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

which gives
K=0.048
an
± 0.002
- 117 -
Although somewhat larger than the estimate by Masuda(130), this
figure is in good agreement with the results of Rowland (129) and
of Borsaand Barnes (132) who determined Kan from a measurement of
linewidth against magnetic field.
Figure 8.2 shows the 111Cd
resonance spectrum measured with
the powder specimen spinning about the magic angle at three differ-
ent rates. The conical rotor system was employed in an applied
magnetic field of 1.45 T. Accurate adjustment of the magic angle
was performed by observation of the strong resonance signal from
a small amount of aluminium powder mixed with the cadmium. It can
be seen that the anisotropic Knight shift broadening of the reson-
ance spectrum is indeed removed by rotation at the magic angle.
As the rotation rate is increased the spinning sidebands, which are
asymmetric about v0, become completely removed from the central
spectrum leaving a residual symmetric line. The signal-to-noise
ratio of the transformed lineshapes was not sufficient to enable
the second moments of the central lines to be estimated with any
degree of certainty. However the half-height linewidths could be
determined. Although there was considerable scatter in the results
obtained at differing rotation frequencies, the width of the 113Cd
resonance line was consistently greater than that of the 111Cd.
The mean values of their residual linewidths were 800 t 100 Hz and
750 ± 80 Hz respectively. The large spread in values is assumed
to arise because of the relatively poor signal strengths and the
ad hoc assumptions made about the data points obscured during the
instrumental dead time.