This is a description on cloud chamber and bubble chamber in my book:

energetic charged particles cause ionization in any material they pass through. In cloud or bubble chamber, the ionized molecules along the charged particle's path form centers for the formation of tiny liquid water drops and tiny hydrogen gas bubbles respectively. These can be illuminated and photographed.

What do they mean by "form centers"?


1 Answer 1


They mean that the ionized molecules become the "seed" or "basis" or "nucleus" (= form centers) for the formation of tiny liquid water drops / bubbles.

The drops / bubbles can easily form around some "seeds" (centers). Ionized molecule is enough to become such a "seed".

  • $\begingroup$ The process is called nucleation. The wiki page has some other examples: en.wikipedia.org/wiki/Nucleation $\endgroup$
    – BMS
    Dec 6, 2013 at 13:33
  • $\begingroup$ @mpv: I just want to get one thing clear... the charged particles are not the "seeds", the molecules they ionize (the ionized molecules) are what act like centers? $\endgroup$
    – Eliza
    Dec 6, 2013 at 13:35
  • $\begingroup$ @Eliza Yes, that's correct. $\endgroup$ Dec 6, 2013 at 13:44
  • $\begingroup$ @Eliza: Yes, the seeds for the bubbles are the ionized molecules. Not the primary charged particles. The primary particles are not detected directly. They just knock electrons from molecules here and there as they fly through, thus forming the nucleation centers for the bubbles. $\endgroup$
    – mpv
    Dec 6, 2013 at 13:44

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