How to explain an experiment

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I'm currently in a heated argument with a classmate about a portion of an experiment we did where we placed a beta emitter on a straight line from the Geiger counter placing a magnet within the path and other where the source was 90 degrees from the counter. Understandably depending on the orientation of the magnetic high or virtually zero readings would be made.

The contention comes from the use of a gamma source. He has measured 0 counts on the 90 degree orientation. While I measured considerably more than straight line travel (this was due to the 90 degree orientation actually puts the source closer to the counter). Understandably the magnet doesn't matter here anymore. But just before this portion of experimentation we dealt with the penetration of the radiation types, with gamma of course penetrating all the thicknesses of lead available.

But the argument comes from this orientation. He says that because the Geiger counter is orientation sensitive we should not observe a reading because the radiation vector does not point into the opening of the counter. While I argue that the Geiger counter is made of plastics and metals. Easily pierced by gamma radiation. So regardless of where the source is readings will occur. As I believe the counter works through Compton events within the chamber when gamma rays enter, therefore they can enter from anywhere the radiation can penetrate.

If at all possible I would like an explanation one way or the other as what the likely event is. Thanks!
 

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A Geiger counter will generally have a detection efficiency that depends on the direction of the incoming radiation, but it shouldn't be completely insensitive in any direction. Gamma and even some beta radiation will enter it and can trigger a response inside.

There is always some chance that the gamma rays knock out an electron before they reach your magnet, so the magnet can play a role.
 

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