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Magnetic Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
What is spin-lattice relaxation? It is the magnetic relaxation in which the excess potential energy associated with electron spins in a magnetic field is transferred to the lattice. (As used here, the term “lattice” does not refer to an ordered crystal but instead signifies degrees of freedom other than spin orientation, such as the translational motion of molecules in a liquid.) What is spin-lattice relaxation time T1? T1, also called the longitudinal relaxation time, characterizes the rate at which the longitudinal Mz component of the magnetization vector recovers. It is thus the time taken by the signal to recover around 63% [1 − (1/e)] of its starting value after being flipped into the transverse magnetic plane.
Multispectral Image Segmentation in Magnetic Resonance Imaging
Published in Edward R. Dougherty, Digital Image Processing Methods, 2020
Joseph R. Hornak, Lynn M. Fletcher
Spin-lattice relaxation is caused by time-varying magnetic fields at the Larmor frequency. These variations in the magnetic field at the Larmor frequency cause transitions between the spin states and hence change Mz. Time- varying fields are caused by the random rotational and translational motions of the magnetic moment possessing molecules in the sample. The frequency distribution of random motions in a solution varies with the temperature and viscosity of the solution. Therefore, T1 will not only vary as a function of temperature and the solvent but as a function of B0. In general, relaxation times tend get longer as fl0 and ν increase because there are fewer relaxation-causing frequency components present in the random motions of the molecules as ν increases.
Nuclear Magnetic Resonance
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
In NMR spectroscopy two primary relaxation processes occur. They are termed spin–lattice (longitudinal) relaxation (T1) and spin–spin (transverse) relaxation (T2). Spin–lattice relaxation is the time it takes an excited nucleus to release its energy to its lattice or surrounding environment. It is dependent on the magnetogyric ratio of the nucleus and the mobility of the lattice. Spin–spin relaxation describes the interaction between neighboring nuclei with identical precessional frequencies resulting in a decrease of the average lifetime of a nucleus in the excited state. This can result in line broadening. Both these relaxation processes need to be taken into account in the design and execution of NMR experiments [32]. A more detailed description of these processes is given next.
Probing interfacial dynamics of water in confined nanoporous systems by NMRD
Published in Molecular Physics, 2018
As for I(t), a sensitive way to probe temporal fluctuations of H(t) is to look at the spectral density of this magnetic noise, noted . This noise induces a nuclear magnetic relaxation process at the Larmor frequency ω or f = ω/2π. Using field-cycling NMR spectroscopy, the related spin–lattice relaxation rate R1(ω) can be measured over a large range of frequencies, mainly from few kHz to several tens of MHz. This frequency range allows probing correlation times ranging from 1 ns to tenths of µs. In the following, we will use a normalisation of the spectral density such as: Without considering the contribution of the confined fluid in the bulk (which is essentially constant at the low magnetic field) but considering the intermittence process only, the spin–lattice relaxation rate is written after the former normalisation as [16]:
Field-cycling NMR relaxometry: the benefit of constructing master curves
Published in Molecular Physics, 2018
M. Flämig, M. Hofmann, E. A. Rössler
Ever since the pioneering work of Bloembergen, Purcell, and Pound (BPP) [1], measuring the frequency (field) dependence of the spin–lattice relaxation rate R1(ω) = 1/T1(ω) has been an important tool for studying the molecular dynamics in condensed matter as it allows to directly probe the underlying spectral density. Early studies monitored the relaxation mainly as a function of temperature, yet, only for a few frequencies due to the low sensitivity of NMR at low fields. This limitation is overcome by the field-cycling (FC) technique, i.e. the relaxation performed at different fields is decoupled from polarisation and detection by rapidly switching (‘cycling’) the external magnetic field. First FC relaxation studies were restricted to a few groups applying a home-built relaxometer [2]. This changed with the availability of a commercial electronic FC relaxometer since 1997 [3]. It is now routinely possible to measure R1(ω) in a frequency range of 10 kHz < ω/2π < 30 MHz (1H) [4–7]. Taking recourse to home-built instruments and compensating for earth and stray field, frequencies down to 100 Hz are accessible [8–10]. Very recently, experiments even down to 3 Hz were reported [11], and further instrumental developments are ongoing [12–17].
Predicting quadrupole relaxation enhancement peaks in proton R1-NMRD profiles in solid Bi-aryl compounds from NQR parameters
Published in Molecular Physics, 2018
Christian Gösweiner, Danuta Kruk, Evrim Umut, Elzbieta Masiewicz, Markus Bödenler, Hermann Scharfetter
An application of nuclear magnetic resonance (NMR), forming a field of research by its own, is the measurement of spin-lattice relaxation rates of nuclear spins. Experiments can be performed on a great variety of materials from condensed matter to liquids. As one is typically interested in molecular motions, such measurements are done temperature and/or field dependent by means of NMR field cycling (FC) relaxometry [1]. This method allows to study () of protons on a broad band Larmor frequency scale which is achieved by stepping the external magnetic field value (evolution field) applied to the sample at different cycles during a dispersion measurement. The experimental procedure uses an elaborate way of cycling the magnetic field in a sequence for enabling polarisation, evolution and detection of a nuclear spin ensemble. The evolution field can typically be varied to create proton Larmor frequencies from as low as 10 kHz to about 40 MHz. The experiments presented later in this article, however, are conducted between 20 and 128 MHz by the use of an additional superconducting 3 T magnet [2]. An early detailed description of the method can be found in the work of F. Noack [3], a more recent review is given in reference [1]. FC-NMR relaxometry nowadays is a standard analysis method and is applied to a wide range of research fields as, e.g. ionic crystals [4], liquid crystals [5], lipids [6], polymer dynamics [7], porous media [8] or, as formulated quite generally in another review [9], to molecular dynamics in complex media. The resulting measurements of the frequency dependence of are often referred to as nuclear magnetic relaxation dispersion (NMRD) profile. A method for gaining insight into molecular dynamics from analysing NMRD profiles is, e.g. the Redfield relaxation theory [10].