Bubble Chamber

Bubble Chamber

Principle :

      We know that normally the liquid boils with the evolution of bubbles of vapour at the boiling point. If the liquid is heated under a high pressure to a temperature well above its normal boiling point. a sudden release of pressure will leave the liquid in a superheated state. If an ionizing particle passes though the liquid within a few milliseconds after the pressure is released. the ions left in the track of a particle act as condensation centres for the formation of vapour bubbles. The vapour bubbles grow at a rapid  rate and attain a visible size in a time of the order of 10 to 100μs. Thus in a bubble chamber, a vapour bubble forms in a superheated liquid. Whereas in a cloud chamber, a liquid drop forms in a supersaturated vapour. Thus an ionizing particle passing through the superheated liquid leaves in its wake a trail of bubbles which can be photographed.  

    A schematic diagram of a liquid hydrogen bubble chamber, operating at temperature of 27 K is shown in Fig 1.       

Fig 1.

   A box  of thick glass walls is filled with liquid hydrogen and connected to the expansion pressure system. To maintain the chamber at constant temperature, it is surrounded by liquid nitrogen and liquid  hydrogen shields. High energy particles are allowed to enter the chamber from the side window W.A sudden release of pressure from  the expansion valve is followed by light flash and camera takes the stereoscopic view of the chamber.

   The incoming beam triggers the chamber. The charge of the tracks can be identified by the direction of their curvature in the magnetic field applied over the bubble chamber. From the curvature and length of the track. the momentum and energy of the particle can be found. The bubble chamber is used to study particle interaction and to detect very high energy particles. 

Advantages :

 1. The density of a liquid is very large when compared to that of a gas of even high pressure. Hence the chances of collision of a high energy particle with a molecule of the liquid are very much greater.  Consequently there is a greater chance of their track being recorded. So the chances of recording events like cosmic ray phenomena are improved when compared with cloud chambers.

    

 2. The bubbles grow rapidly and as a result the tracks  are not likely to get distorted due to convection currents in the liquid.

   

 3. The bubble chamber is sensitive even to particles of low ionizing power.