[3dem] How close can a high-end 300kV FEG TEM be installed next to an 800MHz 15-year old NMR machine

docdave50 at aol.com docdave50 at aol.com
Sun Feb 20 21:21:22 PST 2011

Hi Henning,
One of the suggested comments is measurement.  When the Tecnai 20 scope was installed at Yale in the Medical School, little if any attention was paid to the fact that there were pipes running in a crawl space under our floor.  When Fred Sigworth decided, one day, to off-handedly check on any fields that might affect the new scopes performance, what to our wondering eyes did appear but a 200 mGauss Magnetic Field coming from the metal pipes under the floor as a function of an electrical short which no one at Yale could find...hard to get into those crawl spaces.  Needless to say, our microscope was to be put here.  Tests were done by the FEI folks to verify the field strength and a "wait and see" attitude was taken by someone along the line.  Needless to say, a Field Compensation Device had to be installed because of this field.  One thing that was noted was that the field was not constant and, therefore, the oscillatory field strength could have been a contributing factor.  In terms of distance, this would likely have been within but closer to the 7 m distances others have talked about.  Hence, my advice is to insist on the largest possible distances between these two sources such that there is no possibility of any electromagnetic field strengths affecting image resolution with your scope.
I know at Yale, little discussion appeared to precede someone's decision to install a generator with sizeable potential field strength adjacent to our EM facility.  My advice would to error on the side of caution unless the NMR folks want to provide...in writing...the costs for field strength isolation cage for your EM facility such that there is a guarantee of unwavering limitations on maximum resolution capabilities of your scopes due to fields coming from that facility.  
A question for some of the respondents to Hennig's question where you have field compensators between you and the NMR source; if you turned off your field compensators and then looked at one of the resolutions standards, do you see any interference?  That would answer his question directly, I would think.  It should be a quick experiment and yield a vital answer to his dilemma.  Henning, I don't remember what scopes you have off hand...have you contacted the manufacturer of your scopes and asked them about the minimum requirements necessary for the 5% variance they test for in equipment functional resolution?  I do know that FEI provided clear guidelines for us on our Tecnai 12 and 20 installations...and they were concerned about aberrant field strengths once identified.
Hope this helps,

David W. Chester, Ph.D.
Currently unemployed (Structural Biochemist/Biophysicist, Cryo-EM, X-ray, Lipid Biochem/Biophysics, Methods Development)
(203) 213-4167
docdave50 at aol.com
LinkedIn Profile: http://www.linkedin.com/pub/david-w-chester-ph-d/1b/491/738 
Visiting Research Faculty
Department of Cellular and Molecular Physiology
Yale University School of Medicine
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New Haven, CT.  06520

How close can a high-end 300kV FEG TEM be installed next to an 800MHz 15-year old NMR machine? If both are on the same floor, then the magnetic field lines from the NMR should run through the TEM column vertically, so that the sensitivity for the strong DC fields of the NMR machine might be less ? 

I would appreciate any experience or recommendations, also directly towards me. 



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