sp06 - The rate at which the spins exchange energy with...

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Consequence:  NMR is not very sensitive!!
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Contrast NMR (proton) and EPR (electron) sensitivity Proton freq   42.6 MHz / Tesla     1T = 10000 Gauss Electron freq  28.0 GHz / Tesla Some numbers;   at 12T (500MHz proton NMR spectrometer)  energy sep’n = 0.017 cm -1 exp(-0.017/200) = 0.9999148 =  (1- ) /(1+ ) = 4.3 x 10 -5 at 0.3T (X Band EPR spectrometer) energy sep’n = 0.28 cm -1 exp(-0.28/200) = 0.998601  (1- ) /(1+ ) = 7.0x10 -4
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Relaxation in Magnetic Resonance Without interaction of the spins with their environment, or each  other, there would be no signal (no net magnetization) and no information in  the signal (no chemical shift).
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Unformatted text preview: The rate at which the spins exchange energy with their surroundings is characterized by a relaxation rate, k, or its inverse, a characteristic relaxation time t = 1/k. The process for relaxation of the magnetization along z (H ) requires energy exchange, whereas changing the magnetization along x or y does not. The mechanism for relaxation is therefore different and the rates are too. Longitudinal relaxation rate = 1/T 1 Transverse relaxation rate = 1/T 2 (> 1/T 1 ) The basic NMR experiment (modern era) The Hahn Spin Echo Fin...
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This note was uploaded on 05/29/2011 for the course CHM 4412 taught by Professor Brucat during the Summer '06 term at University of Florida.

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sp06 - The rate at which the spins exchange energy with...

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