Would an electromagnetic field have any effect on the reading of a Geiger-Muller tube and would I get false positives or negatives if I used it to detect beta particles in an electromagnetic field?

Answer 1

Yes, you could. The Geiger-Müller tube itself is fairly immune to electromagnetic fields by virtue of its construction. It's built inside a metal cylinder, which will offer some shielding. But outside the tube, things are different. Electromagnetic fields will deflect any charged particle (like a beta particle) that attempts to move through them. The amount and direction of the deflection of charged particles that move through a magnetic field will vary as a function of the direction of the magnetic lines of force relative to the path of the particle, the strength of the magnetic field, and the polarity and strength of the charge on the particle. Beta particles are high energy electrons, or sometime positrons, and the two particles will be affected oppositely by force on them created by their relative motion through the magnetic field. The term relative motion is important because it means the particle is moving in some way "across" or "through" the magnetic lines of force, and not "along" or "parallel" with them. Our beta particles, as they are generated and begin to move toward the GM tube, will encounter "diversion force" which will deflect them away from the original path of travel. This will affect their ability to actually get into the detector (the GM tube) through the window in it. And that will affect the count. It is improbable that looking for beta (or any charged) particles in a modest magnetic field will permit an accurate reading, and the reading will be "too low" because a number of the particles will be deflected away from the window of the GM tube. There is one more thing, and that's that it's hard for particles moving in an arc (along a curved course) to "hit a window" like the one in the GM tube and go in very far. Even if they get in the window, they will "curve across" the inside of the tube very near the window, and this might not allow them to trigger a current avalanche to record a "click" or a "count" for that particle. Readings could easily be very low if the detector is being used in a fairly stiff magnetic field. A link can be found below.