The Griffith Observatory Cosmic Ray Spark Chamber was refurbished by Peter Halverson in 2005/2006.

Click on "Files" to access engineering files from the refurbishing activities. If you have questions, please do not hesitate to ask me.

By the way... I have in my garage a few parts for the spark chamber, including the trigger PC board.

I'll try to add more information here, as time permits.

Link to Griffith Observatory Cosmic Ray exhibit:

More comments:

The current setup has only two scintillator/PMT assemblies. This means that the triggering is based on two-fold coincidence. A possible improvement to the spark chamber would be to add a third PMT/scintillator for three-fold coincidence. This might improve the ratio of good to bad triggers for a more satisfying display. On the other hand, I have noticed that scintillator puts out a very bright flash of light (bright for a PMT, that is) when a particle passes through, so there isn't much confusion as to what's a valid event.

Also, during the first week of operation, the spark chamber had a very good ratio of good to bad tracks. But after that the number of tracks that were stuck on the edges of the plates dramatically increased. I think the problem is deterioration of the Glyptol insulating paint on the edges of the plates. If that is the case,then the solution to this problem would be to change the geometry of the plates so that the insulating paint is not needed.

(A good track means that you can see a nice alignment of sparks indicating the passage of a cosmic ray. A bad track is when you see random sparks or a spark on the edge of the plates.)