We have a Magnex supercon (400/54 Year-hold circa 1996) used with a JEOL
Lambda 400 NMR spectrometer.
We have a problem that seems like field drift: lock was lost and the usual
value of Z0 required to lock onto the sample has changed drastically.
As of yesterday, boil-off of liquid helium was only slightly above normal
(220 mL/min). This morning it was 280 mL/min and has slowly climbed to 350
mL/min at noontime.
I turned off then disconnected the RT shims, and tried to obtain the
spectra of 10% H2O in D2O. I notice that the drift is very bad: using
single-pulse acquisition and peak picking of the water peak, the peak
position has changed -1486 Hz in the course of 6 minutes.
JEOL Co. (Japan) has surmised that it could be a slow quench of Z0 or the
main magnet field, although nothing unusual has happened to the magnet.
Any advice is welcome!
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Edward T. Chainani Nuclear Magnetic Resonance Laboratory Manager
National Chemistry Instrumentation Center (NCIC)
Ateneo de Manila University phone: (632) 426-6001 loc. 5629
Loyola Heights, Quezon City e-mail: etch_at_ginto.chem.admu.edu.ph
Philippines FAX: (632) 426-1323
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Received on Thu Feb 14 2002 - 08:25:18 MST