Hyperpolarization (HP) of nuclear spins is critical for ultrasensitive nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI). We demonstrate an approach for >1500-fold enhancement of key small-molecule metabolites: 1-(13)C-pyruvic acid, 1-(13)C-sodium lactate, and 1-(13)C-acetic acid. The (13)C solution NMR signal of pyruvic acid was enhanced 1600-fold at B = 1 T and 40 °C by pre-polarizing at 14 T and ∼2.3 K. This "brute-force" approach uses only field and temperature to generate HP. The noted 1 T observation field is appropriate for benchtop NMR and near the typical 1.5 T of MRI, whereas high-field observation scales enhancement as 1/B. Our brute-force process ejects the frozen, solid sample from the low-T, high-B polarizer, passing it through low field (B < 100 G) to facilitate "thermal mixing". That equilibrates (1)H and (13)C in hundreds of milliseconds, providing (13)C HP from (1)H Boltzmann polarization attained at high B/T. The ejected sample arrives at a room-temperature, permanent magnet array, where rapid dissolution with 40 °C water yields HP solute. Transfer to a 1 T NMR system yields (13)C signals with enhancements at 80% of ideal for noted polarizing conditions. High-resolution NMR of the same product at 9.4 T had consistent enhancement plus resolution of (13)C shifts and J-couplings for pyruvic acid and its hydrate. Comparable HP was achieved with frozen aqueous lactate, plus notable enhancement of acetic acid, demonstrating broader applicability for small-molecule NMR and metabolic MRI. Brute-force avoids co-solvated free-radicals and microwaves that are essential to competing methods. Here, unadulterated samples obviate concerns about downstream purity and also exhibit slow solid-state spin relaxation, favorable for transporting HP samples.

We have studied NMR spin echoes in 3 He liquid in a magnetic field #o = 8 T for temperatures T>4.5 mK. The data are analyzed in terms of the Leggett-Rice effect to obtain the transverse spindiffusion coefficient D± (T). For T<20 mK we find that D± is less than measured in earlier experiments at lower Bo. This phenomenon has been predicted for degenerate Fermi systems, due to the phase space created for quasiparticle scattering by spin polarization. The effect we have measured is more pronounced than suggested by scaling a dilute-gas theory result by a Fermi-liquid factor.PACS numbers: 67.65. +Z, 67.55.-s In degenerate Fermi liquids in which interparticle collisions dominate scattering ( 3 He and certain metallic systems), the transport coefficients diverge as the temperature T-* 0. This fundamental property is due to the restriction of scattering phase space to a shell of width kg about the Fermi surface. Recently, it was independently predicted by Meyerovich [1] and by Jeon and Mullin [2] that the divergence in the transverse spin-diffusion coefficient D± oc T~2 is removed by arbitrarily small spin polarization P of the system. Below a temperature T a which depends upon P, spin diffusion becomes anisotropic, with D±6 mK found no significant deviation from either the expected low-field behavior or the measured behavior [5] of D\\ at BQ=9.2 T. These earlier experiments used very dilute 3 He-4 He mixtures in which the 3 He quasiparticles form a weakly interacting gas. Thus, if polarization does cause D± < D\u this must occur at lower temperatures or higher fields.Reason to expect a lower value for T a has come from the kinetic-equation calculations of Jeon and Mullin [2]. For a dilute, weakly polarized Fermi gas with s-wave interactions, they obtained Ta^hyBjlTtkB.Unfortunately this suggests spin-diffusion anisotropy should be difficult to observe in available laboratory fields unless nuclear demagnetization were used to achieve much lower temperatures.In an attempt to observe the effect using conventional dilution refrigeration, we have studied spin diffusion in pure 3 He liquid at BQ^S T. Pure 3 He is a strongly in-teracting system, but for T<£T F it is successfully described by Fermi-liquid theory as a weakly interacting quasiparticle gas with strong mean-field effects. At zero pressure 7> = 1.8 K and mean-field effects enhance the effective magnetic field by a factor of (1 -FFg) _1 = 3.3, wh...

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Gadolinium gallium garnet, Gd3Ga5O12 (GGG) has an extraordinary low temperature phase diagram. Although the Curie–Weiss temperature of GGG is about −2 K, GGG shows no long-range order down to T∼0.4 K. At low temperatures GGG has a spin glass phase at low fields (⩽0.1 T) and a field-induced long-range order antiferromagnetic state at fields of between 0.7 and 1.3 T [P. Schiffer et al., Phys. Rev. Lett. 73, 2500 (1994), S. Hov, H. Bratsberg, and A. T. Skjeltorp, J. Magn. Magn. Mater. 15–18, 455 (1980); S. Hov, Ph.D. thesis, University of Oslo, 1979 (unpublished), A. P. Ramirez and R. N. Kleiman, J. Appl. Phys. 69, 5252 (1991)]. However, the nature of the ground state at intermediate fields is still unknown, and has been hypothesized to be a three-dimensional spin liquid. We have measured the thermal conductivity (κ) and heat capacity (C) of a high-quality single crystal of GGG in the low temperature regime in order to study the nature of this state. The field dependence of κ shows that phonons are the predominant heat carriers and are scattered by spin fluctuations. We observe indications in κ(H) and C(H) of both the field induced ordering and the spin glass phase at low temperatures (T⩽200 mK).

We consider the possibility of adding a stage to a dilution refrigerator to provide additional cooling by "filtering out" hot atoms. Three methods are considered: (1) effusion, where holes having diameters larger than a mean-free path allow atoms to pass through easily; (2) particle waveguidelike motion using very narrow channels that greatly restrict the quantum states of the atoms in a channel; (3) wall-limited diffusion through channels, in which the wall scattering is disordered so that local density equilibrium is established in a channel. We assume that channel dimensions are smaller than the mean-free path for atom-atom interactions. The particle waveguide and the wall-limited diffusion methods using channels on order of the de Broglie wavelength give cooling. Recent advances in nanofilters give this method some hope of being practical.