NMR terminology — comparing precession, transition, and Larmor frequencies In magnetic resonance, the terms “frequency of precession,” “transition frequency,” and “Larmor frequency” are best regarded as:

Difficulty: Easy

Correct Answer: Different terms for the same frequency

Explanation:


Introduction / Context:
Nuclear spins in a static magnetic field precess at the Larmor frequency, which also corresponds to the resonance (transition) frequency for absorption/emission of RF energy. Clarifying this equivalence helps students connect classical precession with quantum transitions in NMR and MRI.


Given Data / Assumptions:

  • The Larmor frequency is gamma * B0, where gamma is the gyromagnetic ratio and B0 the static field.
  • Resonance occurs when the RF field is at this frequency, enabling transitions between Zeeman energy levels.
  • Classical and quantum descriptions are consistent for spin dynamics.


Concept / Approach:

Classically, magnetization precesses about B0 at omega0 (Larmor). Quantum mechanically, the energy gap between spin states corresponds to a photon of frequency nu0 = omega0 / (2 * pi). Thus, the precession frequency and transition frequency are the same underlying quantity expressed in consistent frameworks. Different terms reflect perspective, not different values.


Step-by-Step Solution:

Relate classical precession to Larmor frequency (omega0 = gamma * B0).Relate quantum transition energy to frequency (DeltaE = h * nu0).Equate nu0 with omega0 / (2 * pi) at resonance.Conclude that all terms refer to the same frequency.


Verification / Alternative check:

Experimental resonance peaks occur exactly at the Larmor frequency computed from gamma and B0, validating equality of transition and precession frequencies.


Why Other Options Are Wrong:

Options C, D, and E incorrectly imply distinct quantities or no relationship. Option B is redundant wording; option A precisely states the equivalence.


Common Pitfalls:

Confusing angular frequency (omega) with linear frequency (nu); they differ by 2 * pi but describe the same resonance.


Final Answer:

Different terms for the same frequency

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