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Degaussing an MRI suite

I have been following this thread with more than just a passing interest the
last few days.  You see, my dad's job in the Navy for 20 or so years was
making our Naval fleet safe when cruising through potential mine fields.
One of the triggers for a mine is the residual magnetic signature of a ship.
To counteract this effect, following ship construction massive currents are
passed through coils wrapped around a ship to de-perm the steel.  During
ship operations, finer control of the residual magnetic field is provided by
an on-board system that monitors and corrects for residual magnetic fields
greater than 13 mT.  My dad is currently employed with a company that
manufactures these systems for navies around the world.

I thought it would be interesting to share his view on the current thread:

"I will say that Mr. Miller And Mr. Moulder are on the right track and have
referenced the
right websites. Moulder referenced Enertech; I was in contact with them
the summer to have them propose a piece of software that would predict the
magnetic signature of a ship after I did the coil design so it would display
effect of compensation, with the goal of neutralization of the overall
signature. The acceptable ship signature, by the way, is about 13
milligauss. This level
will let a ship pass safely over a mine. We are, however, striving to reduce
signatures to a level of about 8 milligauss. Anyway, Enertech is heavily
involved in power transmission line magnetic field measurement.

Finally, I gave some thought to the original question and considering that
usually the agency with this type of problem doesn't want to spend money on
something he can't see, something like the emperor's suit of clothes, the
practical solution is to shield the electronics and monitors directly
with a material known as mu-metal. While the statement that over time, the
residual fields will tend to magnetize steel structural columns and rebar is
true, the field levels are rather small,
and therefore, not a consequence. I would not permit an individual with a
pacemaker near the place. I do not know how these people are treated
but I'm sure they are not excluded from MRI treatment. By the way, the
correct spelling is "degaussing". An interesting thread you have here."

Eric W. Abelquist
P.O. Box 117
Oak Ridge,TN 37831
Tel (423) 576-3740
FAX (423) 241-3497
Email: abelquie@orau.gov 

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