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    • #14863
      Profile photo of Andrew Normand

      I’ve been building cloud chambers on and off for the past couple of years, and demonstrated both ours and the de-luxe version built by Cristina Lazeroni at Birmingham University  ( at the Royal Society Summer Science Fair: my dear, the crowds!).  Success does vary, depending on lighting and ease with which viewers can get themselves into position to look at the sources.

       

      In the last couple of weeks, I’ve run a workshop for PGCE students, a demo for a school science club and another workshop for teachers.  The first two worked fine but the last was a flop.  Neither a chamber that I had made nor one made by a teacher at the worshop showed a single track.  I used the usual Th rod (2.4 mm dia) and a plastic drinking straw filled with low-sodium salt (contains traces of K-40 and so is a beta emitter).  We added the (admittedly elderly) school alph source.  Not a sniff of a trace.  Disturbing the chamber produced the usual condensation in eddies acoss the steel tray, so the basic diffusion/saturation was working.

       

      The thing is this.  At some time in the past I foolishly agreed to run the cloud chamber workshop at the Rugby meeting.  When I took Cristina’s cloud chamber there a couple of years ago it did not do brilliantly well in the rather bright lighting.  I do not want to have people feeling that they have wasted their time if they attend this workshop.  Has anyone else had a similar complete failure, and has anyone got any suggestions for avoiding it?

    • #14864
      Profile photo of Andrew Normand

      Geoffrey Heywood did this recently and got all 7 to work.  (I’m replying as I know he is away.)  I don’t know whether he used the box or  his own materials, however as he is a new PNC I’m almost certain he will have ordered new rods and not used left overs from an earlier session.

    • #14865
      Profile photo of Andrew Normand

      I’m stuck for a suggestion given that you’ve done the workshop many more times than me! Have some movies of the thing in action?

    • #14866
      Profile photo of Andrew Normand

      I’m intrigued by the plastic drinking straw so if anybody is reading this elderly thread and knows could you explain? We don’t have dry ice but use a peltier cooled cloud chamber. I use a piece of thoriated welding rod as a source but I’m curious about the lo salt. I do have some for use as a demo with a GM tube but assumed it would just get wet and be a nightmare in a cloud chamber. Do you seal it in the plastic drinking straw?

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