There are a wide range of NMR experiments that can be performed with the Earth's Field NMR system. Outlined here are just some of the experiments that can be performed with the system.
Free Induction Decay: The simplest NMR experiment possible where the spins are excited by a 90 degree pulse and the resulting signal is acquired. Due to the highly uniform nature of the Earth's magnetic field the FID can be seconds long.
An FID signal from a water sample showing the long signal decay time
Spin-Echo T2 spin-spin relaxation measurement: The dephasing of the spins due to imhomogeneties is refocused by a 180 degree pulse. The amplitude of the spin echo depends on the spin-spin relaxation of the sample nuclei. The Earths field NMR experiment allows all aspects of the experiment to be controlled and the T2 of the sample calculated directly.
Figure showing how Prospa software allows all aspects of the experiment to be controlled.
Shown above Prospa can analyse the data and calculate the T2 relaxation rate from the change in signal amplitude.
Spin-Latice T1 relaxation measurement: The spin-latice relaxation of the sample can be determined by measuring the dependence of the signal amplitude of the strength of the pre-polarising pulse.
Figure above shows Prospa calculating the spin-latice relaxation time of the sample
Pulse Gradient Spin Echo (PGSE) diffusion measurement: The ability to apply pulsed magnetic field gradients allows molecular motion to be probed. A full PGSE NMR experiment can be run and the data analysed on a Stejskal-Tanner plot.
Figure showing the PGSE sequence used to measure molecular motion and self-diffusion coefficient of the sample.
Figure showing a Stejskal-Tanner plot used to calculate the self-diffusion coefficient of a sample.