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PARAMETRICALLY NUCLEAR SPECTROMETER ARAMETRICALLY-ENHANCED UCLEAR MAGNETIC RESONANCE PECTROMETER PROpdf
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2021-08-31 | 1积分 | 319.46KB |  33 次下载

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标签: NMR

NMR

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Nuclear magnetic resonance (NMR) is a phenomenon discovered relatively recentlyin 1945, and has revolutionized medical imaging and chemical analysis since. Nuclei withnon-zero spin, such as protons, have an intrinsic magnetic moment and spin angularmomentum that can be manipulated using an externally applied static magnetic field.\r\nNuclear spins preferentially align with the static magnetic field DE to lower their energystate, resulting in a bulk spin magnetization in the field direction. When an appropriateoscillating magnetic pulse is applied, the nuclear spins can be reoriented perpendicular tothe direction of DE. Because of their intrinsic spin angular momentum, nuclear spinsprecess about DE before dephasing and returning to equilibrium parallel to the direction ofthe static magnetic field. This phenomenon is termed Larmor precession. Using a sensitivemagnetic coil perpendicular to DE, the precessing magnetization from the nuclear spins canbe detected. The properties of the signal, such as relaxation time, can be used tocharacterize the sample under analysis. [1]The high cost of the equipment to generate the intense static magnetic field,however, has been a major deterrent to the widespread adoption of NMR technology. Thehomogeneity of DE is directly related to the spectral resolution of the NMR signal, whichalso contributes to the cost. The Bruker BioSpin AVANCE 1000 NMR spectrometer, whichincorporates the world’s strongest superconducting NMR magnet at 23 T, has a list price of11.7 million Euros. [2]The Earth produces a magnetic field that can be utilized as the static magnetic fieldin NMR measurements, in lieu of an externally generated magnetic field. The strength of theEarth’s magnetic field varies approximately from 30 μT near the equator to 60 μT near thegeomagnetic poles. [3] The strength of the Earth’s magnetic field on the University ofBritish Columbia Vancouver campus (49°15'59", –123°15'13") is approximately 55 μT. [4]

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