Nuclear polarization ($P=⟨J_z⟩/(I\hslash )$)

The mean orientation of nuclear spin angular momentum in a chosen direction. For nuclei with nonzero spin quantum number $I$, the vector-polarization component is $P=⟨J_z⟩/(I\hslash )$ and lies between $-1$ and $1$. Equal populations of all projections give $P=0$; complete alignment gives $P=1$.