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: http://www.griffithobservatory.org/exhibits/edgeofspace_cosmicrays.html
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.)
