physics

The bubble chamber consists of a tank of unstable transparent liquid - often superheated hydrogen which provides a source of proton targets - in which passing charged particles initiate boiling as a result of the energy they deposit (by ionizing atoms) as they force their way through the liquid. We see here that the bubble chamber is both target and detector: the protons are the target studied; the electrons 'detect' the passage of charged particles - via the Coulomb interaction which ionizes the atoms.

Briefly, the bubble chamber works as follows:

• The liquid is prepared and held under a pressure of about 5 atmospheres (1atm=105Pa).
• Just before the beam arrives from the accelerator the pressure is reduced to about 2 atmospheres, making the liquid sensitive to charged particles.
• The beam particles pass through the bubble chamber, some interacting, in a few nanoseconds. By the end of the bubble chamber era, bubble chambers provided a path of up to about 4 metres.
• The bubbles formed are allowed to grow for a few ms, and when they have reached a diameter of about 1 mm, a flash photograph is taken (on several views so as to enable the interactions to be reconstructed in 3-dimensions).
• The pressure is increased again to clear the bubbles and await the arrival of the next burst of particles.