Dear Spinlanders
We are experiencing serious instability problems with our Oxford 500 magnet.
In solids as well as in liquids the line shifts with 10 -15 ppm during one
day (proton shifts with ~ 6 kHz, carbon ~ 2 kHz). In liquids such shift
can be associated with fluctuation in z0 current (like when the lock is
lost and z0 does not know what to do) but in solids z0 is set to 0 and not
used.
Once such instability happens it takes several weeks for the magnet to
calm down.
Initially we thought that the instability is caused by heavy construction
around the building, however recently such instability occurred again but
there were no constructions.
Instead both times we notice such instability was after we did some low
temperature measurements (at -80 Celsius).
Would be possible that the low temperature inside the bore to affect the
cryoshims?
Please let me know what would be the best approach for this problem
Any help is much appreciated.
Sincerely
Dinu Iuga
NMR Facility Manager
http://www.uleth.ca/fas/phy/extra_content/nmr/index.html
University of Lethbridge
4401 University Drive
Lethbridge, T1k 3M4, AB, Canada
Received on Tue Dec 06 2005 - 16:20:25 MST