Spark chamber
A spark chamber is an obsolete particle detector today . Spark chambers were used in particle physics and in gamma astronomy .
Spark chambers are u. a. suitable for the detection of muons (secondary particles of cosmic radiation ).
Structure and functionality
Several parallel electrically conductive plates are attached in an optically transparent chamber. The two poles of a high voltage of around 20 kV are alternately applied to the plates. The chamber is filled with an inert gas that is initially electrically neutral. The plates are therefore isolated from one another, no current flows.
A penetrating, electrically charged particle splits electrons from the atoms along its trajectory , leaving behind an ionization trail. The resulting ions are accelerated by the applied voltage, triggering further charge carriers like an avalanche ( impact ionization ). A spark finally leaps over between adjacent plates . The spark discharge takes place exactly along the ionization track, i.e. the trajectory. The path of the particle can be observed across several plates if these are penetrated by the particle. This is the case, for example, with the muons of secondary cosmic rays .
The response sensitivity can be regulated via the high voltage.
Usually the high voltage of the spark chamber is only applied when a particle has flown through it. This is achieved by attaching particle detectors ( scintillator detectors or Geiger-Müller counter tubes ) in front of and behind the chamber , the simultaneous response of which indicates the passage of a particle. For this purpose, they are connected to a coincidence circuit that triggers the generation of the high-voltage pulse. The high-voltage pulse builds up the electrical field between the plates so quickly that the ionization track is still present and the discharge is channeled along the track. This triggering of the high voltage supply has the advantage that no spontaneous discharges occur and the high voltage does not have to be adjustable. The triggering can e.g. B. be done by a switching spark gap that connects a charged capacitor to the plates.
The color of the discharge depends on the inert gas filling.
Today (2020) spark chambers are hardly needed in research. They are mainly used for demonstration purposes.
literature
L. Griffiths, Ch. R. Symoms, B. Zacharov: Determination of particle momenta in spark chamber and counter experiments. CERN publication, CERN, 1966
