共查询到20条相似文献,搜索用时 15 毫秒
1.
Liquid 3He has been cooled by adiabatic demagnetization of copper nuclei to 1.6 mK, well into the region of the superfluid phases. NMR measurements on 3He in a coil partly filled with platinum powder give results different from those expected for bulk liquid. 相似文献
2.
NMR relaxation measurements of 3He in porous high silica glass within a temperature range of 0.5 to 4.2 K at various applied pressures up to 14.6 MPa are reported. The onset of solidification of 3He in the pores was observed at excess pressures ≈ 2.3?4.7 MPa above the bulk melting pressure between 1.3 and 2.1 K. The specific heat of 3He in the porous glass was measured to supplement the NMR measurements and the result confirmed the solidification. 相似文献
3.
G. V. Mamin Haruhiko Suzuki M. S. Tagirov D. A. Tayurskii A. N. Yudin 《JETP Letters》2004,79(12):641-645
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. 相似文献
4.
E. M. Alakshin E. I. Kondratyeva V. V. Kuzmin K. R. Safiullin A. A. Stanislavovas A. V. Savinkov A. V. Klochkov M. S. Tagirov 《JETP Letters》2018,107(2):111-114
The spin kinetics of liquid 3He in contact with a mixture of LaF3 (99.67%) and DyF3 (0.33%) micropowders at temperatures of 1.5–3 K has been studied by pulsed nuclear magnetic resonance (NMR). The DyF3 is a dipolar dielectric ferromagnet with the phase transition temperature Tc= 2.55 K, whereas the diamagnetic fluoride LaF3 is a diluting substance for the optimal observation conditions of 3Не NMR in powder pores. The magnetic phase transition in DyF3 is accompanied by a considerable change in the character of fluctuations of the magnetic moments of dysprosium ions, which affect the spin kinetics of 3Не in contact with the substrate. Significant changes in the relaxations rates of the longitudinal and transverse magnetizations of 3Не have been discovered in the region of magnetic ordering of the solid matrix. The technique of studying the static and fluctuating magnetic fields of a solid matrix at low temperatures using liquid 3He as a probe has been proposed. 相似文献
5.
3He spin relaxation time in the rotating frame (T1?) has been measured for 2% 3He in 4He solid samples of different molar volume at exchange plateau region (0.5 K). From the data, the characteristic frequency by which a 3He atom exchanges its position with a neighboring 4He atom is determined. 相似文献
6.
E. M. Alakshin R. R. Gazizulin A. V. Klochkov S. L. Korableva V. V. Kuzmin A. M. Sabitova T. R. Safin K. R. Safiullin M. S. Tagirov 《JETP Letters》2013,97(10):579-582
Spin kinetics of adsorbed and liquid 3He in contact with crystalline nanopowders of the Van Vleck paramagnet PrF3 at a temperature of 1.5 K has been studied by nuclear magnetic resonance. The correlation between the parameters of the nuclear magnetic relaxation of 3He and the sizes of the sample particles has been found. A qualitative model of the magnetic relaxation of 3He describing the experimental results has been proposed. 相似文献
7.
S. G. Kafanov A. Ya. Parshin I. A. Todoshchenko 《Journal of Experimental and Theoretical Physics》2000,91(5):991-999
An investigation is made of the absorption spectra of triplet metastable helium molecules in the a 3Σ u + state in liquid 4He and 3He at various pressures and in dense 3He gas. An analysis of the spectrum corresponding to the a 3Σ u + → c 3Σ g + transition confirms the conclusion that there is a microscopic bubble surrounding the molecule in liquid helium. A simple approximation is proposed for the wave function of the valence electron of the molecule and the parameters of the bubble are determined for various experimental conditions. The coefficient of molecular recombination in liquid 3He and 4He was determined experimentally at various pressures and in dense cold 3He gas. The results show good agreement with the theory of mutual recombination limited by molecular diffusion under conditions of strong van der Waals interaction. It is shown that in the condensed phases of helium the polarization of the molecules under the action of the magnetic field does not lead to suppression of their mutual recombination, and this is confirmed experimentally. 相似文献
8.
J. Schmiedeskamp W. Heil E. W. Otten R. K. Kremer A. Simon J. Zimmer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(3):427-438
In this first in a series of three papers on wall relaxation of spin
polarized, gaseous 3He we investigate both by theory and by experiment
surface-induced spin relaxation due to paramagnetic sites in the containing
glass. We present experimental and theoretical evidence that — contrary to
the traditional opinion — distant dipolar coupling to paramagnetic
impurities in the glass, in particular iron ions, cannot be the dominant
relaxation mechanism of 3He-spins, although iron dominates the bulk
static permeability. Instead dangling-bond type defects in the glass matrix
are found to interact much stronger via the isotropic Fermi contact
interaction. A model of paramagnetic site controlled 3He relaxation
including the Fermi contact interaction is presented. With reasonable
semi-empirical assumptions our model allows to describe satisfactorily the
measured relaxivities, both in the dissolution-dominated regime of fused
silica or borosilicate glasses of the Pyrex type as well as in the surface
dominated situation of aluminosilicate glasses which have only a low
permeability for He atoms. In a large sample of 1.1 litre cells, built from
various aluminosilicate glasses, an average relaxation time of 150 h is
reached in case contaminant ferromagnetic particles have been demagnetized
beforehand. From the maximum observed value of 250 h we derive after
subtraction of dipolar relaxation in the gas phase a paramagnetic surface
relaxivity of ρ<0.005 cm/h at room temperature. 相似文献
9.
H.T. Weaver 《Journal of Physics and Chemistry of Solids》1973,34(3):421-425
Transient nuclear magnetic resonance measurements of spin-lattice and spin-spin relaxation times have been carried out as a function of temperature and pressure on 3He adsorbed on two types of commercial zeolite. In addition, the number of atoms adsorbed on unit weights of zeolite was determined by spin counting. Mechanisms for spin-spin relaxation were provided by dipole interactions among helium spins and spin-lattice relaxation was probably due to atomic motion. 相似文献
10.
A. V. Klochkov V. V. Kuz’min K. R. Safiullin M. S. Tagirov D. A. Tayurskii N. Mulders 《JETP Letters》2008,88(12):823-827
The spin kinetics of 3He in an aerogel has been studied above the Fermi temperature. The magnetic relaxation times T 1 and T 2 of adsorbed, gaseous, and liquid 3He in a 95% silica aerogel at a temperature of 1.5 K have been determined as functions of frequency by means of pulse nuclear magnetic resonance. It has been found that the time T 1 is linear in frequency in all three cases, whereas T 2 is independent of frequency. To explain the observed behavior of the longitudinal relaxation rate, a theoretical model of relaxation in the adsorbed layer of 3He taking into account the filamentary structure of the aerogel is proposed. 相似文献
11.
12.
13.
Nuclear spin lattice relaxation time of 3He gas was measured as a function of oxygen between 0.25 and 15 at.% at room temperature and at 25 atm pressure using spin-echo. 相似文献
14.
At low temperature the positively charged muon (μ+) in solid3He is localized in a polaron which, unlike a chemically bound complex, is held together with polarizational attraction (van der Waals force). The dynamic effects in the muon relaxation are determined by the spin exchange of the3He atoms in the polaron. In crystals with large molar volumes (melting pressureP m<60 bar) the rate of magnetic field fluctuations at the muon site is at least one order of magnitude lower than in an unperturbed crystal. In an external electric field the μ+ produces an anisotropic local distortion which reduces the rate of the local3He spin exchange and leads to an increase of the muon spin relaxation rate. 相似文献
15.
Q. Ye G. Laskaris W. Chen H. Gao W. Zheng X. Zong T. Averett G. D. Cates W. A. Tobias 《The European Physical Journal A - Hadrons and Nuclei》2010,44(1):55-61
Following the first experiment on three-body photodisintegration of polarized 3He utilizing circularly polarized photons from High-Intensity Gamma Source (HIg \gamma S) at Duke Free Electron Laser Laboratory (DFELL), a new high-pressure polarized 3He target cell made of pyrex glass coated with a thin layer of sol-gel doped with aluminum nitrate nonahydrate has been built
in order to reduce the photon beam-induced background. The target is based on the technique of spin exchange optical pumping
of hybrid rubidium and potassium and the highest polarization achieved is ∼ 62% determined from both NMR-AFP and EPR polarimetries.
The phenomenological parameter that reflects the additional unknown spin relaxation processes, X , is estimated to be ∼ 0.10 and the performance of the target is in good agreement with theoretical predictions. We also
present beam test results from this new target cell and the comparison with the GE180 3He target cell used previously at HIg \gamma S. This is the first time that the sol-gel coating technique has been used in a polarized 3He target for nuclear-physics experiments. 相似文献
16.
E. M. Alakshin R. R. Gazizulin A. V. Klochkov V. V. Kuzmin N. Mulders M. S. Tagirov D. A. Tayurskii 《JETP Letters》2011,93(4):223-225
A new method for studying the processes of the establishment of the thermodynamic equilibrium in the adsorbed 3He layers in highly porous media has been proposed. Using this method, the thermalization of adsorbed 3He on silica aerogel at a temperature of 1.5 K has been studied. The process of the establishment of the thermodynamic equilibrium
has been controlled by measuring the pressure in an experimental cell, the amplitude of the NMR signal, and the nuclear spin-spin
and spin-lattice relaxation times of adsorbed 3He. It has been shown that the establishment of the thermodynamic equilibrium in the adsorbed 3He-aerogel system is characterized by a time of 26 min. 相似文献
17.
S. Karpuk F. Allmendinger M. Burghoff C. Gemmel M. Güldner W. Heil W. Kilian S. Knappe-Grüneberg Ch. Mrozik W. Müller E. W. Otten M. Repetto Z. Salhi U. Schmidt A. Schnabel F. Seifert Yu. Sobolev L. Trahms K. Tullney 《Physics of Particles and Nuclei》2013,44(6):904-908
Polarization of 3He gas by means of optical pumping is well known since the early 1960s with first applications in fundamental physics. Some thirty years later it was discovered, that one can use hyperpolarized 3He as contrast agent for magnetic resonance imaging of the lung. The wide interest in this new method made it necessary to find ways of polarizing 3He in large quantities with high polarization degrees. A high performance polarizing facility has been developed at the University of Mainz, designed for centralized production of hyperpolarized 3He gas. We present the Mainz concept as well as some examples of numerous applications of spin polarized 3He in fundamental research and medical applications. 相似文献
18.
《Physics letters. [Part B]》1988,202(2):179-184
The reaction 3He(d, p)4He has been investigated for ECM = 5.9−41.6 keV with the use of D projectiles and 3He atomic gas target nuclides as well as with 3He projectiles and D2 molecular gas target nuclides. These studies show for the first time the effects of electron screening on low-energy fusion cross sections, i.e. a nearly exponential enhancement of the cross sections compared to the case of bare nuclei. The enhancement is about a factor 2 smaller for the case d(3He, p)4He due to the molecular nature of the D2 target nuclides. 相似文献
19.
《Journal of Magnetic Resonance (1969)》1989,81(3):491-499
We measured the nuclear spin-lattice relaxation time T1, of several surface-bound nuclei, 1H, 19F, 11B, 13C, 29Si, and 2H, immersed in liquid 3He over the temperature range 0.01 K ⩽ T < 1 K. The Larmor frequencies of these nuclei in a 3.39 T field extended from 22 to 144 MHz. All T1 values were temperature-independent and ranged from a few seconds to several hours, depending on the particular nucleus and the surface geometry of the sample. The results indicate that the coupled relaxation of surface spins is a phenomenon occurring in all solids immersed in 3He and thus provides a general mechanism for obtaining high nuclear polarization in solids, that the relaxation is controlled by direct dipole-dipole interactions between the surface spins and 3He in the first surface layer, that the 3He motion dynamics do not change appreciably from one surface to another, and that measurements of T1 may thus be useful for determining the structure of surfaces. 相似文献
20.
《Physics letters. A》1986,117(9):477-480
Measurements of the transverse acoustic impedance of dilute solutions of 3He in superfluid 4He show that the fraction of 3He quasiparticles which are specularly reflected at a plane wall is temperature dependent between 0.1 and 1 K. Values of the 3He relaxation time are also obtained. 相似文献