Investigation of the threshold effects by a soluble two-channel model its application to hyperon-nucleon scattering

Threshold effects are studied by a soluble two-channel model with separable interactions. The optimal conditions for a considerable threshold effect are indicated. The general formalism is applied to the hyperon-nucleon scattering problem investigating the cross sections for coupledΛN andΣN channels near theΣN threshold.     

A Three-body model for the study of resonance phenomena. III

The potential and quasi-compound resonances appearing in a model three-body system consisting of two identical light particles and an infinitely heavy one is investigated by solving the Faddeev-equations for negative total energy.     

Combined DTA and XRD Study of Sintering Steps Towards YAl3(BO3)4

Sintering processes in the Y₂O₃–Al₂O₃–B₂ O₃ system and its subsystems (Y₂O₃–B₂O₃ and Al₂ O₃–B₂O₃) have been investigated by using combined DTA and XRD measurements to get a better understanding of solid state chemical changes resulting in the formation of yttrium aluminum borate (YAl₃(BO₃)₄, YAB) phase and to study the possible role and contribution of various simple borates formed also in the former processes. Two new exothermic heat effects of YBO₃ formation have been detected by DTA in the Y₂O₃–B₂O₃ system between 720 and 980°C. In the Al₂O₃–B₂O₃ system a new experimental XRD profile of Al₄B₂O₉ was observed. Formation of these borates seems to promote the nucleation of double borate YAB below 1000°C. Conversion of Al₄B₂O₉ to Al₁₈B₄ O₃₃ was observed after a long term (10 h) sintering at 1050°C. Similarly, an increased formation of YAB has been observed as a product of the sintering reaction between YBO₃ and Al₁₈B₄O₃₃ at 1150°C. The two latter single borates are found to be identical with the high temperature decomposition products of YAB. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dissolution forms of rare-earth gallium-aluminium garnets

Acta Physica Hungarica - Single crystal spheres of rare-earth gallium-aluminium garnet crystals (R3Al5?x Ga x O12, whereR=rare-earths and 0≤x≤5) have been dissolved in H3PO4 and...     

Infrared absorption spectra of pure and doped YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> single crystals

Several weak absorption bands have been observed in the optical absorption spectra of pure and rare-earth-doped YAl₃(BO₃)₄ single crystals in the 3350– 3650 cm⁻¹ wave number region. Two of them, peaking at about 3377 cm⁻¹ and 3580 cm⁻¹ in the 8 K spectra, appear in most of the samples. They are tentatively attributed to the stretching mode of OH⁻ ions incorporated in the crystal during the growth. An additional absorption band at about 5250 cm⁻¹ at 8 K has also been detected in almost all samples. The temperature and polarization dependences of these bands, and their possible origin, are discussed.     

A three-body model for the study of resonance phenomena

A three-body model suitable for the investigation of compound, quasi-compound and potential resonances is presented. The exact solution of the model based on Faddeev's method is discussed. Numerical calculations are performed for negative total energy.     

Spectroscopic analysis of Pr<Superscript>3+</Superscript> crystal-field transitions in YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>

Yttrium aluminium borate single crystals, doped with 1 and 4 mol% of Pr³⁺, were analyzed in the wave number range 500–25000 cm⁻¹ and temperature range 9–300 K by means of high-resolution Fourier transform spectroscopy. In spite of the complex spectra, exhibiting broad and split lines, the energy level scheme was obtained for several excited manifolds. The careful analysis of the spectra as a function of the temperature allowed us to identify most of the sublevels of the ground manifold. The thermally induced line shift, well described by a single-phonon coupling model, could be exploited to provide information about the energy of the phonons involved. The orientation of the dielectric ellipsoid and of the dipole moments associated to a few transitions was also determined from linear dichroism measurements. The experimental data were fitted in the framework of the crystal-field theory, but the agreement was not satisfactory, as already reported for Pr³⁺ ion in other matrices. Additional discrepancies came from the dichroic spectra analysis and the line splitting, possibly associated to hyperfine interaction. Some causes which might be responsible for the difficulties encountered in the Pr³⁺ ion theoretical modelling are discussed.     

Growth and Spectroscopic Properties of Er:Yab Single Crystals

The Er-doped YAB (YAl₃(BO₃)₄) is a potential self-frequency-doubling laser material. Single crystals were grown by the top-seeded flux method. The absorption spectra of the infrared Er^3? transitions were monitored in YAB crystals in the 9–300 K temperature range by high-resolution Fourier transform spectroscopy. In the whole spectral range the energy levels and Stark components of 12 transitions were detectable. In this paper the two infrared transitions (from the ⁴I_15/2 ground state to the ⁴I_13/2 and ⁴I_11/2 levels) were analyzed in detail. The low temperature absorption spectra of Er:YAB consist of sharp lines, the number of which corresponds to the theoretical predictions. This suggests that Er^3? ions occupy one specific lattice site (yttrium positions) with negligible aggregation at the higher dopant concentrations investigated (i.e. 0.12 Fr atom/YAB mole).     

Effect of temperature on luminescence and VUV to visible conversion in the YAl3(BO3)4:Dy (YAB:Dy) crystal

Spectroscopic properties of the Dy³⁺-doped YAl₃(BO₃)₄ crystal were studied from the vacuum-ultraviolet to near-infrared spectral range. Optical results were interpreted in terms of the 4fⁿ, 4fⁿ⁻¹5d and charge transfer transitions. It was found that the VUV electronic excitation is transferred to the optically active ions giving emission from the ⁴F_9/2 fluorescent level of Dy³⁺. The temperature variation of the Dy³⁺ fluorescence kinetics was observed; the ⁴F_9/2 lifetime increased with increasing temperature. This phenomenon is not usually observed in other rare-earth-doped media. The discussion of dysprosium emission properties and their temperature dependency was based on the assumption that the rates of transitions originating in individual crystal field levels of the ⁴F_9/2 emitting multiplet are significantly different.     

Sc-Ion distribution and dissolution forms of ScGaYIG single crystals

Acta Physica Hungarica - Single crystal spheres of Y3Fe4, 2−xGa0,8Scx012, where 0≤x≤1, 45, have been dissolved in acids and measured by Mössbauer and IR methods. It was...