A low-field, low-cost Halbach magnet array for open-access NMR

A working prototype of a novel low-cost Halbach-array-based NMR system is described. The new design provides open access to the sample relative to conventional NMR magnet designs and this facilitates the simultaneous use of multi-sensor techniques on the same sample, in which NMR/MRI can potentially be combined with other spectroscopies such as impedance spectroscopy, laser scattering and rheological experiments.     

Single-sided mobile NMR with a Halbach magnet

A single-sided mobile NMR apparatus with a small Halbach magnet was constructed for the first time. It is lightweight, compact and exhibits good sensitivity. The weight of the device is only 2 kg, and the NMR signal of the pencil eraser block can be detected in one shot using the device. This study describes the characteristics of this instrument, including the profile of static magnetic flux density, B0, the sensitivity in the depth direction and its effectiveness in one-dimensional profiling. Its usefulness in differentiating soft materials and evaluating the extent of damage of a material is demonstrated based on T2 relaxation data. The moisture absorbance also can be observed from the increase of the echo amplitude of the NMR spin echo signal.     

Cryostat attachment for IR spectrometers

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 50, No. 1, pp. 158–162, January, 1989.     

Cryostat for low temperature x-irradiation and electron paramagnetic resonance

A cryostat for x-irradiation of solid samples at liquid air temperature is described. The design of the sample mount in the cryostat enables quick transfer of the sample after x-irradiation into EPR cavity to facilitate EPR study without warming the sample.     

NMR line shape in one-dimensional magnet in the finite temperature region

The NMR line width is calculated for the one-dimensional ferro- and antiferro-magnets in the finite temperature region. The NMR line shape turns out to have a structure with double peaks which is quite different from the Lorentzian and the Gaussian type.     

A unilateral NMR magnet for sub-structure analysis in the built environment: the Surface GARField

A new, portable NMR magnet with a tailored magnetic field profile and a complementary radio frequency sensor have been designed and constructed for the purpose of probing in situ the sub-surface porosity of cement based materials in the built environment. The magnet is a one sided device akin to a large NMR-MOUSE with the additional design specification of planes of constant field strength /B0/ parallel to the surface. There is a strong gradient G in the field strength perpendicular to these planes. As with earlier GARField magnets, the ratio G//:B0/ is a system constant although the method of achieving this condition is substantially different. The new magnet as constructed is able to detect signals 50mm (1H NMR at 3.2 MHz) away from the surface of the magnet and can profile the surface layers of large samples to a depth of 35-40 mm by moving the magnet, and hence the resonant plane of the polarising field, relative to the sample surface. The matching radio frequency excitation/detector coil has been designed to complement the static magnetic field such that the polarising B0 and sensing B1 fields are, in principal, everywhere orthogonal. Preliminary spatially resolved measurements are presented of cement based materials, including two-dimensional T1-T2 relaxation correlation spectra.     

Cryostat RUPIK to SEM for depth profiling of object structure

The design features of the cryostat RUPIK to an SEM-100U microscope are described. This cryostat was tested on aqueous suspensions of ground coniferous wood and photographic films. A layer-by-layer SEM study at low temperatures made it possible to perform rapid structural analysis on different portions of these objects.     

NMR study on the quasi one-dimensional quantum spin magnet with ladder structure

The two-legged spin ladder Cu(CO₃)_0.5(ClO₄)(H₂O)_0.5(NH₃)_2.5 consists of a rung formed by two Cu(II)’s and of a spacing molecule CO\(_{3}^{2-}\) between each two rungs. The non-centrosymmetric shape of CO\(_{3}^{2-}\) molecule brings a slight bond alternation along the leg, and hence the system can be considered as an alternating spin chain, which is confirmed so far by the temperature dependence of magnetic susceptibility. In order to investigate its spin state at low temperatures, we have performed experiments of ¹H-NMR, magnetization and specific heat under wide range of magnetic field, and have found the critical diverging of longitudinal relaxation rate 1/T ₁, the spectral broadening and the lambda-type anomaly in specific heat at T _N? 3.4 K, indicating the existence of long range magnetic order. In paramagnetic state well above T _N, 1/T ₁ showed a power-law temperature dependence, suggesting the realization of Tomonaga Luttinger liquid state.     

Single-sided mobile NMR apparatus using the transverse flux of a single permanent magnet

This study presents a simple design for a mobile, single-sided nuclear magnetic resonance (NMR) apparatus which uses the magnetic flux parallel to the magnetization direction of a single, disc-shaped permanent magnet polarized in radial direction. The stray magnetic field above the magnet is approximately parallel to the magnetization direction of the magnet and is utilized as the B₀ magnetic field of the apparatus. The apparatus weighs 1.8 kg, has a compact structure and can be held in one's palm. The apparatus generates a B₀ field strength of about 0.279 T at the center of apparatus surface and can acquire a clear Hahn echo signal of a pencil eraser block lying on the RF coil in one shot. Moreover, a strong static magnetic field gradient exists in the direction perpendicular to the apparatus surface. The strength of the static magnetic field gradient near the center of the apparatus surface is about 10.2 T/m; one-dimensional imaging of thin objects and liquid self-diffusion coefficient measurements can be performed therein. The available spatial resolution of the one-dimensional imaging experiments using a 5×5 mm horizontal sample area is about 200 μm. Several nondestructive inspection applications of the apparatus, including distinguishing between polyethylene grains of different densities, characterizing epoxy putties of distinct set times and evaluating the fat content percentages of milk powders, are also demonstrated. Compared with many previously published designs, the proposed design bears a simple structure and generates a B₀ magnetic field parallel to the apparatus surface, simplifying apparatus construction and simultaneously rendering the selection of the radiofrequency coil relatively flexible.     

EAST托卡马克装置外冷屏的热负荷分析

外真空杜瓦冷屏 (简称外冷屏 )是 EAST超导托卡马克核聚变装置的重要部件之一 ,它在处于室温下的外真空杜瓦与运行在 4 .5 K温度下的超导线圈之间形成了一道隔热的屏障 ,以保证装置能够稳定高效的运行。文中运用有限元分析软件 ANSYS对外冷屏封头、中筒、底座的传热情况做了计算与分析 ,以得到在氦气入口处压强为 5 .2 bar,温度为 80 K的情况下 ,外冷屏低温面板的详细设计方案