NMR Instruments - The Superconducting Magnet

When a sample is placed between the poles of the NMR superconducting magnet, the nuclei adjust their spins either with the applied magnetic field (parallel) or against (antiparallel) the direction of the applied magnetic field. RF energy is introduced to the sample through the transmitter coil surrounding the sample tube. This causes the lower energy nuclei to spin flip to the higher energy state. Once the RF energy is no longer applied to the sample, the nuclei in the higher energy state reverse spin flip to the lower energy state. This process is called relaxation. When the nuclei relax back to the lower energy state, the excess energy is emitted. This energy release is detected by the receiver coils and recorded as a modular free induction decay (FID) signal.