02-05 Resonance

Resonance on the nuclear scale is somewhat analogous to mechanical resonance. It is a response of an object or system that vibrates in step or phase.

A glass can be broken by the voice of a singer or a bridge can oscillate and col­lap­se when the marching rhythm of a column of soldiers or the undulation cau­sed by strong winds correspond to its own structural resonance frequency, such as the Tacoma Nar­rows Bridge across the Pudget Sound (Figure 02-08).

This correspondence of frequencies allows energy to be transferred from the external world (the soldiers' legs) to a given physical system (the bridge).

Similarly, a resonance phenomenon will occur when an electromagnetic wave of ap­pro­pri­ate frequency (equal to the Larmor frequency) reaches the nuclei; then, nuclei lo­ca­ted in the state of lower energy will be transferred to the state of higher energy.

Figure 02-08: The collapse of the Tacoma Narrows Brid­ge across the Pudget Sound in Washington state (U.S.A.; North America) in November 1940 was caused by high winds making the structure os­cil­la­te. Resonance can con­tr­ibu­te to such ac­ci­dents.

Watch a newsreel movie of this incident.