Lecture 5 Summary: NMR Summary

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Lecture 5 Summary NMR Summary

• If a sample is placed in a static magnetic
  field, Bzk, there is a degeneracy of spin states
  giving rise to a net magnetisation M along z. The
  magnitude of Mz at thermal equilibrium is Mo.This
  is v. small and undetectable due to Bz. So
• Apply B1(t). 900 pulse flips magnetisation into
  transverse plane and brings spins in phase
  My Mo, Mx 0, Mz 0.
• Once B1(t) is turned off My and Mx oscillate at
  the Larmor frequency, and the signal decays as
  the spins dephase with time constant T2. Mz
  recovers to equilibrium Mo with time constant T1,
• NMR signal is detected by a receiver coil with
  its axis along y. Therefore My is detected.
  Signal is very small but is detectable as it
  oscillates at the Larmor frequency.

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