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Role of Correlations and Off-Diagonal Terms in Binary Disordered One-Dimensional Systems

100%

Kosior A., Major J., Płodzień M., Zakrzewski J.

Acta Physica Polonica A

2015

vol. 128

issue 6

1002-1007

We investigate one-dimensional tight binding model in the presence of a correlated binary disorder. The disorder is due to the interaction of particles with heavy immobile other species. Off-diagonal disorder is created by means of a fast periodic modulation of interspecies interaction. The method based on transfer matrix techniques allows us to calculate the energies of extended modes in the correlated binary disorder. We focus on N-mer correlations and regain known results for the case of purely diagonal disorder. For off-diagonal disorder we find resonant energies. We discuss ambiguous properties of those states and compare analytical results with numerical calculations. Separately we describe a special case of the dual random dimer model.

The Kinetics of the Spin-Conversion of Positronium Measured by β^{+}γ∆E Age-Momentum Correlation

64%

Lauff U., Maier K., Major J., Seeger A., Stoll H., Wesołowski P., Koch M., Bilard I., Abbé J., Duplâtre G.

Acta Physica Polonica A

1993

vol. 83

issue 3

349-358

Age-momentum correlation (AMOC) measurements provide time-resolved information on the momentum distribution of annihilating electron-positron pairs through correlated determination of Doppler broadening (∆E) of the 511 keV annihilation radiation line and positron age. In the β^{+}γ∆E AMOC technique implemented at the Stuttgart pelletron accelerator the start signals for the age measurements are generated when the relativistic positrons pass through a fast plastic scintillator, which has a detection efficiency close to unity. Beam-based β^{+}γ∆E AMOC measurements thus combine high β^{+}γ∆E triple-coincidence rates with low background. From a practical point of view this constitutes a major progress compared to conventional (source-based) γγ∆E AMOC measurements. The AMOC technique permits direct access to a wide variety of time-dependent processes, among them the reaction kinetics in positronium chemistry. As an example, we present a β^{+}γ∆E AMOC investigation of the kinetics of a spin-conversion reaction of positronium in methanol induced by the presence of a nitrosyl free-radical paramagnetic solute (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl , HTEMPO). The AMOC measurements allowed the time-resolved observation of the spin-conversion process, which had been investigated before by uncorrelated positron lifetime and Doppler-broadening measurements. It is found that within the concentration range investigated (≤ 0.1 mol/l) the spin-conversion reaction rate at room temperature depends linearly on the HTEMPO concentration with a reaction-rate constant k_{conv} = (22.5 ± 0.5) × 10^{9} l mol^{-1} s^{-1}.

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2 Acta Physica Polonica A

1 2015

1 1993

2 Major J.

1 Abbé J.

1 Bilard I.

1 Duplâtre G.

1 Koch M.

1 Kosior A.

1 Lauff U.

1 Maier K.

1 Płodzień M.

1 Seeger A.

1 Stoll H.

1 Wesołowski P.

1 Zakrzewski J.

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Role of Correlations and Off-Diagonal Terms in Binary Disordered One-Dimensional Systems

The Kinetics of the Spin-Conversion of Positronium Measured by β^{+}γ∆E Age-Momentum Correlation