let's look back at the history of the discovery of NMR. 1946, Harvard scientists (Purcell, Pound and Torrey) along with Stanford scientists (Bloch, Hansen and Packard) discovered the ability of proton and phosphorus-31 (1H and 31P) nuclei to absorb radiofrequency energy when they were affected by a magnetic field with the strength typical of all atoms. At the moment of absorption, the nuclei began to intensify, with both chemical elements having their own frequency. In view of this observation, it became possible to conduct a detailed study of the structure of the molecule. Since then, NMR has been introduced for kinetic and structural analyses of bodies in the three aggregate states, resulting in six Nobel Prizes.
It has long been known that the composition of the nucleus of an atom is made up of nucleons. Each particle (proton and neutron) has its own characteristic moment of momentum - spin, characterized by quantum numbers I, and in the magnetic field by numbers m. With an even number of particles, atomic nuclei have spin = 0, and all others have spin ¹ 0. The magnetic moment of a molecule with spin ¹ 0 is μ = γ I, where γ is the gyromagnetic ratio.
The bottom line is that the magnetic moment of the nucleus forces the nucleus to manifest itself as a tiny magnet. There can also be no external magnetic field, in which case all magnets will have a random orientation. When the NMR experiment is performed, the model is placed in an external magnetic field of B0, which causes the rod magnets with weak energy to straighten toward B0 and with strong energy to straighten in the opposite direction. This leads to orientation changes. To understand this principle, consideration of the energy levels of the nucleus in the NMR experiment is required.
It takes an integer number of quanta for a spin to flip. Each number m has 2m + 1 energy levels. A nucleus with spin ½ has 2 energy levels: the first is low (occupied by spins that are in alignment with B0), the second is high (occupied by spins that are back to B0). The energy level is found by the formula: E = -mℏγB0, where m is the magnetic quantum number, in this case +/- ½.
The energy difference of levels is found by the expression: ΔE = ℏγB0.
The main condition for resonance to occur is spin reversal between energy levels. The energy of electromagnetic radiation is equivalent to the energy difference of two states and forces the nuclei of elements to change their inherent energy levels. Many NMR spectrometers have a B0 order of 1 Tesla (T), and γ is 107. It follows that the necessary electromagnetic radiation has an order of 107 Hz. The formula E = hν describes the photon energy. From this we get the required absorption frequency: ν = γB0/2π.
Please, don't forget to properly format the citation:
Panosyan V.A. Nucleus MAGNETIC RESONANCE AND APPLICATION IN TECHNOLOGY // Student: electronic scientific journal. 2021. № 17(145). URL: https://sibac.info/journal/student/145/211116 (accessed 18.05.2021).
