I recently saw in my physics textbook a diagram of a positron and a

[Sofie1990]

i recently saw in my physics textbook a diagram of a positron and a electron being created in pair production. The diagram showed that as soon they where created, they moved in opposite directions and then they spiralled inwards a bit. Now i think the reason why they move in opposite directions is because of the magnetic field, however, if that is the case they why do they then spiral inwards? surely if it is the magnetic field, then shouldn't the electron and positron keep going in opposite directions and not be curling inwards?.
Any help would be appreciated.

 

[jtbell]

why do they then spiral inwards?

The picture you saw was probably made using a bubble chamber. The particles are traveling through some substance (e.g. liquid hydrogen), and lose energy through interacting with the atoms of that substance. As they lose energy, they also lose momentum, and the radius of curvature decreases (assuming the strength of the magnetic field stays constant).

 

[Bob S]

(Same as ltbell) See http://www.alternativephysics.org/book/MatterEnergy2.htm

When a positron and electron are created (by a photon) in the Coulomb field of a nucleus, they generally move away from the creation point with an opening angle between them. The angle is usually less than 90 degrees; never 180 degrees. If they were created in a magnetic field (like a bubble chamber), they would spiral in opposite directions. As they lose energy from ionization (Bethe-Bloch dE/dx) in the bubble chamber, they would spiral inward until they stop.