NNR IN RAPIDLY ROTATED METALS By - Nottingham eTheses ...

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5.7.1 THE SOLID ECHO PULSE SEQUENCE
For a dipolar coupled spin system it may be shown (70,71)
that at resonance the transient response following a 90-T-9090
pulse sequence is given by the power series
(t' - T)
M*(t' - T) =1-M
2+M
(t' - T) 4+M
6t' 2T2
-
y22.4 4.4E 4!
t' is the time measured from the second pulse, T is the time between
the two pulses and M4E is an error term defined by Mansfield
It follows from equation (2.20) that when the product t'T is small
the response following the second pulse closely resembles the FID.
In practice the pulse lengths and the detection axis of the
PSD were adjusted for maximum signal. The phase of the second
pulse was set so that the response from a single such pulse was
zero, and T was fixed so that the echo maximum occurred immediately
after the dead time of the second pulse. The echo shape was then
recorded with the signal averager.
5.7.2 JEENER AND BROCKAERT 'ZERO TIP-1E' SEQUENCE
The results obtained from the aluminium samples with the
solid echo sequence were confirmed in part by using a
90 90 t-90_90-T-90 90 pulse sequence. In this sequence the magnet-
ization in the rotating frame My(t) is transferred back to the z
direction by the application of the second pulse 1800 out of phase
with the first. After a time T> T2 the transverse magnetization
has disappeared so that, providing T« T1, the amplitude of any
(71)
0
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