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Chapter 3

3.3. Drop size distribution from NMR restricted diffusion measurement
3.3.1. Introduction

In the NMR restricted diffusion measurement, the pulsed magnetic field
gradient spin-echo experiment (PGSE) was developed by Stejskal and Tanner^[12].
The basic sequence consists of an rf 90^o pulse, followed by a rf 180^o pulse at time
τ. As a result of this sequence, a spin-echo is collected at time 2τ (echo spacing),
as shown in Figure 3.2 ^[5]. The rf 180^o pulse is between two magnetic gradient
pulses with strength g and duration δ that are separated by the diffusion time Δ.

90⁰         180⁰

t = 0              τ             2τ

----∆----M

Figure 3.2 Basic sequence of PGSE measurement

The first pulse makes the spins with different frequencies dependent on their
positions, encoding the phase of the spins. Then, after the 180^o pulse inverts the
precession, the second gradient pulse returns the spins to their original phase for
measurement. However, some molecules diffuse and change their position during

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