Spark Chamber

The chamber is a series of 1/4" aluminium plates seperated with insulating spacers about 1" apart. A Helium and Neon gas mixture is slowly passed through the chamber at a slightly positive pressure. There were 2 photomultipliers looking at sheets of light shielded, scintillator plastic on top and underneath the chamber. The cosmic rays cause a flash of light which is detected by the photomultomultiplier tubes which are hooked to a discrminator and coincidence circuit which triggers a Thyraton circuit which applies the High Voltage (14,500 volts) to the chamber within 0.5 microsecond resulting in visible conduction paths along the ionization paths of the particles. The rate for the 6' x 30" x 20" volume is one event about every 10 seconds on the average.