View Full Version : Question about CSI:NY 1/18

2006-Jan-20, 10:02 AM
I'm not sure if this should go here or in the general science forum, since it's not astronomy related.

I tape all three CSI Shows. The original, because I think it's good, Miami, because it's total crap and I like to see just how far it will fall, and NY, because it's has yet to decide which way to go.

This last week, it took another step toward the 'Miami' way of doing things...

The killer carried a gun into a room where an MRI was being done. The magnetig field magnetied the gun and the BULLETS. They saud in the show that presence of a stong magnetic filed would magnetize metal. I know I learned back in either the 1st or 3rd grade that that metal had have iron in it, so this was really bad science that nearly everyone involved should have caught.

My question is about having a steel object near the MRI. I seem to recall a story a few years ago where and MRI was turned on while there was an oxygen tank in the room. The tank was pulled into the machine killing the patient. I think it was in Germany. How powerful are the fields, and would it be possible to draw an 80 pound object in with that much force?

Chris CII
2006-Jan-20, 12:24 PM
As for an MRI scanner magnetising the gun and bullets, that is entirely possible, because the strong magnetic fields will cause residual magnetism at least in the (ferromagnetic) gun. For the bullets I don't know, because it depends on their type.

MRI magnets are in the 0,5 - 2 Tesla in range (10 to 40 000 times stronger than earth's magnetic field) and can wreak havoc with anything ferromagnetic or magnetically encoded.
You can have look at the picture in http://science.howstuffworks.com/question698.htm
which is impressive, even if the article around is not.

2006-Jan-20, 01:42 PM
Are bullets made of copper? I don't think they are lead anymore. Anyway, I don't think copper is magnetic under normal circumstances *strains his brain*.

2006-Jan-20, 07:52 PM
Are bullets made of copper? I don't think they are lead anymore. Anyway, I don't think copper is magnetic under normal circumstances *strains his brain*.
I don't know a lot about bullet materials of construction. But copper does not become magnetic under anything close to normal circumstances. Same for lead. Even the presence of iron is not a guarantee; there are non-magnetic stainless steels.

2006-Jan-21, 07:13 AM
I don't know anything about MRI machines, but I would think the typical field ratings cited for such devices are applicable to the focused fields inside the machine (where the patient is). Stray fields on the outside of the machine are apt to be far, far less (by orders of magnitude). So that would make any effect on guns or bullets even less plausible (unless either was happened to be very proximal to the opening of the machine (where the patient would be loaded).

As far as the gun, possibly it could be constructed of a ferrous steel. Copper bullets, otoh, would not be affected by conventional magnetism, but may respond to eddy-current type of magnetism under the right conditions. My hunch tells me that neither would be affected in the described MRI scenario.