Which relaxation process is associated with loss of phase coherence among spins?

• A. T1-relaxation
• B. Spin diffusion
• C. Proton exchange
• D. T2-relaxation

Answer: (D)

The key idea is transverse dephasing. After you tip the spins into the transverse plane, they no longer precess in perfect unison because local magnetic field variations and spin-spin interactions make their precession rates differ. Those tiny differences cause the spins to drift out of phase with each other, so the net transverse magnetization decays over time. That loss of phase coherence is what T2-relaxation describes.

In contrast, T1-relaxation is about longitudinal magnetization recovering through energy exchange with the lattice, not about coherence in the transverse plane. Proton exchange relates to chemical exchange processes that can affect relaxation behavior, and spin diffusion is a related phenomenon that can influence dephasing in some contexts, but the direct process responsible for losing phase coherence among spins is T2-relaxation.