Perkin-Elmer MultiScope System, User Reference

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50 . MultiScope System Microscope User's Reference
5. Add another one and a half funnels of liquid nitrogen. Stand back and wait
two minutes.
This nitrogen also vaporizes as the dewar continues to cool. The two-minute
wait enables the bubbling to settle down and the pressure of the vaporizing
nitrogen to dissipate.
6. Continue to pour liquid nitrogen into the funnel, adding a little more each time
the funnel empties.
The funnel takes longer to empty as the dewar fills. This happens after two to
three more funnels of liquid nitrogen.
Because the dewar has now cooled, the liquid nitrogen does not vaporize, but
instead fills the dewar.
7. Remove the funnel and wait two minutes.
The liquid nitrogen settles down and bubbling slows.
8. When the nitrogen stops bubbling, refit the detector cap.
The filled dewar cools the MCT to the correct operating temperature for at
least eight hours. After that, the dewar begins to return to room temperature,
and the preamp switches off power to the MCT.