25 research outputs found
Quantum spin pumping with adiabatically modulated magnetic barrier's
A quantum pump device involving magnetic barriers produced by the deposition
of ferro magnetic stripes on hetero-structure's is investigated. The device for
dc- transport does not provide spin-polarized currents, but in the adiabatic
regime, when one modulates two independent parameters of this device, spin-up
and spin-down electrons are driven in opposite directions, with the net result
being that a finite net spin current is transported with negligible charge
current. We also analyze our proposed device for inelastic-scattering and
spin-orbit scattering. Strong spin-orbit scattering and more so inelastic
scattering have a somewhat detrimental effect on spin/charge ratio especially
in the strong pumping regime. Further we show our pump to be almost noiseless,
implying an optimal quantum spin pump.Comment: 14 pages, 9 figures. Manuscript revised with additional new material
on spin-orbit scattering and inelastic scattering. Further new additions on
noiseless pumping and analytical results with distinction between weak and
strong pumping regimes. Accepted for publication in Physical Review
Measurement Of The Σ̄- Lifetime And Direct Comparison With The Σ+ Lifetime
We have measured the lifetime of the Σ̄- using the Fermilab Proton Center 375 GeV/c charged hyperon beam. We obtained (80.43±0.80±0.14) ps. We also measured the lifetime of the Σ+, obtaining (80.38 ±0.40±0.14) ps, in agreement with the Particle Data Group value. A direct comparison between the two lifetimes from the ratio of the decay curves gives a fractional lifetime difference of Δτ/τ=(-0.06±1.12)%, consistent with equal lifetimes for baryon and antibaryon as required by CPT invariance. ©1999 The American Physical Society.61314Foucher, M., (1992) Phys. Rev. Lett., 68, p. 3004Timm, S., (1995) Phys. Rev. D, 51, p. 4638Dubbs, T., (1994) Phys. Rev. Lett., 72, p. 808Caso, C., (1998) Eur. Phys. J. C, 3, p. 690(1993) GEANT 3.21 CERN Program Library W5103, , CERNKuropatkin, N., private communicationLangland, J.L., (1995) Hyperon and Antihyperon Production in P-Cu Interactions, , Ph.D. thesis, University of IowaMorelos, A., (1993) Phys. Rev. Lett., 71, p. 341
Photoconductivity of nanocrystalline <tex>SnO_{2}$</tex> sensitized with colloidal CdSe quantum dots
Nuclear-matter distributions of halo nuclei from elastic proton scattering in inverse kinematics
Proton-nucleus elastic scattering at intermediate
energies, a well-established method for probing nuclear-matter density
distributions of stable nuclei, was applied for the first time to exotic
nuclei. This method is demonstrated to be an effective means for obtaining
accurate and detailed information on the size and radial shape of halo
nuclei. Absolute differential cross-sections for small-angle scattering were
measured at energies near 700 MeV/u for the neutron-rich helium isotopes
\chem{^{6}He} and \chem{^{8}He}, and more recently for the lithium isotopes
\chem{^{6}Li}, \chem{^{8}Li}, \chem{^{9}Li} and \chem{^{11}Li}, using He and Li beams
provided by the fragment separator FRS at GSI Darmstadt. Experiments were
performed in inverse kinematics using the hydrogen-filled ionization chamber
IKAR which served simultaneously as target and recoil-proton detector.
For deducing nuclear-matter distributions, differential cross-sections
calculated with the aid of the Glauber multiple-scattering theory, using
various parametrizations for the nucleon density distributions as input,
were fitted to the experimental cross-sections. The results on nuclear-matter radii and matter distributions are presented, and the significance of
the data for a halo structure is discussed. Nuclear-matter distributions
obtained for \chem{^{6}He} and \chem{^{8}He} conform with the concept that both
nuclei compose of -particle like cores and significant neutron
halos. The matter distribution in \chem{^{11}Li} exhibits, as expected from
previous reaction cross-section studies with nuclear targets, the by far
most extended halo component of all nuclei being investigated. In addition
the present data allow a quantitative comparison of the structure of the He
and Li isobares of either the mass number or . The measured
differential cross-sections have also been used for probing density
distributions as predicted from various microscopic calculations. A few
examples are presented
Halo structure of 8B determined from intermediate energy proton elastic scattering in inverse kinematics
The absolute differential cross section for small-angle proton elastic scattering on the proton-rich 8B nucleus has been measured in inverse kinematics for the first time. The experiment was performed using a secondary radioactive beam with an energy of 0.7 GeV/u at GSI, Darmstadt. The active target, namely hydrogen-filled time projection ionization chamber IKAR, was used to measure the energy, angle and vertex point of the recoil protons. The scattering angle of the projectiles was simultaneously determined by the tracking detectors. The measured differential cross section is analyzed on the basis of the Glauber multiple scattering theory using phenomenological nuclear-density distributions with two free parameters. The radial density distribution deduced for 8B exhibits a halo structure with the root-mean-square (rms) matter radius Rm=2.58(6) fm and the rms halo radius Rh=4.24(25) fm. The results on 8B are compared to those on the mirror nucleus 8Li investigated earlier by the same method. A comparison is also made with previous experimental results and theoretical predictions for both nuclei. Keywords: 8B, Proton halo, Proton elastic scattering, Inverse kinematic