Physics, Techniques and Procedures

Precession

motion performed by top and spin magnetization vectors, when the top angular momentum vector and the magnetization vector are not aligned parallel to the the gravitational force and the main magnetic field, respectively. The equations of motion of such systems predict that the top or spin axis performs a conical rotation about the gravitational or magnetic field axis (Fig.1). This motion is called precession. The precession angle f increases constantly with time, unless the system is subject to external forces. In an NMR experiment, the rate of change of this angle, the precessional frequency, is called the Larmor frequency.

GvS

Fig.1

Precession of the magnetization vector (or top axis) around the vertical (magnetic or gravitational field).

Precession, Fig.1