Classical NMR (7) Flashcards
What is the physical basis for nuclear precession?
force applied by an external RF field to dipole moment along the axis of the rotation causes dipole movement in the plane perpendicular to B0 field direction. The axis of the rotating particle moves in a circular motion
Why do nuclear spins precess in the presence of an external magnetic field?
dipole moment movement along the axis
What is the Larmor precessional frequency?
The frequency of the precession of a spinning nucleus in an applied B0 magnetic field
How can you predict the direction of precession in Larmor?
the sign of γ; γ<0 = counterclockwise, γ>0 = clockwise
Where does the resonance in the term “nuclear magnetic resonance” come from?
if RF radiation has the same frequency as that of the precessing particle, it can interact coherently with the particle and energy can be exchanged…this is resonance
What is the relationship between ∆E and Larmor frequency?
∆E = hv
How is the Larmor frequency related to magnetic field strength?
directly proportional
What is M0, the bulk or net magnetization vector?
addition of the z components of all of the nuclear magnetic dipole moments pointed along the +z direction
Is there net magnetization in the transverse plane?
nope
What is the relationship of the angle of precession to the energy of a precessing nucleus?
when energy is absorbed, angle changes
How can the angle of precession be changed?
addition of small secondary magnetic fields applied at right angles
Why is B1 applied to the x-y plane?
supplies energy for rotation
What happens to the net magnetization in the z axis as a function of time?
varies
What is a saturated state?
ground and excited states equally populated by absorption, so absorption signal decreases to 0
Does a saturated state produce an NMR signal?
nope
