PulsedNMR - After a 90 degree pulse the magnetization M...

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Pulsed NMR T 1 Longitudinal (Spin-Lattice) Relaxation to B 0 direction T 2 Transverse (spin-spin) Relaxation. Dephasing of spins in the xy plane. T 2 * This includes the effect of inhomogeneous B 0 field. Therefore < T 2 After the magnet B 0 is turned on the spins reach the equilibrium population distribution with a characteristic time T 1 . There is then a net magnetization in z direction. After a 180 degree pulse the magnetization is anti-aligned (higher energy state). It returns to the equilibrium state with a time constant T 1 . If there is a pickup coil in the xy plane to detect precession no signal is seen.
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Unformatted text preview: After a 90 degree pulse the magnetization M, rotates into the xy plane and then will precess around B . A signal is detected which decreases in magnitude with characteristic time T 2 *. The damped oscillating signal is called Free Induction Decay (FID). A sequence of pulses can be applied; this can be used to measure T 1 and T 2 . A particular sequence results in a spin echo signal in which the effect of the non-uniform magnetic field is removed. See the article from Physics World....
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