute magnitude with the corresponding (γ, p ₀)-cross sections. In both C¹² (γ, n) and O¹⁶ (γ, n)-reaction the neutrons seem to leave the final nucleus mainly in its ground state.     

The Rank-One Separable Interaction Kernel for Nucleons with Scalar Propagator

In the paper the covariant kernel of the nucleon-nucleon interaction of particles with scalar propagators is analyzed. The Bethe–Salpeter equation for the T matrix is considered in the rank-one separable kernel. The parameters of the kernel for the specific partial-wave channels explicitly connect with the observables low energy scattering parameters and phase shifts, deuteron binding energy. Covariant separable kernels for the partial-wave channels with total angular momentum J = 0 (¹S₀, ³P₀) and J =1 (³S₁ ? ³D₁, ¹P₁, ³P₁) are constructed.     

Photoluminescence of Ca(Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>S<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript> compounds

Photoluminescence (PL) observed in solid solutions of Ca(Al _x Ga_1–x )₂S₄:Eu²⁺ (x = 0.1–0.3) is studied. It is shown that the increase in emission intensity by 18% is caused by changes in the x values and electronic 5d → 4 f transitions in Eu²⁺ ions. A change in the position of the emission spectrum or its partial shift toward shorter wavelengths is due to an increase in the aluminum concentration and a decrease in the crystal field energy. The energy of the zero phonon line E ₀, redshift D, and the Stokes shift ΔS are determined. A decrease in the photoluminescence intensity maximum and an increase in the half-width of the spectrum are found in the temperature range of 10–300 K. The efficiency of emission at temperatures of 20 and 300 K is almost independent of the excitation power density of up to ~10⁴ W/cm². The luminescence lifetime of Eu²⁺ ions was 383, 357, 346, and 333 ns for x = 0, 0.1, 0.2, and 0.3, respectively.     

Thermodynamic study of compounds of the Nd-Ba-Cu-O system

Standard enthalpies of formation for solid solutions of composition Nd_{1 + x} Ba_{2 ? x} Cu₃O _y (x = 0–0.8, y = 6.65–7.24) from oxides were determined by solution calorimetry. The heat capacity of NdBa₂Cu₃O_6.87 phase was measured in the range 5–320 K by low-temperature adiabatic calorimetry. The absolute entropy S ^o(T), the difference of enthalpies H ^o(T)-H ^o(0 K), and the reduced Gibbs energy Φ^o(T) = S ^o(T)–[H ^o(T)–H ^o(0)]/T were calculated on the basis of smoothed dependence C _p (T) in the 0–320 K range. An assessment was made for the heat capacities and the absolute entropies of solid solutions Nd_1+x Ba_2?x Cu₃O _y . The obtained set of thermodynamic parameters can be used for the calculation of phase equilibria in the Nd-Ba-Cu-O system.     

Role of structure imperfection in the formation of the magnetotransport properties of rare-earth manganites with a perovskite structure

The structure, the structure imperfection, and the magnetoresistance, magnetotransport, and microstructure properties of rare-earth perovskite La_0.3Ln_0.3Sr_0.3Mn_1.1O_3–δ manganites are studied by X-ray diffraction, thermogravimetry, electrical resistivity measurement, magnetic, ⁵⁵Mn NMR, magnetoresistance measurement, and scanning electron microscopy. It is found that the structure imperfection increases, and the symmetry of a rhombohedrally distorted R3?c perovskite structure changes into its pseudocubic type during isovalent substitution for Ln = La³⁺, Pr³⁺, Nd³⁺, Sm³⁺, or Eu³⁺ when the ionic radius of an A cation decreases. Defect molar formulas are determined for a real perovskite structure, which contains anion and cation vacancies. The decrease in the temperatures of the metal–semiconductor (T _ms) and ferromagnet–paramagnet (T _C) phase transitions and the increase in electrical resistivity ρ and activation energy E _a with increasing serial number of Ln are caused by an increase in the concentration of vacancy point defects, which weaken the double exchange 3d ⁴(Mn³⁺)–2p ⁶(O^2–)–3d ³(Mn⁴⁺)–V ^(a)–3d ⁴(Mn³⁺). The crystal structure of the compositions with Ln = La contains nanostructured planar clusters, which induce an anomalous magnetic hysteresis at T = 77 K. Broad and asymmetric ⁵⁵Mn NMR spectra support the high-frequency electronic double exchange Mn³⁺(3d ⁴) ? O^2–(2p ⁶) ? Mn⁴⁺(3d ³) and indicate a heterogeneous surrounding of manganese by other ions and vacancies. A correlation is revealed between the tunneling magnetoresistance effect and the crystallite size. A composition–structure imperfection–property experimental phase diagram is plotted. This diagram supports the conclusion about a strong influence of structure imperfection on the formation of the magnetic, magnetotransport, and magnetoresistance properties of rare-earth perovskite manganites.     

Specific features of the three-electron <Emphasis Type="Italic">KL</Emphasis><Stack><Subscript>2, 3</Subscript><Superscript>2</Superscript></Stack> ionization of silicon atoms upon near-threshold photoabsorption

The shape and relative intensity of the group of the Kα_5–8 satellites (radiative transitions KL _{2, 3} ² )-L _{2, 3} ³ of Si atoms are experimentally studied upon photoabsorption near and far from the KL _{2, 3} ² ionization threshold. The satellites were excited near the ionization threshold by lines of the characteristic L spectrum and bremsstrahlung radiation from Nb and Mo anodes and far from the threshold by the L spectrum and bremsstrahlung radiation from an Ag anode and by monochromatized Kα_{1, 2} radiation from a Ti anode. It is established that the probability P(L _{2, 3} ² ) of formation of two additional 2p vacancies during KL _{2, 3} ² photoabsorption of Si atoms near the energy threshold is by a factor of 1.5 lower than that during photoionization in a more distant energy region beyond the threshold. At the same time, the P(L _{2, 3} ² )/P(L _{2, 3}) ratio remains invariable for the absorbed photons throughout the energy range studied. It is demonstrated that, as the KL _{2, 3} ² ionization threshold is approached, an intensity redistribution occurs among the components of the group of the Kα_5–8 lines, which reflects a decrease in the excitation cross section ratio σ(⁴ P)/σ(² P) of the ⁴ P and ² P terms of the KL _{2, 3} ² configuration. A conclusion is drawn that the effects of suppression of the generation of P terms of higher multiplicity during the KL _{2, 3} and KL _{2, 3} ² near-threshold photoionizations are of a common nature.     

Distant metagalactic sources of very high energy γ rays: 1739 + 522 and 3c454.3

Sources with red shifts from z = 0.0179 to 1.375 have been observed with the SHALON telescope. Fluxes, spectral energy distributions, integrated spectra, and images of new (in the TeV energy range) distant sources—flat-spectrum radio quasars 1739 + 522 and 3c454.3—are reported. It is shown that the energy spectrum of metagalactic sources (Mkn421 and Mkn501 quasars) in the energy range 10¹²–10¹³ eV in the power-law representation differs from the spectrum of 1739 + 522 and 3c454.4 distant quasars, which do not contradict the unified energy spectrum F(>E) ～ E _γ ^?1.26±0.15 .     

Angular correlation measurements in the Be9(d,p, γ)Be10 reaction

Thep-γ angular correlations in the Be⁹(d, p, γ)Be¹⁰ reaction have been measured in the reaction plane atE _d =1.3, 1.5, 1.9, 2.3 and 2.45 MeV for proton anglesθ _p =35°, 80° and 120°. The anisotropy of the angular correlations measured forθ _p =35° is independent of deuteron energy. A systematic shift of the symmetry axis from the recoil direction has been observed. The shift is 20.5° at E_d=2.45 MeV. The anisotropy decreases with increasing proton angle and vanishes atθ _p =120°.     

Hyperfine structure of the <Emphasis Type="Italic">S</Emphasis> levels of the muonic helium ion

Corrections of the α⁵ and α⁶ orders to the energy spectrum of the hyperfine splitting of the 1S and 2S levels of the muonic helium ion are calculated with the inclusion of the electron vacuum polarization effects, nuclear-structure corrections, and recoil effects. The values ΔE ^hfs(1S) = ?1334.56 meV and ΔE ^hfs(2S) = ?166.62 meV obtained for hyperfine splitting values can be considered as reliable estimates for comparison with experimental data. The hyperfine structure interval Δ₁₂ = 8ΔE ^hfs(2S) ? ΔE ^hfs(1S) = 1.64 meV can be used to verify QED predictions.     

Level structure of <Superscript>164</Superscript>Dy from the (<Emphasis Type="Italic">n</Emphasis>, <Emphasis Type="Italic">n</Emphasis>′γ) reaction

By employing a beam of reactor fast neutrons, gamma-ray spectra and angular distributions of gamma rays with respect to the neutron-beam axis were measured in the reaction ¹⁶⁴Dy(n, n′γ). The scheme of levels and gamma transitions in ¹⁶⁴Dy was composed on the basis of data published earlier and new levels, rotational bands, gamma transitions, and multipole-mixing parameters. It is concluded that the scheme of J = 0–4 levels is complete up to the excitation energy of 1.95 MeV. The commonly accepted rule in constructing K _n ^π = 0₂ ⁺ and 1₁ ⁺ rotational bands is found to be violated. The nature of the 2⁺ level at the energy of 1796.68 keV is discussed.     

Mictomagnetic State in an EuBaCo<Subscript>2–<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>5.5–δ</Subscript> Single Crystal

The magnetic properties of an EuBaCo_1.9O_5.36 single crystal are studied in the temperature range T = 2–300 K and the magnetic field range H ≤ 90 kOe. This binary layered cobaltite single crystal has vacancies in the cobalt and oxygen sublattices, in contrast to the stoichiometric EuBaCo₂O_5.5 composition. All cobalt ions in EuBaCo1.9O5.36 are in a trivalent state. The single crystal has an orthorhombic structure with space group Pmmm, and its unit cell parameters are a = 3.883 Å, b = 7.833 Å, and c = 7.551 Å. The field and temperature dependences of the magnetization of the single crystal demonstrate that it is ferrimagnet below T_C = 242 K. At T < 300 K, all three spin states of the Co³⁺ ions are present. The nearest-neighbor interactions give antiferromagnetic (AFM) and ferromagnetic (FM) contributions to the exchange energy. The ratio of the AFM to the FM contributions changes when temperature decreases because of a change in the spin state of the Co³⁺ ions. The single crystal exhibits signs of mictomagnetism at low temperatures in high magnetic fields. At T = 2 K and H = 90 kOe, the zero-field and nonzero-field magnetizations are strongly different because of a uniaxial magnetic anisotropy, which tends to set magnetization along the magnetic field applied in cooling throughout the crystal volume. As a result, a complex ferrimagnetic structure with a noncollinear direction of Co³⁺ spins appears. The following phenomena characteristic of mictomagnets are also observed in the EuBaCo_1.9O_5.36 single crystal: a shift in a magnetization hysteresis loop when temperature decreases, retained hysteretic phenomena and no magnetization saturation in high magnetic fields, and an orientation transition. The mictomagnetic state in EuBaCo_1.9O_5.36 is shown to be caused by the structural distortions induced by vacancies in the cobalt and oxygen sublattices and by the frustration of AFM and FM exchange interactions.     

Spectra of optical absorption and energy levels diagram of Er<Superscript>3+</Superscript> ions in bulk crystals of aluminum nitride

The absorption spectra of the Er³⁺ ions embedded in the AlN matrix have been investigated. The admixture of erbium was introduced in bulk AlN crystals by diffusion. The absorption lines, which are associated with the intraconfigurational electronic f–f-transitions from the ground ⁴ I _15/2-state to the levels of ion Er³⁺ excited states have been observed in the spectral range of 370–700 nm. The transitions to the state levels ⁴ F _9/2, ² H _11/2, ⁴ F _7/2, ⁴ F _5/2, ² H _9/2, and ⁴ G _11/2 have been investigated in detail at the temperature T = 2 K. The number of the observed lines for these transitions coincides with the theoretically possible one for the electronic f–f-transitions in the ions Er³⁺, which are in the crystal field with the symmetry below cubic. The narrowness of the observed lines and their number convincingly testify the replacement of preferably one regular crystalline position by erbium ions. The implementation of Er³⁺ in the Al³⁺ position with the local symmetry C _3v appears the most probable. The energy positions of the levels of excited states for the investigated transitions have been determined. The diagram of the Er³⁺ ion energy levels in the AlN crystals has been built.     

Magnetostriction of Hexagonal HoMnO<Subscript>3</Subscript> and YMnO<Subscript>3</Subscript> Single Crystals

We report on the magnetostriction of hexagonal HoMnO₃ and YMnO₃ single crystals in a wide range of applied magnetic fields (up to H = 14 T) at all possible combinations of the mutual orientations of magnetic field H and magnetostriction ΔL/L. The measured ΔL/L(H, T) data agree well with the magnetic phase diagram of the HoMnO₃ single crystal reported previously by other authors. It is shown that the nonmonotonic behavior of magnetostriction of the HoMnO₃ crystal is caused by the Ho³⁺ ion; the magnetic moment of the Mn³⁺ ion parallel to the hexagonal crystal axis. The anomalies established from the magnetostriction measurements of HoMnO₃ are consistent with the phase diagram of these compounds. For the isostructural YMnO₃ single crystal with a nonmagnetic rare-earth ion, the ΔL/L(H, T) dependences are described well by a conventional quadratic law in a wide temperature range (4–100 K). In addition, the magnetostriction effect is qualitatively estimated with regard to the effect of the crystal electric field on the holmium ion.     

The effect of high pressure on the structure and on the magnetic and electronic properties of nickel monoxide

A diamond anvil cell is used to investigate the effect of high pressure (up to 37.5 GPa) on the optical absorption spectra of a single crystal of nickel oxide (NiO). In addition, strain-gage measurements are used to experimentally investigate the V(P) equation of state at a hydrostatic pressure of up to 8.5 GPa in a high-pressure chamber of the “toroid” type. Measurements are performed at room temperature. Absorption bands are observed, which correspond to optical d-d transitions of Ni²⁺ ion in the crystal field of ligands ³A_2g → ³T_2g, ³A_2g → {au1}E_1g, ³A_2g → ³T_1g(F), and ³A_2g → ¹T_2g. The values of energy of these transitions increase linearly with pressure, and their pressure coefficients are 7.3 ± 0.2, 2.87 ± 0.9, 9.7 ± 0.5, and 8.9 ± 0.3 meV/GPa, respectively. The pressure derivative of the crystal field parameter 10Dq corresponding to the ³A_2g → ³T_2g transition gives the pressure dependence of the magnitude of exchange integral J in the Anderson hybridization model. It is found that, in the pressure range from zero to 37.5 GPa, the behavior of the exchange integral J is largely defined by the hybridization parameter b = (10Dq/3). At the same time, the Coulomb interaction parameter U_eff is independent of pressure and, therefore, has no effect on the variation of J. The Coulomb interaction U_eff ≈ 7.47 ± 0.005 eV is determined. The experimental data on the equation of state are used to derive the \(J \propto V^\varepsilon \) correlation, where ε = ?2.99 ± 0.15, which is in good agreement with the predictions of Bloch’s theory (ε = ?10/3).     

On the size dependence of melting parameters for silicon

Using the dependences of melting point T_m and crystallization point T_c on the number of atoms (N) in a spherical silicon crystal that were calculated elsewhere [6] by the method of molecular dynamics, (i) the number of atoms at which the latent heat of the solid–liquid phase transition disappears and (ii) temperature T₀ = T_m(N₀) = _Tc(N₀) below which solidifying nanoclusters remain noncrystalline are estimated. These values are found to be N₀ = 22.8156 and T₀ = 400.851 K. The N dependences for silicon melting parameters, namely, a jump of entropy of melting, latent melting heat, slope of the melting line, and jumps in the surface energy and volume, are derived.     

Recombination population of excited states of the hydrogen atom in an He-H<Subscript>2</Subscript> plasma

The population of excited states of the hydrogen atom in an afterglow plasma produced by a pulsed discharge in helium (40 Torr) with a small admixture of hydrogen ([H₂] ≈ 10¹² cm^?3) has been studied spectroscopically. The contribution from electron-ion recombination Γ ₃ ^rec to the production rate of atoms H(n = 3) has been separated. On the basis of an experiment in which the response of the spectral line intensities to the perturbation of the electron temperature in the afterglow phase was observed, the dependence Γ ₃ ^rec (T _e ～ T _e ^?(0.9–1.0) has been obtained in the region kT _e = 0.026–0.064 eV.