What is the origin of the nuclear magnetic dipole moment (m) and how is it oriented relative to an external magnetic field B0? - PowerPoint PPT Presentation

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What is the origin of the nuclear magnetic dipole moment (m) and how is it oriented relative to an external magnetic field B0?

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Effect of various types of magnetic field inhonogeneities on the FID decay ... Why doesn't the FID decay exponentially with time. as expected from theory? ... – PowerPoint PPT presentation

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Title: What is the origin of the nuclear magnetic dipole moment (m) and how is it oriented relative to an external magnetic field B0?


1
What is the origin of the nuclear magnetic dipole
moment (m) and how is it oriented relative to an
external magnetic field B0?
2
From Quantum Mechanics (I ½-particle 1H,
13C,31P,)
z
m
q
y
f
x
3
Characterizing the motion of m in B0
m gL L angular momentum (spin)
  • m x B
  • torque

Exercise 1.1 Derive the above equation
(qualitatively)
4
Solution Larmor Equation - the basic NMR equation
w -gB
5
Conclusion
  • THE LARMOR EQUATION (w -gB) IS DERIVED FROM A
    CLASSICAL MECHANICAL APPROACH
  • THE SPIN MOTION IS WITHIN THE MHz-RANGE
    (Radio-frequencies)

6
MOTION OF m IN A ROTATING FRAME OF REFERENCE
w rotation frequency of the reference frame
relative to the static frame
7
  • Exercise 1.4. Find the solution of the above
    equation in the rotating frame, (Note w0 -gB0)

mU ? cos(w-w0)t mV ? sin(w-w0)t
8
One dipole (mi) ? Many dipoles (
)
Mxy 0 !!!!!
9
LINEAR POLARIZED FIELD B1 B1cos(wt)
Rf-irradiation
Conclusion A LPF is composed of two opposite
rotating fields
10
RFR Application of an rf-pulse along the
u-direction (Why and what effect ?)
11
Excersize 1.5 What effect will B1have on the
magnetization when on resonance (w0 w) ?
Discuss
12
a
B1
The magnetization is rotated an angle a during
the duration t of the rf-pulse
Show experiment !
13
Decaying FID? show experiment
14
Including (phenomenologicaly) relaxation terms in
the Bloch equation (RFR)
15
Bloch Equation (on resonance, after magnetization
is rotated onto the v-axis)
Solution (after the magnetization is rotated into
the uv-plane (w1 0) Exercise 2.2)
16
Water Confined between Solid Glass beads -
Experiment
17
Effect of various types of magnetic field
inhonogeneities on the FID decay Let N(B)
represent the number of spins experiencing a
magnetic field B. Since w gB, we may write dN
N(w)dw
What is the observable signal intensity M if ?
18
What if N(B)
19
Why doesnt the FID decay exponentially with time
as expected from theory? (Perform a CPMG pulse
sequence)
20
Why does the FID decay faster (1/T2) than what
is predicted by the true spin-spin relaxation
rate 1/T2?
FID
Homogeneous field
lnM
Inhomogeneous field
Time
21
Principles for Measuring T2 Spin gymnastics
Controlled sequence of rf-pulses Hahn spin-echo
p/2-t-p-t-deteksjon
(p/2)-puls
22
The basic (p/2)x p-x spin-echo experiment
23
Magnetization in the rotating frame
100 meter
24
(No Transcript)
25
EKKO
26
SPIN-ECHO-EKSPERIMENT
1/T2
1/T21/T2INH
27
CPMG-pulse sequence p/2-t-(p-t-deteksjon)n
28
T1-experiment
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