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Chapter 2

02-01
The Basics

02-02
Magnetic Properties of Nuclei

02-03
The Boltzmann Distribution

02-04
The Larmor Equation

02-05
Resonance

02-06
Magnetization

02-07
The Rotating Coordinate System

02-08
The Magnetic Resonance Signal

02-09
Frequency Analysis: Fourier Transform


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.

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