Bloch_eq_2010

# Bloch_eq_2010 - Pulse and FT NMR In practice bulk...

This preview shows pages 1–5. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Pulse and FT NMR In practice bulk magnetization is observed For isolated spins behavior is according to classical Bloch equations dM/dt = γ M X B – (M z – M ) (1/T 1 ) – M x,y (1/T 2 ) Precession in a Static Field Torque on system with angular momentum (J) causes precession of the momentum vector. dJ/dt = T. Torque is given by M X B and M = γ J. Bloch equations give precession at ω = - γ B . dM/dt = γ M(t) X B 0 x y B J = M/ γ T dM x /dt = γ M y B dM y /dt = - γ M x B 0 dM z /dt = 0 i j k dM/dt = γ M x M y M z 0 0 B 0 Solution: M x (t) = M 0x cos(- γ B t) - M 0y sin(- γ B t) = M exp(-i γ B t) = M exp(i ω t) Spin precession is like precession of a gyroscope The Rotating Frame Simplifies Analysis of RF Pulses and Small Frequency Offsets ω 0 is very high (500 MHz x 2 π ) – differences due to chemical shifts etc. are small (ppm x 500 Hz x 2 π ) Therefore, use reference frame moving near ω ....
View Full Document

{[ snackBarMessage ]}

### Page1 / 9

Bloch_eq_2010 - Pulse and FT NMR In practice bulk...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online