They are arranged in parallel in the forward or reverse order. After radio waves are applied, the spin direction of the nucleus is reversed. This is the earliest understanding of the interaction between nucleus and magnetic field and external RF field. Because of this research, Rabbi won the 1944 Nobel Prize in Physics.
1946, purcell of Harvard University and Bloch of Stanford University found that when an odd number of nuclei (including protons and neutrons) are placed in a magnetic field and a radio frequency field with a specific frequency is applied, the energy of the radio frequency field will be absorbed by the nuclei, which is a preliminary understanding of the nuclear magnetic resonance phenomenon. Because of this, the two of them won the 1952 Nobel Prize in Physics.
People discovered the phenomenon of nuclear magnetic resonance, and it soon put into practical application. Early nuclear magnetic resonance was mainly used to study the structure and properties of nuclear, such as measuring nuclear magnetic moment, electric quadrupole distance, nuclear spin and so on. Chemists use the influence of molecular structure on the magnetic field around hydrogen atoms to develop nuclear magnetic resonance spectra for the analysis of molecular structure. With the passage of time, nuclear magnetic resonance spectroscopy technology continues to develop. From the initial one-dimensional hydrogen spectrum to advanced spectra such as carbon spectrum and two-dimensional nuclear magnetic resonance spectrum, the ability of nuclear magnetic resonance technology to analyze molecular structure is getting stronger and stronger. After entering the1990s, people even developed a technology to determine the tertiary structure of protein molecule based on nuclear magnetic resonance information, which made it possible to accurately determine the molecular structure of protein in solution phase. Later, nuclear magnetic resonance was widely used in molecular composition and structure analysis, biological tissue and living tissue analysis, pathological analysis, medical diagnosis, product nondestructive monitoring and so on.
In 1970s, the appearance of pulsed Fourier transform nuclear magnetic resonance vibrometer made the application of 13C spectrum increase day by day. The analysis of substance composition and structure by nuclear magnetic resonance has the advantages of high accuracy, less restrictions on samples and no damage to samples.