In medicine, the use of nuclear magnetic resonance can diagnose abnormal tissue and determine disease. This is our familiar MRI technology. The basic principle is as follows: the nucleus has positive electricity and spin motion. Usually, the arrangement of the spin axis of the nucleus is irregular, but when it is placed in an external magnetic field, the spatial orientation of the nuclear spin transitions from disorder to order. The magnetization vector of the spin system gradually increases from zero, and when the system reaches equilibrium, the magnetization reaches a stable value.