Nuclear spin flip: Change in orientation of the nuclear spin axis upon energy absorption (excitation) or energy release (relaxation).

Orientation of applied magnetic field (B0)			Add energy (excitation) Release energy (relaxation)
		I = + 1/2 Lowest energy Ground state		I = - 1/2 Higher energy Excited state

Change in orientation of nuclear spin upon excitation or relaxation. The arrow through each nucleus indicates the nuclear spin axis (i.e., orientation of magnetic north pole created by nuclear spin).