Things to keep in mind

 

1) The precession frequency of a nucleus only depends on the isotope and the magnetic field

Typical NMR magnet is ~ 15 Tesla -> protons precess at ~ 500 MHz

2) NMR measures the TOTAL magnetization M = average of billions of spins

 

3) M is small (think 10-100 people in NYC)

Boltzmann distribution:

Population at equilibrium = exp(-Energy/kT) / Sum of all {exp(-Energy/kT}

 

4) NMR is a very insensitive technique