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

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CHAPTER 8
MEASUREMENTS ON VANADIUM, NIOBIUM AND CADMIUM METALS
8.1 INTRODUCTION
In practice the number of metals which can usefully be investi-
gated using the magic angle rotation technique is limited. Although
the more common metals all possess at least one isotope with a
nuclear magnetic moment, the natural abundance of many of these is
extremely low. This fact combined with low values of magnetic
moment- means that the resonances of a number of isotopes are extrem-
ely weak. Such isotopes are unsuited to the macroscopic rotat-
ion technique using existing equipment: indeed for many isotopes
the resonance condition lay outside the range of the spectrometer.
For those nuclear isotopes with spin greater than } existing in non-
cubic lattices, quadrupole interactions lead to very broad character-
istic spectra. Of those metals with cubic or near cubic lattice
symmetry scandium, ß-manganese, tantalum and thallium still have
too large a -static
linewidth to be narrowed completely by the rotat-
ion rates which can be achieved at present. In the other extreme,
at room temperature the secular line broadening interactions in the
alkali metals are already reduced by diffusional motion. The room
temperature linewidths of lead and platinum arise in large part from
T1 broadening, which is unaffected by macroscopic specimen rotation.
Consequently these two metals were also excluded from the list of
possible samples.