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NMR 1 Temperature And It Effect To Different Environment (Term Paper Sample)




NMR T1 Temperature
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NMR T1 Temperature
The NMR (nuclear magnetic resonance) spectroscopy is a term that is used to describe relaxation of how signals change with time (Nelson, 2002). In NMR spectroscopy signals deteriorate with some time, and later it becomes weak and broader. The deterioration is used to describe the fact that NMR signal results from nuclear magnetization and they arise from the over-population of its excited state. The deterioration of an MNR signals can be classified into two distinct processes that are characterized by two separate processes with their own time constants. T1 is normally associated with different processes, but one of the major processes of T1 is its responsibility for the loss of signal intensity. T1 is the time constant that represents the all physical processes that are responsible for the relaxation of different components of the nuclear under the spin magnetization vector and usually denoted as M and is always parallel to the resulting external magnetic field denoted as B0 (Joseph & Eugene, 2003). In many cases of spectroscopy, T1 is applied to determine the recycle time of the relaxation and also the rate at which the NMR spectrum can be acquired. The values of T1 ranges from milliseconds to several seconds. Relaxation time T1 in NMR mostly depends on the rotational correlation time Tc. Tc is the correlation time for the molecules in solution and Tc mainly depends on the temperature of the molecules (Levitt, 2008). The relationship between T1 and temperature is also affected by the viscosity, Kb the Boltzmann constant, a is the radius of the molecule and the temperature is always given as absolute temperature T (Joseph & Eugene, 2003). Hence, spine-lattice relaxation is increased by stimulated emission and T1 becomes smallest, but it increases faster with increased temperature.
Hence, the spinal-lattice relaxation time (longitudinal) T1 = Decay constant of the z component, Mz = nuclear spin magnetization, and Mz, eq. is the thermal equilibrium value of the nuclear magnetization.
From the above figures, M z (t) = M z, eq (0) – [M z, eq – Mz (0)] e-t/T1.
If M which is at the Z plane is twisted to xy plane, the value of Mz approaches Zero (Mz (0)=0). Hence the first equation can be simplified as shown below.
Mz (t)= Mz, eq (1-e-t/T1)
From the above equation, assuming that magnetization recovers to a figure of around 63% with an equilibrium value of the one time constant T1, hence the inversion recovery experiment, T1 values can be obtained by inversion of the initial magnetization where Mz (0) = -Mz (eq). Hence the recovery can be calculated as
Mz (t) = Mz, eq (1-2e-t/T1)
The relationship between T1 and temperature shows a linear increase and increasing the concentration of the substance being tested greatly reduces T1, and it always weakens the dependence on temperature. The property of interest in T1 and T is usually the spin-lattice relaxation time, that produces the insight into the provided structure and the small-scale dynamics of the molecules and mainly applied in imaging, and improving the required contrast when the scan is weighted for T1. Hence, T1 is highly dependent on the temperature of the sample and its magnetic field. The field dependence is highly on this parameters, and is best studied and understood for a large number of different nuclei, while the temperature mostly dependence at very low fields even with the ordinary nuclei (Nelson, 2002).
Experimental Setup
The experiment was used to culminate and collection of data of images that are acquired from Earth’s field magnetic resonance imaging spectrometer (Joseph & Eugene, 2003). Teach Spin PS1-A pulse NMR spectrometer was used, and it consisted of a magnet that contained the magnetic field strength. A pulse programmer that was applied to create the required pulse stream that gates the synthesized radio frequency from the oscillator during the pulse burst. Coils that are capable of accepting the radio frequency pulse burst and impact a 12 Gauss rotating magnetic field were used. A receiver or a pickup coil was fixed to transverse the plane that was used to detect the recessing nuclear magnetization and produce signals from the RF amplitude detector on the oscilloscope. The oscilloscope was used read the free induction decay signal and also the resulting spin echo signal. Also, the experiment comprised of a mixer that contains multiples precessional signals from the sample magnetization with the master oscillator used to determine the Zero-beat output signal of the mixer on the oscilloscope (proper frequency of the oscillator) (Nelson, 2002).

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