关键词: NMR, 反转恢复测试, 辐射阻尼, T₁弛豫效应, 信号强度

Abstract: In the presence of strong radiation damping, the conventional two-pulse inversion recovery measurements have been performed on water sample(90%H₂O/10%D₂O). It shows that if two pulses in IR sequence are 180° out of phase and the flip angle of the inversion pule is smaller than 180°, or if two pulses are in phase and the flip angle of the inversion pulse is larger than 180°, the signal intensity will continuously changes with the recovery time. Conversely, if two pulses are in phase (or 180° out of phase) and the flip angle of the inversion pulse is smaller than 180° (or larger than 180°), the signal intensity will jump from the negative maximum to the positive maximum around τ=T_rdln{tan[(π±δ)/2]}. Under the off-resonance condition, no matter what pulse phase, the beating effect can be always observed, but the phase of the signal explicitly depends on the relative phase of the pulses. As a result, the phase cycling will greatly suppress the beating effect. These phenomena can be well explained by the radiation damping theory. In addition, when the magnetization locates near the-zaxis during the detection, the deviation of theoretical expectation from the experimental data is closely related to the longitudinal relaxation effect.

Key words: NMR, Inversion recovery, Radiation damping, T₁ relaxation, Signal intensity