More GM responses, this time constant magnetic fields

[Don Price <dprice@magnus.acs.ohio-state.edu>]

First, allow me to send a thank you to all who responded to my question on 
collodion.

Here's a situation I observed recently, I was doing a survey of some equipment
placed in the same room as a MRI unit.  -Wait- I CAN say NMR here can't I?

This particular unit is used for research, not human imaging, and has a field
strength of aprox. 4.7 Tesla (Teslas?).  The room has colored areas of the 
floor around the unit indicating relative hazards by and to the magnet.

Some of my readings were attempted within the region around the magnet where
magnetic cards, such as credit cards, will be scrambled.  As I approached 
the "red" area, the innermost marked region, the meter stopped responding.
No audible clicks, and the needle dropped to zero.  This makes sense, when
you think of a GM as a sort of linear accelerator, or rather, an electron
accelerator.  The external magnetic field interferred with the conditions
inside the probe, and the meter stopped responding.  The effect seemed to
vary with distance from the magnet, as well as geometry, in terms of how
the GM was "pointing" with respect to the magnet.

Has anyone else seem this, and are there types of portable instruments
that may be more resistant to this?

This is more of an oddity, rather than a cricial issue, as I do not expect
to have to do this again anytime soon.  

Don Price                       dprice@magnus.acs.ohio-state.edu