Representation of precession of nucleus:
The precessional frequency (ω) also called Larmor frequency is directly proportional to the strength of the external magnetic field (B0). therefore
ω α B0 or ω = γB0
where, γ is called the magnetogyric (or gyromagnetic) ratio. It is the ratio of the nuclear magnetic moment (µ) and the nuclear angular momentum (I). i.e., γ = µ/I. The general frequency, ν and the precessional frequency, ω are associated as follows:
ω = 2πv = γ B0
or ν = γ/2π B0=(B0 /2π) .µ/I
After substituting values of I and µ , from Eqs. 1 and 3 respectively, we get the following expression.
ν = g N µN B0/h
Thus, the precessional frequency of the spinning nucleus is exactly equal to the frequency of electromagnetic radiation necessary to induce a transition from one nuclear spin state to another spin state. This fact gives a mechanism of causing the nuclear spin transition.
![349_Representation of precession of nucleus.png](https://www.expertsmind.com/CMSImages/349_Representation%20of%20precession%20of%20nucleus.png)
Figure: Representation of precession of nucleus in two orientations; aligned to the external magnetic field and opposed to the magnetic field