Pretty knock-on electron (delta-ray)

Picture from CERN 2-metre hydrogen bubble chamber exposed to a beam of negative kaons () with energy 4.2 GeV. This piece corresponds to about 70 cm in the bubble chamber.

Knock-on spiralling electrons show that negative particles curve to the right.

This picture provides a simple example of a set of beam particles traveling along parallel paths without interacting with a target proton - an empty picture as far as hadron physics is concerned! The knock-on electron spiral is a spectacular side-show.

Questions:

1. How many beam tracks enter the bubble chamber?
2. Try to identify some electrons. What is the direction of the magnetic field?
3. Why do leave electrons curly tracks?
4. Why are all the electron tracks not of the same size?