19
Pumping with a two-stage rotary pump that has a base pressure of about 10
-3
mbar is
sufficient. A diffusion pump or turbo pump would also be suitable.
5.7
Calibration of Sample Temperature
Precise estimation of the temperature of a real sample in the cold jet is not
straightforward, as it will be affected by the size and location of the sample, the
orientation of the nozzle, and by heat conduction along the sample support. Contact
Oxford Instruments for calibration information.
5.8
Stability
The temperature displayed is normally stable to about 0.1 K. Small fluctuations in
temperature will occur when the dewar is refilled.
5.9
Icing of Crystal Support and Goniometer
The shield flow is designed to prevent icing of the sample and nozzle. A slight build-up of
snow is likely on the crystal support and goniometer. In most cases no action need be
taken, provided that the incoming beam can be collimated to exclude any ice on the
crystal support. Increasing the shield flow rate to 10 l/min for a minute or so may help to
remove frost from the crystal support.
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