Kresse B, Becher M, Privalov A F, Hofmann M, Rössler E A, Vogel M, Fujara F
Institut für Festkörperphysik, TU Darmstadt, Hochschulstr. 6, 64289 Darmstadt, Germany.
Institut für Festkörperphysik, TU Darmstadt, Hochschulstr. 6, 64289 Darmstadt, Germany.
J Magn Reson. 2017 Apr;277:79-85. doi: 10.1016/j.jmr.2017.02.002. Epub 2017 Feb 4.
Field-Cycling (FC) NMR experiments were carried out at H Larmor frequencies down to about 3Hz. This could be achieved by fast switching a high polarizing magnetic field down to a low evolution field which is tilted with respect to the polarization field. Then, the low frequency Larmor precession of the nuclear spin magnetization about this evolution field is registered by means of FIDs in a high detection field. The crucial technical point of the experiment is the stabilization of the evolution field, which is achieved by compensating for temporal magnetic field fluctuations of all three spatial components. The paper reports on some other basic low field experiments such as the simultaneous measurement of the Larmor frequency and the spin-lattice relaxation time in such small fields as well as the irradiation of oscillating transversal magnetic field pulses at very low frequencies as a novel method for field calibration in low field FC NMR. The potential of low field FC is exemplified by the H relaxation dispersion of water at frequencies below about 2kHz stemming from the slow proton exchange process.
场循环（FC）核磁共振实验是在低至约3Hz的氢拉莫尔频率下进行的。这可以通过将高极化磁场快速切换到相对于极化场倾斜的低演化场来实现。然后，通过在高检测场中利用自由感应衰减（FID）记录核自旋磁化强度围绕该演化场的低频拉莫尔进动。该实验的关键技术点是演化场的稳定，这是通过补偿所有三个空间分量的时间磁场波动来实现的。本文还报道了一些其他基本的低场实验，例如在如此小的场中同时测量拉莫尔频率和自旋晶格弛豫时间，以及在非常低的频率下照射振荡横向磁场脉冲，作为低场FC NMR中场校准的一种新方法。低场FC的潜力通过频率低于约2kHz时水的氢弛豫色散得到例证，这源于缓慢的质子交换过程。
