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First of all let us see which nuclei may be used for an NMR measurement. The first consideration is that in general there is more than one isotope for each atom and the fundamental prequisite is that the chosen isotope does possess a non zero spin, since this quantity ranges in practice from 0 to 9/2.
So, how is receptivity defined? When we apply a large static field to a non magnetic sample its nuclear magnetic moments respond to the field independently, to a very good approximation, behaving like the ideal paramagnet. Hence the equilibrium nuclear magnetization is given by the Curie law:
where is the density of atoms and is the natural abundance of the selected isotope. The electromotive force across the pick-up coil will be proportional to the derivative of M(t), hence: