What a great group!! I posted my problem of a background C13 signal in my
solids probe and the next day had about ten responses. I'd like to thank
those of you who responded to my query. Here is a brief summary of the
responses that I received:
1. One spurious proton signal was traced to the polyethylene in the coaxial
cable.
2. Background signal was traced to either Kel-F caps or pick up from the
co-axial cables.
3. Acoustic ringing should disappear when probe is outside the sweet spot of
the magnet.
4. Acoustic resonance tracks as if it's a real signal caused by the induction
of current in the probe shield.
5. The "ghost" signal disappeared when the console was upgraded and the RT
shim set was replaced.
6. Acoustic ringing may depend upon magnetic field (Chem. Phys. Lett. 173,
p. 481, 1990) if it originates from piesoelectric ringing of the ceramic
capacitor(JMR,A108, p. 244, 1994).
7. Magneto acoustic resonance usually blamed for broad background signal and
if its caused by the aluminum cover, then one could line the cover with
either tin or lead to reduce the problem. One hundred references can be
found at google.com .
Any miscommunications in these summaries are my fault. I would again like to
thank all of you who responded.
Tom
Tom Nakashima
Chemistry Department
University of Alberta
Edmonton Alberta
Canada T6G 2G2
e-mail address:
vnmr1_at_ultranmr.chem.ualberta.ca
Received on Wed Feb 16 2000 - 19:30:20 MST