Аннотация
A derivation is given of the effect of a time-dependent magnetic field
gradient on the spin-echo experiment, particularly in the presence
of spin diffusion. There are several reasons for preferring certain
kinds of timedependent magnetic field gradients to the more usual
steady gradient. If the gradient is reduced during the rf pulses,
H1 need not be particularly large; if the gradient is small at the
time of the echo, the echo will be broad and its amplitude easy to
measure. Both of these relaxations of restrictions on the measurement
of diffusion coefficients by the spin-echo technique serve to extend
its range of applicability. Furthermore, a pulsed gradient can be
recommended when it is critical to define the precise time period
over which diffusion is being measured. The theoretical expression
derived has been verified experimentally for several choices of time
dependent magnetic field gradient. An apparatus is described suitable
for the production of pulsed gradients with amplitudes as large as
100 G cm-1. The diffusion coefficient of dry glycerol at 26��1�C
has been found to be (2.5�0.2)�10-8 cm2 sec-1, a value smaller than
can ordinarily be measured by the steady gradient method.
Пользователи данного ресурса
Пожалуйста,
войдите в систему, чтобы принять участие в дискуссии (добавить собственные рецензию, или комментарий)