Cloud Chamber Trails

how can the vanishingly tiny particles that make up cosmic rays leave visible spirals and lines in cloud chambers? wouldn't those spiral trails and lines be too thin to be seen?
- gil artman (age 54)
far rockaway, ny

Nice question. In most materials, those high-energy particles don't leave a clear trail. The whole point of cloud chambers (and bubble chambers) is to create unusual conditions in which they do produce trails. In a cloud chamber, a vapor is maintained at higher-than-equilibrium density. That means that if something comes along to nucleate the formation of a liquid drop, then a liquid drop will form. The cosmic rays ionize particles they hit, triggering the drop formation. Of course there's an art to maintaining an above-equilibrium vapor pressure.

There's a little Wiki article describing this a bit further: .

Mike W.

(published on 10/31/2009)