Thanks to all who responded and gave us much food for thought.
Douglas W. Lowman
Principal Research Chemist
Telephone: (615) 229-4728
FAX: (615) 229-4558
Internet: dwlowman@emn.com
Eastman Chemical Company
Research Laboratories
P. O. Box 1972
Kingsport, TN 37662-5150
============================
>We are in the planning stages of installing a 500 MHz high-resolution NMR.
>Our installation is planned for the second floor. The concern I want to
address
>in this mail message relates to shielding the vertical stray magnetic field
>from an office area on the first floor. We estimate that the 5 G line will
>cross a person standing below the magnet in the upper chest, neck and head
>region. Does anyone have any experience in shielding stray magnetic fields
>with metal plates? Are there reasonable methods available to accomplish the
>shielding or at least significantly reduce the stray fields?
>
>If you will respond to me directly, I will summarize the comments and send
>them back out.
>
****** Response #1 --
We tried this early on with an aluminum plate for a Bruker AM-400 to shield the
magnet from trunk power lines buried in the floor. Although this is the
reverse of what you wish to do (i.e., shield something from the magnet), it
was rather
naive on our part. The flux lines (rf or magnetic) need to be completed at
some point in space. You can shield RF, but you do so only with a cage.
The magnetic flux might be shielded with mu-metal, but I believe you will
simply concentrate flux at the edges of the plate. To effectively shield
I believe you need to build a cage (an example is the vans used for mobile
MRI). Something else to be aware of....Two years after we installed our
400, the ASU decided to build a MacIntosh computer lab in the room above
the NMR. Although the stray field did not exceed 5 Gauss anywhere in the
room, I could quite effectively locate my magnet by looking at the distortion
of the mac screens. They never could get color monitors to work in the room
within 15 ft of the magnet. I didn't know about the lab for two years.
They had
tried at least 5 different color monitors on one machine until I found out.
---------------------------------------------------------------------
Ron Nieman, Director
Nuclear Magnetic Resonance Facility
Department of Chemistry and Biochemistry
Arizona State University
Tempe, Arizona 85287-1604
(602) 965-3613
Fax (602) 965-2747
email: nieman@asuchm.la.asu.edu
--------------------------------------------------------------------------------
****** Response #2 --
We have 4 spectrometers in the basement (3x500, 1x600)
We have shielded them to the floor above to have < 2 Gs at desk
level so that computer displays can be color corrected.
We are presently installing a 400 in the attic and are
installing a shield for the floor below.
The basic shield consist of magnet steel layers, 6 to 8
layers .6mm thick, above or below the magnets. The area to cover
should be 8 ft radius from the magnet center or more, preferably
symmetrical.
Let me know if you want more details.
Regards Rolf
-----------------------------------------------------------------
Rolf Tschudin Any similarity between
National Institutes of Health _ the opinion expressed
Bethesda, MD. 20892 _| |_ above and that of my
USA |_ _| employer is strictly
tschudin@nih.gov |_| coincidental.
-----------------------------------------------------------------
****** Response #3 --
Our finding was that rf got concentrated to a very high level at the
edges of the plate. I just don't know what happens with magnetic
flux, but if you run into the same effect, you could have very high
magnetic fields concentrated at edges--in essence, I believe that
it doesn't do any good unless you build a cage--a very expensive
fix wih mu-metal.
Good luck.
X-Sender: nieman@asuchm.la.asu.edu
--------------------------------------------------------------------------------
****** Response #4 --
We had the same thoughts when planing the recent installation of a 500. We
were advised by some to consider lining the floor with Aluminium plates or
(expensivly) mu-metal. Others felt that this would a. be insufficient and b.
distort the field dramatically.
Ultimately, I'm afraid, we had to change the location for the
instrument.
The ony alternative would have been to site the magnet over a personal office
of a person without medical implants and label the door to that office with
warning signs. You would also have to take care about the positioning of
furniture such as filing cabinets in that room.
Sorry to sound a pessimistic note,
Graham
+-----------------------===============================================+
| Dr. Graham Barlow | tower / VAX mail: gkb1 |
| NMR Service Manager | e-mail: gkb1@york.ac.uk |
| Dept. of Chemistry | Telephone: +44 (0)1904 432506 DDI |
| University of York | Fax: +44 (0)1904 432516 |
| Heslington, YORK, UK | WWW: http://www.york.ac.uk/depts/chem/nmr |
+-----------------------+==Mime OK ====================================+
****** Response #5 --
I remember a report on last year's Bruker Germany users' meeting. They bolted a
2 cm iron (not steel) plate (4x4 m I think) to the ceiling of the room
below (a cafeteria). One comment I remember was "I'd rather sit in a 10 G
FIeld than under tons of iron". I am sure you can get more info from
Bruker. But of course there are regulations....
Norbert Mueller
Assoc. Prof. of Physical Organic Chemistry
Institut fuer Chemie, Johannes Kepler Universitaet A-4040 Linz, Austria
e-mail: NMUELLER@jk.uni-linz.ac.at (preferred)
****** Response # 6 --
Congratulations on the new purchase. You did not mention the vendor,
however the Varian App Lab at Florham Park required floor shielding and
Howard Hill and probably Chris Jones are well aware of the necessary
parameters for the shielding material, etc. Contact your local sales rep.
Good Luck, Ruth Inners, Resonance Research tel. 510-651-6768, fax
510-651-8085 and email inners@netcom.com
****** Response #7 --
> We are in the planning stages of installing a 500 MHz high-resolution NMR.
> Our installation is planned for the second floor. The concern I want to
IMHO, get those plans changed, if you possibly can. The best shielding is
distance.
The issue can have financial and legal consequences. Let's imagine, for
example, that sometime around the year 2015, a former employee of Eastman
Chemical Company who had worked in the office with the stray fields suddenly
started growing purple hair, or developed cancer of the toenail. Might the
person possibly get the idea that the magnetic fields were to blame? Might
the person decide to sue Eastman Chemical Company? Even if the suit were to
have absolutely no merit, how much money would it cost Eastman Chemical
Company to prove this? Given the large number of reports of UFO sightings,
Elvis sightings, pyramid power, the efficacy of astrology, channeling, etc.,
would the company lawyers be willing to bet that a random jury would recognize
pseudoscientific nonsense when they see it, and conclude that the suit is
indeed without merit?
Or what if someone's cardiac pacemaker burps for some reason totally unrelated
to the stray magnetic fields? Do you actually believe that the stray magnetic
fields will be assumed innocent until proven guilty?
> address in this mail message relates to shielding the vertical stray
> magnetic field from an office area on the first floor. We estimate that
> the 5 G line will cross a person standing below the magnet in the upper
> chest, neck and head region. Does anyone have any experience in shielding
> stray magnetic fields with metal plates? Are there reasonable methods
> available to accomplish the shielding or at least significantly reduce the
> stray fields?
One would think that it might be as simple as simply covering the floor,
ceiling, and walls with 1/4" steel plate, but I'm not so sure. Some MRI
installations have indeed dealt with the problem, but I strongly suspect that
the solution cost them a bundle. You might check with Oxford.
I've included the following email notes from my archives
[removed by Doug Lowman for this summary] -- Bruker Users Mail,
and AMMRL email. They all relate at least somewhat to your situation, but non
of them answer your question directly -- except to say don't try shielding if
you can possibly avoid it. Several of the notes are summaries of responses.
HOW TO MAGNETICALLY SHIELD A MONITOR
Re: Faraday cage? No?
MU TOO?
MAIL TO BE SENT TO ALL THE MEMBERS OF AMMRL
600 SITING SUGGESTIONS (LONG)
NMR STRAY FIELDS AND OUTSIDE INTERFERENCE
RE: NMR STRAY FIELDS AND OUTSIDE INTERFERENCE
MINIMUM DISTANCE OF 600 TO ELEVATORS
Does anyone know of any studies on the impact of mri or nmr spectrometers
(magnets or rf) on pregnancy? I have been told that OSHA might have
MAGNETIC FIELDS AND PROSTHETIC DEVICES
Hope this helps. -- Gerry
---------------------------------------------------------------
Gerald A. Pearson INTERNET: gerald-pearson@uiowa.edu
Chem. Dept., Univ. of Iowa VOICE: 319-335-1336
Iowa City, IA 52242-1219, USA FAX: 319-335-1270