Experience with a toroidal proportional detector for backscattered Mössbauer ψ-rays and X-rays

Because backscattering geometry in Mössbauer spectroscopy is particularly useful for non-destructive testing interesting technical applications arise. The reported toroidal proportional detector for backscattered Mössbauer ψ-rays and X-rays enables non-destructive testing of technical surfaces since no sample preparation is required. Improvements in assembling, shielding, wire-fixing and gas-filling-in comparison to the first version of the detector-are reported. The performance of the improved detector is demonstrated by measurements of steel surfaces which are modified by plasma nitriding and laser irradiation.     

Zur Theorie der strahlungslosen Energierelaxation vieler miteinander wechselwirkender Molekülnormalschwingungen

Theory of Radiationless Energy Relaxation of a Large Number of Coupled Molecular Normal Vibrations On the base of a general relaxation theory recently developed by the authors the dissipation and transfer of energy in a system of a large number of coupled molecular vibrations are studied. Especially, vibrations of the same kind belonging to molecules localized at different space points of a dense medium are considered. For a short-range and a long-range interaction potential time-dependent generalized damping parameters are calculated, which give rise to non-exponential decay laws for the vibrational energy of the molecules.     

Stokes and anti-stokes linewidths in a solid state anti-stokes Raman oscillator

By using quantum mechanical Langevin equations the linewidths of Stokes and anti-Stokes modes are calculated as functions of damping, pumping, and detuning.     

Excitons in artificial quantum dots in the weak spatial confinement regime

The exciton states in individual quantum dots prepared by the selective interdiffusion method in CdTe/CdMgTe quantum wells are studied by the methods of steady-state optical spectroscopy. The annealing-induced diffusion of Mg atoms inward to the bulk of the quantum well, which is significantly enhanced under the SiO₂ mask, leads to a modulation of the bandgap width in the plane of the well, with the minima of the potential being located in the mask aperture areas. A lateral potential that arises, whose height is in the range 30–270 meV and characteristic scale is about 100 nm, efficiently localizes carriers, which form quasi-zero-dimensional excitons in the weak spatial confinement regime. Detailed magnetooptical studies show that Coulomb correlations play a significant role in the formation of exciton states under such a regime, which, in particular, manifests itself in the localization of the wavefunction of carriers on scales that are considerably smaller than the scale of the lateral potential. The particular features of the interlevel splitting, of the biexciton binding energy, and of the diamagnetic shift are discussed. A strong dependence of the interlevel relaxation on the interlevel splitting (the phonon neck) indicates that alternative relaxation mechanisms in the quantum dots studied are weak. The excited states are populated according to the Pauli principle, which indicates that it is possible to apply the shell model of many-exciton states to quantum dots under the weak spatial confinement conditions.     

Intensity correlation spectroscopy of the resonance fluorescence light of two-atomic molecules

The spectroscopic application of intensity correlation measurements of the resonance fluorescence light from two-atomic molecules is proposed. It is shown that from the intensity correlation function not only the natural line width of the electronic transition and the electron-vibration coupling strength but also very narrow homogeneous vibrational line widths can be determined without any use of a spectral apparatus.     

Struktur‐ und magnetochemische Untersuchungen an Ba5Mn3F19 und verwandten Verbindungen AII5MIII3F19

Structural and Magnetochemical Studies of Ba₅Mn₃F₁₉ and Related Compounds A^II₅M^III₃F₁₉ Single crystal structure determinations by X‐ray methods were performed at the following compounds, crystallizing tetragonally body‐centred (Z = 4): Sr₅V₃F₁₉ (a = 1423.4(2), c = 728.9(1) pm), Sr₅Cr₃F₁₉ (a = 1423.5(2), c = 728.1(1) pm), Ba₅Mn₃F₁₉ (a = 1468.9(1), c = 770.3(1) pm, Ba₅Fe₃F₁₉ (a = 1483.5(1), c = 766.7(1) pm), and Ba₅Ga₃F₁₉ (a = 1466.0(2), c = 760.1(2) pm). Only Ba₅Mn₃F₁₉ was refined in space group I4cm (mean distances for elongated octahedra Mn1–F: 185/207 pm equatorial/axial; for compressed octahedra Mn2–F: 199/182 pm), the remaining compounds in space group I4/m. In all cases the octahedral ligand spheres of the M1 atoms showed disorder, the [M1F₆] octahedra being connected into chains in one part of the compounds and into dimers in the other. The magnetic properties of the V, Cr and Mn compounds named above and of Pb₅Mn₃F₁₉ and Sr₅Fe₃F₁₉ as well were studied; the results are discussed in context with the in part problematic structures.     

Preparation of On-Column Frits in Packed Fused Silica Capillaries by Sol-Gel Technology

Existing methods for preparing frits in packed fused silica capillaries as used for electrochromatography and micro HPLC are not applicable to all silica based packing materials and involve a high thermal stress for both the stationary phase and the fused silica tubing including the polyimide coating. A new procedure for the production of such on-column frits under mild conditions by a sol-gel type reaction of polydimethoxysiloxane (PDMOS) is described in this paper. Reaction conditions were established for optimum mechanical stability and high permeability of the frits. Frits produced in this manner showed no noticeable effect on the overall efficiency.