<P> There are different angles for the sample spinning relative to the applied field for the averaging of quadrupole interactions and paramagnetic interactions, correspondingly ~ 30.6 ° and ~ 70.1 ° . </P> <P> A concept developed by Sven Hartmann and Erwin Hahn was utilized in transferring magnetization from protons to less sensitive nuclei (popularly known as cross-polarization) by M.G. Gibby, Alex Pines and John S. Waugh . Then, Jake Schaefer and Ed Stejskal demonstrated also the powerful use of cross-polarization under MASS conditions (CP - MAS) which is now routinely employed to measure high resolution spectra of low - abundance and low - sensitivity nuclei, namely carbon - 13, in solids . </P> <P> Because the intensity of nuclear magnetic resonance signals and, hence, the sensitivity of the technique depends on the strength of the magnetic field the technique has also advanced over the decades with the development of more powerful magnets . Advances made in audio - visual technology have also improved the signal - generation and processing capabilities of newer instruments . </P> <P> As noted above, the sensitivity of nuclear magnetic resonance signals is also dependent on the presence of a magnetically susceptible nuclide and, therefore, either on the natural abundance of such nuclides or on the ability of the experimentalist to artificially enrich the molecules, under study, with such nuclides . The most abundant naturally occurring isotopes of hydrogen and phosphorus (for example) are both magnetically susceptible and readily useful for nuclear magnetic resonance spectroscopy . In contrast, carbon and nitrogen have useful isotopes but which occur only in very low natural abundance . </P>

For a nucleus to exhibit the nuclear magnetic resonance