Seliger J
Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, Slovenia.
Solid State Nucl Magn Reson. 1997 Aug;8(4):207-17. doi: 10.1016/s0926-2040(97)00011-8.
A new NQR method of measuring the spectral density of slow motions in solids is proposed. It is shown that also in NQR a 90 degrees phase shift of a resonant rf magnetic field following a 90 degrees pulse locks the nuclear magnetization in a 'rotating frame' similarly as in NMR. The spin-lattice relaxation time T1 rho of the locked magnetization is calculated in general for an arbitrary spin. It is assumed that the fluctuations of the EFG tensor dominate the spin-lattice relaxation. The calculations show that T1 rho depends on the spectral density J(omega) of the electric quadrupole fluctuations at the NQR frequencies, and also at a low frequency omega. Here omega approximately gamma B1 kHz depends on the orientation of the rf magnetic field in the principal-axis system of the EFG tensor. The term containing J(omega) in the expression for T1 rho-1 depends on the orientation of the rf magnetic field in the principal-axis system of the EFG tensor, only through the orientation dependence of omega. This term vanishes when the electric quadrupole fluctuations do not modulate the frequency of the NQR transition excited by the rf magnetic field. Two particular examples: I = 1 and I = 3/2 are worked out in details.
提出了一种测量固体中慢运动谱密度的新的核磁共振四极共振（NQR）方法。结果表明，在NQR中，继90度脉冲之后的共振射频磁场的90度相移同样会像在核磁共振（NMR）中那样，将核磁化锁定在“旋转坐标系”中。一般针对任意自旋计算锁定磁化的自旋 - 晶格弛豫时间T1ρ。假设电场梯度（EFG）张量的涨落主导自旋 - 晶格弛豫。计算表明，T1ρ取决于NQR频率处以及低频ω处电四极涨落的谱密度J(ω)。这里ω≈γB1kHz取决于射频磁场在EFG张量主轴系中的取向。T1ρ - 1表达式中包含J(ω)的项仅通过ω的取向依赖性取决于射频磁场在EFG张量主轴系中的取向。当电四极涨落不调制由射频磁场激发的NQR跃迁频率时，该项消失。详细给出了两个具体例子：I = 1和I = 3/2。
