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

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The transient nuclear signals were recorded by using the
DL 102 signal averager. In the experimental arrangement used
each scan through the 200 memory channels was triggered off the
leading edge of the gating pulse to the transmitter and the det-
ected FID following the rf pulse was DC coupled into the averager.
No on-line Fourier transform capability was available, so the cont-
ents of the averager's memory were output to the teletype and
recorded onto paper tape. Fourier transformation of the recorded
data was undertaken with the University's ICL 1906A computer. The
program used for this purpose basically operated from the numeri-
cal summation
(w) _1
I G(t) cos wt St
Second moment values were determined from the transformed spectra
by a simple summation procedure written into the computer program.
Asymmetric nuclear lineshapes such as those arising from aniso-
tropic Knight shift interactions were obtained by setting the ref-
erence frequency to the phase sensitive detector well outside the
resonance spectrum. The transient response to the if pulse was
then recorded along a single detection axis in the rotating refer-
ence frame. After a correction for the reference phase the decay
signals were transformed using the same summation procedure as
above. This results in a symmetric frequency distribution with
the asymmetric absorption lineshape mirrored about vref'
The time origin of the recorded decay shapes was taken as the
centre of the -rf pulse for all measurements. This position has
been determined theoretically(68) and was confirmed for the rotating