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

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of the corresponding FID, with an apparent beat structure imposed
on top of a simple transient decay to the baseline.
As a check on the reliability of the measured second moments,
CW measurements were carried out on two purer samples (a) and (c).
The second moment values obtained in this way agreed with the
values shown in Table 7.1.
7.3.3 DISCUSSION
High values of second moment have been recorded by other
workers for specimens of thin foil and both commercial and filed
powders. The experimental second moment obtained here for the
powder filed from a pure ingot (c) is slightly higher than most of
these values, but in view of the large possible error the agree-
ment is reasonable. (One recent determination in particular put
the second moment of a6 9s pure filed sample as 12.5 G2 (15.4 kHz 2). )(110)
2
The second moment of 9.4 kHz measured from the 99.995% pure sprayed
powder (a) is markedly lower than the above values and in close
agreement with the theoretical value of 9.2 kHz2. Taken together
the tabulated results from all three samples show that the measured
second moment of annealed aluminium powder is sensitive to both purity
and the manner of specimen preparation; the implication being that
the lineshapes obtained from those specimens prepared by filing were
distorted by some form of nuclear quadrupole interaction.
Besides the anomalously high experimental second moment values,
other reported measurements have lent further support to the possi-
bility of some sort of resonant quadrupole interaction being present
in filed powder and thin foil specimens of aluminium metal. Spokas