Search results for "POLARIZATION"
showing 10 items of 1884 documents
Magnetic resonance imaging of (1)H long lived states derived from parahydrogen induced polarization in a clinical system.
2015
Hyperpolarization is a powerful tool to overcome the low sensitivity of nuclear magnetic resonance (NMR). However, applications are limited due to the short lifetime of this non equilibrium spin state caused by relaxation processes. This issue can be addressed by storing hyperpolarization in slowly decaying singlet spin states which was so far mostly demonstrated for non-proton spin pairs, e.g. 13C-13C. Protons hyperpolarized by parahydrogen induced polarization (PHIP) in symmetrical molecules, are very well suited for this strategy because they naturally exhibit a long-lived singlet state. The conversion of the NMR silent singlet spin state to observable magnetization can be achieved by ma…
State of the art of CPMAS 13C-NMR spectroscopy applied to natural organic matter
2004
A number of different techniques are presently available for characterizing humified natural organic matter (NOM). Carbon-13 nuclear magnetic resonance spectroscopy (13C-NMR) in the solid state using cross-polarization (CP) and magic angle spinning (MAS) represents the most powerful experimental approach used to collect direct information on the structural and conformational characteristics of humic carbon backbones. Despite the problems due to the presence of paramagnetic impurities and the generally low organic matter concentration, cross-polarization magic angle spinning 13C-NMR spectroscopy (CPMAS 13C-NMR) is applied in soil chemistry and geochemistry mainly because of its relevance in …
Determination of the isotope shift in theD 1 line between197Au and195Au
1983
The isotope shift between197Au (stable) and195Au (T 1/2=183 d) was determined by resonance fluorescence and polarization spectroscopy in the 6s2 S 1/2 -6p 2 P 1/2, λ =267.6nm line. The result is δν195, 197=-2.9(2) GHz corresponding to a change of the mean-square charge radius by δ〈r 2〉195, 197=0.063(9) fm2. The sample was confined to a resonance cell heated to temperatures of up to 1500°C.
Enhancement of the laser-driven proton source at PHELIX
2020
High power laser science and engineering 8, e24 (2020). doi:10.1017/hpl.2020.23
Zero- to Ultralow-Field Nuclear Magnetic Resonance $J$-Spectroscopy with Commercial Atomic Magnetometers
2019
Zero- to ultralow-field nuclear magnetic resonance (ZULF NMR) is an alternative spectroscopic method to high-field NMR, in which samples are studied in the absence of a large magnetic field. Unfortunately, there is a large barrier to entry for many groups, because operating the optical magnetometers needed for signal detection requires some expertise in atomic physics and optics. Commercially available magnetometers offer a solution to this problem. Here we describe a simple ZULF NMR configuration employing commercial magnetometers, and demonstrate sufficient functionality to measure samples with nuclear spins prepolarized in a permanent magnet or initialized using parahydrogen. This opens …
Spatial and Spectral Distributions of the Hydrogen $\hbox{H}_{\alpha}$ Line in Dielectric-Barrier Discharges
2008
It is shown that the optical emission method, based on measured spatial and spectral distributions of the Halpha radiation, provides valuable information on physical conditions in the volume of dielectric-barrier discharges. In the case when the registration allows the determination of light polarization, the measured spectra may provide information about the distribution of the electric-field strength in a direction that is perpendicular to the surfaces limiting the discharge volume. Visualization of the experimental data of spatial distributions of the hydrogen Halpha line is presented.
Muon Anomaly from Lepton Vacuum Polarization and The Mellin--Barnes Representation
2008
We evaluate, analytically, a specific class of eighth--order and tenth--order QED contributions to the anomalous magnetic moment of the muon. They are generated by Feynman diagrams involving lowest order vacuum polarization insertions of leptons $l=e,\mu$, and $\tau$. The results are given in the form of analytic expansions in terms of the mass ratios $m_e/m_\mu$ and $m_\mu/m_\tau$. We compute as many terms as required by the error induced by the present experimental uncertainty on the lepton masses. We show how the Mellin--Barnes integral representation of Feynman parametric integrals allows for an easy analytic evaluation of as many terms as wanted in these expansions and how its underlyi…
Light baryons and their electromagnetic interactions in the covariant constituent quark model
2012
We extend the confined covariant constituent quark model that was previously developed by us for mesons to the baryon sector. In our numerical calculation we use the same values for the constituent quark masses and the infrared cutoff as have been previously used in the meson sector. In a first application we describe the static properties of the proton and neutron, and the $\Lambda$-hyperon (magnetic moments and charge radii) and the behavior of the nucleon form factors at low momentum transfers. We discuss in some detail the conservation of gauge invariance of the electromagnetic transition matrix elements in the presence of a nonlocal coupling of the baryons to the three constituent quar…
First measurement of helicity-dependent cross sections in π0η photoproduction from quasi-free nucleons
2018
The helicity-dependent cross sections for the photoproduction of $\pi^0\eta$ pairs have been measured for the first time. The experiment was performed at the tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball - TAPS calorimeter. The experiment used a polarized deuterated butanol target and a circularly polarized photon beam. This arrangement allowed the $\sigma_{1/2}$ (photon and target spin antiparallel) and $\sigma_{3/2}$ (parallel spins) components to be measured for quasi-free production of $\pi^0\eta$ pairs off protons and neutrons. The main finding is that the two helicity components contribute identically, within uncertainties, for both participant pr…
Performance and characterization of the FinEstBeAMS beamline at the MAX IV Laboratory
2021
European Regional Development Fund (grant No. TK-141 HiTechDevices 2014-2020.4.01.15-0011 to University of Tartu; grant No. MAX-TEENUS 2014-2020.4.01.20-0278 to University of Tartu; grant No. Eesti Kiirekanal SLOFY11156T/1 to University of Tartu); Estonian Research Council (grant No. PRG-629 to University of Tartu); Jane & Aatos Erkko Foundation (grant No. SOFUS); Business Finland (grant No. 1464/31/2019); Academy of Finland (grant No. 319042; grant No. 326461; grant No. 326406; grant No. 320165); University of Oulu; University of Turku; Tampere University; University of Tartu.