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

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wire. The tuning capacitor, identical to those used in the rotor
bosses had a tuning range of 6-30 pp. It was placed in an alumin-
ium box and connected to the coil by a short co-axial cable and a
shielded small diameter stainless steel tube. Because of the stray
capacitance introduced into the tuned circuit the inductance of
the coil was fairly critical. For the measurements of the spin-
lattice relaxation times in the cuprous halides which were performed
at 12.5 Ma z it was optimized to a value of 3.25 IH.
The rotor probe heads were designed for a 2" magnet gap. They
were constructed mainly from dural and those parts of the body near
the rf coil were coated with varnish to eliminate mechanical vibrat-
ions set up by the rf pulse. The three types of probe head used
are shown in Figures 5.4,5.5 and 5.6. Adjustment of the magic
angle was achieved in a different manner in each case. For the
conical rotor system the rotors were canted at an angle in the
box. Fine adjustment was performed by a worm drive onto the
stator mounting in the single box and a simple screw system in the
double box. In the foil bearing system the rig was adjusted in
the horizontal plane by rotation of the supporting rod.
5.5 KNIGHT SHIFT MEASUREMENTS
Accurate determinations of resonance frequencies were made by
employing the Bruker phase sensitive detector. Assuming that the
nuclear lineshape is symmetric about the Larmor frequency vo, then
from consideration of the rotating frame it can be seen that the
frequency of the reference signal may be adjusted so that the
temporal behaviour of the magnetization is observed directly. The