The Frequency Shifts of the Nuclear Magnetic Momenta Larmor Precession in the Mixture of Two Noble Gases

The dynamics of nuclear magnetization in the mixture of two noble gases with different gyromagnetic ratios of the nuclei is studied theoretically. The nuclear magnetization is induced by the radiofrequency electromagnetic radiation, which causes the nuclear magnetic resonance in both types of noble gases in the mixture. Frequency shifts of the nuclear magnetic resonance appeared due to an interaction between different types of the noble gases is analytically predicted. The specifics of these shifts are such that they cannot be compensated by means of the external magnetic field. The nature of the magnetic field distortion in the cell caused by the nuclear magnetization is also discussed.     

Nuclear magnetic resonance of laser-polarized noble gases in molecules,materials, and organisms

The sensitivity of conventional nuclear magnetic resonance (NMR) techniques is fundamentally limited by the ordinarily low spin polarization achievable in even the strongest NMR magnets. However, by transferring angular momentum from laser light to electronic and nuclear spins, optical pumping methods can increase the nuclear spin polarization of noble gases by several orders of magnitude, thereby greatly enhancing their NMR sensitivity. This review describes the principles and magnetic resonance applications of laser-polarized noble gases. The enormous sensitivity enhancement afforded by optical pumping can be exploited to permit a variety of novel NMR experiments across numerous disciplines. Many such experiments are reviewed, including the void-space imaging of organisms and materials, NMR and MRI of living tissues, probing structure and dynamics of molecules in solution and on surfaces, NMR sensitivity enhancement via polarization transfer, and low-field NMR and MRI.     

Nuclear spin-lattice relaxation of dilute Mn in Cu,Ag, and Au

We have developed a new method of determining nuclear spinlattice relaxation times of dilute impurity nuclei in non-magnetic host metals. Direct measurement of these extremely rapid relaxation times has hitherto been difficult. The present method is based on fast pulsed heating of a sample containing oriented radioactive nuclei and is applicable to a wide range of impurity-host combinations and over a large range of applied magnetic fields. Results are presented for extremely dilute Mn in noble metal hosts.     

Nuclear spin-lattice relaxation in finely dispersed carbonizate powders

Finely dispersed carbonizate powders were studied with the aim of revealing their suitability for producing hyperpolarized noble gases. In the temperature and frequency dependences obtained over a wide range of temperatures and magnetic fields for the spin-lattice relaxation times of the magnetic moments of ³He, ¹H, and ¹³C nuclei, anomalous features caused by the suppression of the exchange between surface paramagnetic centers in a magnetic field were observed. It is shown that the interaction with magnetic moments of the ¹H nuclei situated near the paramagnetic centers is the main polarization-leakage channel for the noble-gas nuclear spins.     

Novel MRI applications of laser-polarized noble gases

Gas-phase nuclear magnetic resonance (NMR) has great potential as a probe for a variety of interesting physical and biomedical problems that are not amenable to study by water or similar liquid. However, NMR of gases was largely neglected due to the low signal obtained from the thermally polarized gases with very low sample density. The advent of optical pumping techniques for enhancing the polarization of the noble gases³He and¹²⁹Xe has bought new life to this field, especially in medical imaging where³He lung inhalation imaging is approaching a clinical application. However, there are numerous applications in materials science that also benefit from the use of these gases. We review primarily nonmedical applications of laser-polarized noble gases for both NMR imaging and spectroscopy and highlight progress with examples from our laboratory including high-resolution imaging at millitesla applied field strength and velocity imaging of convective flow. Porous media microstucture has been probed with both thermal and laser-polarized xenon, as xenon is an ideal probe due to low surface interaction with the grains of the porous media.     

Quantum well and quantum wire states at metal surfaces

Novel effects in magnetic multilayer structures, such as oscillatory magnetic coupling and "giant" magnetoresistance, have created new materials that allow for an order of magnitude higher sensitivity in the detection of magnetically-recorded data. Determination of their electronic and magnetic structures with angle-resolved photoemission and inverse photoemission reveals quantized states in the noble metal spacer layers which are connected with oscillatory magnetic coupling and have implications on magnetoresistance. These states can be understood by a simple interferometer model, including the spin-dependent interface reflectivity that polarizes them and transmits the magnetic coupling through the noble metal spacer.Current efforts are discussed, which aim towards fabricating quantum wires and lateral superlattices on metals by decorating steps at vicinal surfaces. STM work on the growth mode of such structures is presented, which uses spectroscopic contrast to distinguish different metals. Specific electronic states at decorated step edges are found with inverse photoemission.     

超极化气体肺部磁共振成像

磁共振成像(MRI)技术具有非侵入、无放射性的特点,在临床疾病诊断中具有独特的优势,但是肺部空腔的特殊结构使传统质子MRI无法对其直接成像.自旋交换光抽运(SEOP)方法可以使惰性气体原子的极化度增强4个量级以上,从而使肺部的气体MRI成为可能.该文介绍了超极化惰性气体肺部MRI的最新研究进展,包括超极化气体磁共振相关参数的测量方法、肺部通气结构成像、肺部气体交换功能成像,同时比较了常用于肺部MRI气体的优点和缺点.     

Nuclear Spin Maser Oscillation of 129Xe by Means of Optical-Detection Feedback

We have developed the nuclear spin maser oscillating at a low frequency of 34 Hz with highly polarized nuclear spins of the noble gas element ¹²⁹Xe. The system is advantageous for detecting a small frequency shift of the nuclear spin precession. We are thus planning to apply this system to the search for an atomic electric dipole moment of ¹²⁹Xe. We here report the development of the system and its performance.     

Spectroscopic issues in optical polarization of 3He gas for Magnetic Resonance Imaging of human lungs

The Magnetic Resonance Imaging (MRI) of human lungs for diagnostic purposes became possible by using nuclear spin hyperpolarized noble gases, such as ³He. One of the methods to polarize ³He is the Metastability Exchange Optical Pumping (MEOP), which up to now has been performed at low pressure of about 1 mbar and in low magnetic field below 0.1 T (standard conditions). The equilibrium nuclear polarization can reach up to 80%, but it is dramatically reduced during the subsequent gas compression to the atmospheric pressure that is necessary for the lungs examination. Further polarization losses occur during the transportation of the gas to the hospital scanner. It was shown recently that up to 50% polarization can be obtained at elevated pressure exceeding 20 mbar, by using magnetic field higher than 0.1 T (nonstandard conditions). Therefore, following the construction of the low-field MEOP polarizer located in the lab, a dedicated portable unit was developed, which uses the magnetic field of the 1.5 T MR medical scanner and works in the continuous-flow regime. The first in Poland MRI images of human lungs in vivo were obtained on the upgraded to ³He resonance frequency Siemens Sonata medical scanner. An evident improvement in the image quality was achieved when using the new technique. The paper shows how spectroscopic measurements of ³He carried out in various experimental conditions led both to useful practical results and to significant progress in understanding fundamental processes taking place during MEOP.     

Nuclear and atomic models

A theorem concerning fermion interaction is postulated and applied to the problems of atomic (electronic) and nuclear physics. Model building basedsolely upon the postulate thatadjacent like fermions must be singlet paired accounts for the closed shells ofboth nuclear and atomic structure. The implied antiferromagnetic FCC lattice of protons and neutrons in alternating layers has been found previously to be the lowest-energy solid configuration of nuclear matter (N=P) (Canuto and Chitre, 1974). The buildup of the FCC lattice from a central tetrahedron reproduces all of the shells and subshells of the isotropic harmonic oscillator, which of course is the basis for the shell model. In atomic structure, the singlet pairing of adjacent electrons implies closed-shell structures uniquely at the six noble gases and the three noble metals, Ni, Pd, and Pt. The basis for the postulate concerning fermions is found in terms of classical electrodynamics; it is a microscopic corollary of Biot-Savart's law that parallel currents attract whereas antiparallel currents repel.     

原位核磁共振技术研究共催化剂类型以及光照波长对甲醇光催化重整产物的影响

本文采用原位核磁共振的方法研究了在真实固-液环境中共催化剂类型以及光照波长对甲醇光催化重整产物及光解水产氢产率的影响.结果发现,不同贵金属担载的锐钛矿型二氧化钛催化剂对甲醇光催化重整产物的产量和产率有着不同程度的影响,但是对其动力学特征影响不大.光照波长对甲醇光催化重整产物的产量也影响较大.通过对比甲醇氧化产率与产氢产率,发现共催化剂的种类对光催化反应速率及氧化还原能力起重要作用,且共催化剂的种类会影响体系氧化和还原能力之间的协同性.     

Relaxation of hyperpolarized 129Xe in a deflating polymer bag

In magnetic resonance imaging with hyperpolarized (HP) noble gases, data is often acquired during prolonged gas delivery from a storage reservoir. However, little is known about the extent to which relaxation within the reservoir will limit the useful acquisition time. For quantitative characterization, 129Xe relaxation was studied in a bag made of polyvinyl fluoride (Tedlar). Particular emphasis was on wall relaxation, as this mechanism is expected to dominate. The HP 129Xe magnetization dynamics in the deflating bag were accurately described by a model assuming dissolution of Xe in the polymer matrix and dipolar relaxation with neighboring nuclear spins. In particular, the wall relaxation rate changed linearly with the surface-to-volume ratio and exhibited a relaxivity of κ=0.392±0.008 cm/h, which is in reasonable agreement with κ=0.331±0.051 cm/h measured in a static Tedlar bag. Estimates for the bulk gas-phase 129Xe relaxation yielded T1bulk=2.55±0.22 h, which is dominated by intrinsic Xe-Xe relaxation, with small additional contributions from magnetic field inhomogeneities and oxygen-induced relaxation. Calculations based on these findings indicate that relaxation may limit HP 129Xe experiments when slow gas delivery rates are employed as, for example, in mouse imaging or vascular infusion experiments.     

The magnetic behavior of Co atoms on the surface and in the interior of the noble metals Au,Ag and Cu

The magnetism of Co atoms in the interior and on the surface of the noble metals has been studied by means of the anomalous Hall effect. On the surface of all three noble metals Co possesses a magnetic moment even at lowest studied coverages of 0.02 atomic layers. Ferromagnetic ordering appears at Co thicknesses of about one atomic layer. Co as a bulk impurity is non-magnetic in Cu whereas it is magnetic in Ag.     

Estimation of the Influence of the Magnetic Component on the Transition Rate in a Linearly Polarized Laser Field

We theoretically improved the relativistic ADK formula for a linearly polarized laser field. We have taken into account the influence of the magnetic component of laser field on the transition rate, in near relativistic field intensity. It was shown that the magnetic component results in a decrease of the transition rate in comparison to the results obtained by the original relativistic expression. We gave considered noble and alkali atoms. The obtained results show that this influence is larger (more significant) for alkali atoms.     

Magnetic stimulation of an impurity by a vacancy

The Green functions derived in the preceding letter are used to show how a vacancy in a noble metal could stimulate a non-magnetic transition metal atom to become magnetic.     

Hyperpolarized (131)Xe NMR spectroscopy

Hyperpolarized (hp) (131)Xe with up to 2.2% spin polarization (i.e., 5000-fold signal enhancement at 9.4 T) was obtained after separation from the rubidium vapor of the spin-exchange optical pumping (SEOP) process. The SEOP was applied for several minutes in a stopped-flow mode, and the fast, quadrupolar-driven T(1) relaxation of this spin I = 3/2 noble gas isotope required a rapid subsequent rubidium removal and swift transfer into the high magnetic field region for NMR detection. Because of the xenon density dependent (131)Xe quadrupolar relaxation in the gas phase, the SEOP polarization build-up exhibits an even more pronounced dependence on xenon partial pressure than that observed in (129)Xe SEOP. (131)Xe is the only stable noble gas isotope with a positive gyromagnetic ratio and shows therefore a different relative phase between hp signal and thermal signal compared to all other noble gases. The gas phase (131)Xe NMR spectrum displays a surface and magnetic field dependent quadrupolar splitting that was found to have additional gas pressure and gas composition dependence. The splitting was reduced by the presence of water vapor that presumably influences xenon-surface interactions. The hp (131)Xe spectrum shows differential line broadening, suggesting the presence of strong adsorption sites. Beyond hp (131)Xe NMR spectroscopy studies, a general equation for the high temperature, thermal spin polarization, P, for spin I ≥ 1/2 nuclei is presented.     

Temperature dependence of21Ne,83Kr,and131Xe quadrupole relaxation and of xenon diffusion in polyatomic solvents

The main aim of the present work is to contribute, by an extension of the experimental data base, to the understanding of quadrupole relaxation of nuclei of noble gases dissolved in molecular liquids. We have performed temperature dependent spin-lattice relaxation rate measurements of²¹Ne,⁸³Kr, and¹³¹Xe in various non-aqueous solvents (e.g. in methanol, ethanol, n-butanol, acetone, acetonitrile, benzene, carbon tetrachloride, N,N-dimethylformamide, dodecane, tetradecane, p-xylene, and hexafluorobenzene). In nine liquids we also measured translational diffusion coefficients of dissolved xenon as a function of temperature by the NMR spin-echo technique, obtaining partly the very first diffusion data for a number of systems. The comparison of the remarkable low activation energies for the noble gas nuclear quadrupole relaxation with that of the noble gas diffusion reveals that both seem to be closely connected. There are strong hints that the nuclear relaxation process follows an empirical “Dη ^γ =A correlation” found previously by Evans and co-workers for the tracer diffusion of noble gases in polyatomic liquids. For almost all solvents γ decreases from¹³¹Xe to²¹Ne parallel with a decrease of the corresponding activation energy for the quadrupolar relaxation. Possible physical reasons for this behavior are briefly discussed. Essential qualitative results in this paper were found to agree with two MD computer simulations for¹³¹Xe relaxation in benzene and methanol. Further MD simulations are proposed which are obviously required for the deeper understanding of the experimental results found in the present paper.     

Theory of the magnetic susceptibility of liquid metal alloys: Noble metal-tin systems

The theory of the effect of the ions on the magnetic susceptibility of conduction electrons has been extended to liquid metal alloys. Detailed calculations have been performed for the noble metal-tin systems. It is concluded that the non linear variation of the susceptibility with concentration of these alloys can be explained in terms of conventional pseudopotential theory.     

Scattering of surface plasmon polaritons by a nanoparticle with the inclusion of the magnetic dipole contribution

Using the method of the tensor Green’s function of the wave equation, the differential and total cross sections for the scattering of surface optical electromagnetic waves (surface plasmon polaritons) by a spherical nanoparticle into surface plasmon polaritons and light have been obtained with the inclusion of the magnetic dipole contribution. Using the example of noble metal systems, it has been shown that the magnetic dipole contribution may significantly affect the angular dependence of the differential cross sections and increase their anisotropy as the plasmon wavelength increases.     

Effect of double nuclear scattering on nuclear-magnetic interference in experiment with small-angle diffraction of polarized neutrons

An experiment on small-angle polarized-neutron diffraction by a two-dimensional spatially ordered array of nickel nanowires embedded in a porous anodic alumina matrix is discussed. The contributions of nonmagnetic (nuclear) structures and nuclear magnetic interference indicating the correlation between magnetic and nuclear structures are discussed. Magnetic scattering is two orders of magnitude smaller than nuclear scattering and, hence, turns out to be weakly distinguishable. The ordered magnetic composite nanostructure of a sample leads to strong interaction between the neutron wave and the structure itself, which, in turn, implies a twofold (miltiple scattering) nuclear scattering process. Nuclear magnetic interference scattering must be analyzed allowing for twofold scattering conditions, which substantially distorts the intensity distribution of the interference contribution of first-order diffraction peaks.