DYNAMIC NUCLEAR POLARIZATION [D.N.P.]: ELEMENTARY EXPOSURE TO THE PHENOMENON OF DNP
Within a single experimental specimen there could be several spin species ensembles present. In a strong externally (external to the specimen) applied magnetic field, every one of the spin ensemble would be in equilibrium with the lattice (non-spin quantized levels of various degrees of freedom) and attain thermal equilibrium populations governed by the Boltzmann distribution for the corresponding quantization of energy level differences. In a Nuclear Magnetic Resonance, of the several nuclear species, one of the species is selected to apply the RF radiation at frequency corresponding to energy level difference of one of the species namely electron, proton, carbon, nitrogen, phosphorus etc. As a variation, it is possible to saturate the levels of one spin species. That is, by a high power RF radiation the RF induced transition rates can be increased so that the populations almost equalize. This would be a non-thermal population difference. Since this is part of the lattice of some other spin species, its population distribution can be affected. Presence of such a non thermal population difference can cause non-thermal equilibrium in another spin ensemble in the specimen. When such non-thermal equilibriums attain a steady ate, then what is called Dynamic Spin Population exists. In general when it pertains to nuclear ensembles it is referred to as Dynamic Nuclear Polarization. The description of such Dynamic Nuclear Polarization, and the enumeration of a variety of experiments involving Dynamically Polarized nuclear states are the subject matter to be included in this contribution.
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