Ionizing radiation, as I've learnt it, ionizes an atom by supplying enough energy to essentially "knock" an electron off the atom — that is, by exciting the electron to a level that is gets freed from the atom it was previously bound to. However, I had this belief contested by a Youtube video, whose host said that:
[...] (the argon) atom can be made negatively charged by having an electron put on it [...]
How does that work? How can radiation negatively ionize an atom, not through the removal of a proton (like is discussed in this thread) but rather by the addition of an extra electron (or more)?
The entire context here is about ionizing radiation and how it could ionize an atom (in this case, Argon) negatively so an answer explaining that would be perfect.