Detection of tobacco smoke deposition by hyperpolarized krypton-83 MRI

Despite the importance of the tobacco smoke particulate matter in the lungs to the etiology of pulmonary disease in cigarette smokers, little is currently known about the spatial distribution of particle deposition or the persistence of the resulting deposits in humans, and no satisfactory technique currently exists to directly observe tobacco smoke condensate in airways. In this proof-of-principle work, hyperpolarized (hp) 83Kr MRI and NMR spectroscopy are introduced as probes for tobacco smoke deposition in porous media. A reduction in the hp-83Kr longitudinal (T1) relaxation of up to 95% under near-ambient humidity, pressure and temperature conditions was observed when the krypton gas was brought into contact with surfaces that had been exposed to cigarette smoke. This smoke-induced acceleration of the 83Kr self-relaxation was observed for model glass surfaces that, in some experiments, were coated with bovine lung surfactant extract. However, a similar effect was not observed with hp-(129)Xe indicating that the 83Kr sensitivity to smoke deposition was not caused by paramagnetic species but rather by quadrupolar relaxation due to high adsorption affinity for the smoke deposits. The 83Kr T1 differences between smoke-treated and untreated surfaces were sufficient to produce a strong contrast in variable flip angle FLASH hp-83Kr MRI, suggesting that hp-83Kr may be a promising contrast agent for in vivo pulmonary MRI.     

Proton NMR relaxation as a probe for setting cement pastes

We report a 20-MHz proton nuclear magnetic resonance T1 relaxation study of cement paste hydration in the early stages of setting, using different centimeter-sized samples of cements of various origins and different water-to-cement ratios. In every sample, during the first few minutes of hydration, it is found that inverse Laplace processing of inversion-recovery measurements systematically exhibits at least two T1 values: a long one, around 100 ms, whose value correlates well with water content and which may be attributed to bulk water surrounding cement grains; and a short one, around 2 ms, which is quite insensitive to water-to-cement ratio and which may be attributed to water embedded in floculated cement grains before setting occurs. The time evolution of the longest T1 value for several hours is also shown to exhibit a characteristic five-stage behavior that is well correlated with known stages of the hydration process: initial reaction, induction period, acceleration period, deceleration period and slow hydration reaction. These results are compared with calorimetric measurements and electrical conductivity literature.     

Transverse NMR relaxation as a probe of mesoscopic structure

Transverse NMR relaxation in a macroscopic sample is shown to be extremely sensitive to the structure of mesoscopic magnetic susceptibility variations. Such a sensitivity is proposed as a novel kind of contrast in the NMR measurements. For suspensions of arbitrary-shaped paramagnetic objects, the transverse relaxation is found in the case of a small dephasing effect of an individual object. Strong relaxation rate dependence on the objects' shape agrees with experiments on whole blood. Demonstrated structure sensitivity is a generic effect that arises in NMR relaxation in porous media, biological systems, as well as in kinetics of diffusion limited reactions.     

Pulmonary MRI contrast using Surface Quadrupolar Relaxation (SQUARE) of hyperpolarized Kr

Hyperpolarized ⁸³Kr has previously been demonstrated to enable MRI contrast that is sensitive to the chemical composition of the surface in a porous model system. Methodological advances have lead to a substantial increase in the ⁸³Kr hyperpolarization and the resulting signal intensity. Using the improved methodology for spin exchange optical pumping of isotopically enriched ⁸³Kr, internal anatomical details of ex vivo rodent lung were resolved with hyperpolarized ⁸³Kr MRI after krypton inhalation. Different ⁸³Kr relaxation times were found between the main bronchi and the parenchymal regions in ex vivo rat lungs. The T₁ weighted hyperpolarized ⁸³Kr MRI provided a first demonstration of surface quadrupolar relaxation (SQUARE) pulmonary MRI contrast.     

Muon spin relaxation as a probe of molecular dynamics of organometallic compounds

LF‐Muon Spin Relaxation data are reported for the organometallic compounds Pb(C₆H₅)₄, (C₆H₆)Cr(CO)₃ and (C₅H₅)₂Ru. In each case the change in relaxation rate with temperature shows a peak analogous to the T_1 minimum in NMR. The activation parameters were calculated, and the mechanism of muon spin relaxation in the case of (C₆H₆)Cr(CO)₃ is shown to be the reorientation motion of the benzene ring. This revised version was published online in August 2006 with corrections to the Cover Date.     

83mKr, a potentially powerful PAC probe

In the decay of ⁸³Rb to ^83mKr and the subsequent decay to the ⁸³Kr ground state a 553–9.4 keV γ-γ and a 17.85–9.4 keV e^?-γ cascade are populated. The intermediate 9.4 keV 7/2^?+? state with a half-life of 154 ns is a perfect candidate for the application of the perturbed angular correlation (PAC) technique. Thus, it is possible to investigate the lattice environment of the implanted probes via the electric quadrupole interaction of the 9.4 keV 7/2^?+? state with the electric field gradient produced by the host lattices. Details of the production of this new PAC probe and planned measurements will be discussed.     

On argon beams as tools to probe surfaces

We present experimental data and a theoretical analysis for the scattering of an argon beam from the (001) surface of LiF. The scattering pattern of the Ar beam was investigated for incident energies between 0.089 and 0.350 eV and for a variety of polar and azimuthal incidence angles. We find a bilobular scattering pattern for small incidence angles and along the direction of maximum corrugation on the surface, and a broad peak centered around the specular direction for higher incidence angles. An interaction potential based on the effective medium theory has been evaluated. The corrugation of this potential across the surface is in fair agreement with the data interpreted using the classical rainbow angles. Such corrugation is smaller than the one determined by He scattering, in agreement with previous Ar/metal surface investigations.     

NMR as a probe of the relaxation of the magnetization in magnetic molecules

We investigate the time autocorrelation of the molecular magnetization M(t) for three classes of magnetic molecules (antiferromagnetic rings, grids, and nanomagnets), in contact with the phonon heat bath. For all three classes, we find that the exponential decay of the fluctuations of M(t) is characterized by a single characteristic time tau(T,B) for not too high temperature T and field B. This is reflected in a nearly single-Lorentzian shape of the spectral density of the fluctuations. We show that such fluctuations are effectively probed by NMR, and that our theory explains the recent phenomenological observation by Baek et al. [Phys. Rev. B 70, 134434 (2004)] that the Larmor-frequency dependence of 1/T(1) data in a large number of AFM rings fits to a single-Lorentzian form.     

Zero field spin relaxation studies as a probe of positive muon diffusion mechanisms

A theory of spin relaxation in zero external field is developed for a nonstationary distribution of diffusing particles. Application to μSR experiments in Nb and Bi is made to distinguish between models of muon diffusion in the presence of traps.     

Metal Auger intensity ratios as a probe for change-transfer effects in aluminum-covered transition metal surfaces

Marked changes in the LVV/LMV and LVV/LMM Auger intensity ratios of Co, Ni and Cu are observed on depositing Al on their surfaces. These changes, ascribed to charge-transfer or hybridization effects, are accompanied by changes in the intensity of the satellites next to the core levels of the transition metals.     

Atom scattering as a probe of the surface electron-phonon interaction at conducting surfaces

An atomic projectile colliding with a surface at kinetic energies in the thermal or hyperthermal range interacts with and is reflected by the electronic density well in front of the first layer of target atoms, and it is generally accepted that the repulsive interaction potential is proportional to the density of electrons extending outside the surface. This review develops a complete treatment of the elastic and inelastic scattering of atoms from a conducting surface in which the interaction with the electron density and its vibrations is treated using electron-phonon coupling theory. Starting from the basic principles of formal scattering theory, the elastic and inelastic scattering intensities are developed in a manner that identifies the small overlap region in the surface electron density where the projectile atom is repelled. The effective vibrational displacements of the electron gas, which lead to energy transfer through excitation of phonons, are directly related to the vibrational displacements of the atomic cores in the target crystal via electron-phonon coupling. The effective Debye-Waller factor for atom-surface scattering is developed and related to the mean square displacements of the atomic cores. The complex dependence of the Debye-Waller factor on momentum and energy of the projectile, including the effects of the attractive adsorption well in the interaction potential, are clearly defined. Applying the standard approximations of electron-phonon coupling theory for metals to the distorted wave Born approximation leads to expressions which relate the elastic and inelastic scattering intensities, as well as the Debye-Waller factor, to the well known electron-phonon coupling constant λ. This treatment reproduces the previously obtained result that the intensities for single phonon inelastic peaks in the scattered spectra are proportional to the mode specific mass correction components λ_Q,ν defined by the relationship λ = 〈λ_Q,ν〉. The intensities of elastic diffraction peaks are shown to be a weighted sum over the λ_Q,ν, and the Debye-Waller factor can also be expressed in terms of a similar weighted summation. In the simplest case the Debye-Waller exponent is shown to be proportional to λ and for simple metals, metal overlayers, and other kinds of conducting surfaces values of λ are extracted from available experimental data. This dependence of the elastic and inelastic scattering, and that of the Debye-Waller factor, on the electron-phonon coupling constant λ shows that measurements of elastic and inelastic spectra of atomic scattering are capable of revealing detailed information about the electron-phonon coupling mechanism in the surface electron density.     

Quadrupolar glass as a model for charge carrier transport in nonpolar organic materials

Monte Carlo simulation of the charge carrier transport in disordered nonpolar organic materials has been carried out. As a suitable model we considered the model of quadrupolar glass. A general formula for the temperature and field dependence of the mobility was suggested. A comparison with experimental data has been carried out.     

Auger electron spectroscopy - a local probe for solid surfaces

The Auger electron transition in solids is discussed under the aspect of a local excitation due to the strongly localized primary hole in an inner atomic core level. In first approximation the solid is represented by a cluster model, consisting of the excited atom and its neighbors. Using this simple model it is possible to describe the Auger electron energies, intensities and line shapes of transitions in solids in a satisfactory way. Only for the angular dependent Auger emission, characteristic long-range crystalline order has to be taken into account. It is the aim of this introductory review to point out that Auger spectra bear more information about the solid surface and particularly on its chemical bonds as has yet been exploited by surface spectroscopists.     

Ion beam as a probe to study the behavior of hydrogen on silicon surfaces

Hydrogen adsorption and its behavior on Si surfaces is studied by ion beam techniques in the energy range of MeV–keV. Elastic recoil detection analysis employing MeV ion beams is one of the most reliable experimental techniques for direct determination of absolute hydrogen coverages on Si surfaces. Results of its application to Si(1 0 0) and Si(1 1 1) clean surfaces are described. Important new results of the role of adsorbed hydrogen on the growth process or structures of metallic thin films on Si(1 1 1) surfaces also are described. Characterization of the growth process or structure of the thin films, as well as the characterization of hydrogen, is performed by ion beam techniques.     

Slow relaxation of the spin doublet decamethylferrocenium cation as a probe for spin on organo-polycyanides,new organoferromagnets

The contributions of Mössbauer spectroscopy and susceptibility studies to the discovery of a variety of new and some cases unprecedented magnetic behavior in polymeric charge transfer salts are highlighted. The materials are based on electron transfer from decamethylferrocene to polycyanide electron acceptors.     

Polyaniline films with nanostructure used as neural probe coating surfaces

Polyaniline (PANi) films with high conductivity and nanostructure were prepared by a modified dipping method using four acids on a polytetrafluoroethylene (PTFE) substrate. The “doping-dedoping-redoping” process was carried out to investigate whether the electrical and surface properties of PANi coating could be changed. We found that the conductivity decreased with prolonged immersing time in both water and DMEM, until the PANi films were almost non-conductive. The as-prepared PANi films were hydrophilic, and the immersing treatment with DMEM made them hydrophobic. Moreover, they recovered their hydrophilicity following the redoping treatment. The morphologies of the PANi films became heterogeneous after the immersing-redoping treatment. These results provide a good reference for the use of conducting polymers as a neural probe coating.