Low-field NMR measurement procedure when SQUID detection is used

In reported low-field nuclear magnetic resonance (NMR) measurements using Superconducting Quantum Interference Device (SQUID) detection, the pre-polarizing magnetic field has been usually oriented orthogonal to the measuring field, B_p  B_m. Melton et al. systematically analyzed the consequences of B_p decay in time after turnoff and showed that this decay should be nonadiabatic. We evaluated our measuring procedure in the light of that analysis, and found good quantitative agreement. It was showed that, when the decay time constant is comparable to the precession period of the magnetization of the sample, M, the optimum procedure is to orient B_p parallel to B_m and to apply a π/2 pulse to flip M, similar as in the case of conventional NMR.     

快速核磁共振测井实现方法的研究

测井速度慢一直是核磁共振测井所面临的主要困难之一.对核磁共振测井仪器磁体系统的设计作适当改进,无疑是解决该问题的一条有效途径. 有鉴于此,本文从理论上研究和推演出了两种快速核磁共振测井实现方法(预极化方法与加速极化方法),它们对于核磁共振测井仪器的磁体系统设计具有参考价值.计算和分析证明,采用这两种方法确实有助于提高核磁共振测井速度.