Bubble Chamber

 Principle :

  We know that normally the liquid boils with the evolution of bubbles of vapor at the boiling point. If the liquid is heated under 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 through the liquid within a few milliseconds after the pressure is released. The ions left in the track of a particle act as condensation centers for the formation of vapor bubbles. The vapor bubbles grow at a rapid rate and attain a visible size in a time of the order of 10 to 100μs. 

 A box of thick glass walls is filled with liquid hydrogen and connected to the expansion pressure system. To maintain the chamber at a 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 sudden release of pressure from the expansion valve is followed by a light flash and the camera takes a 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 :

  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.

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

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

 A bubble chamber consists of a sealed cavity that is filled with a liquefied gas to reduce the inside pressure and a controlled device to maintain these gases in their liquid state. Liquid hydrogen and helium are the most commonly used liquids in the bubble chambers. For applications requiring very dense liquids, a variety of organic compounds can also be used. 

 As particles enter the chamber, a piston suddenly decreases its pressure, and the liquid enters into a superheated, metastable phase. Charged particles create an ionization track, around which the liquid vaporizes, forming microscopic bubbles. Bubble density around a track is proportional to a particle's energy loss.

 Drawbacks 

  Some of the major drawbacks of a bubble chamber include:

• Compared to newer techniques, it is inconveniently slow to operate due to the need for event reconstruction and film measurement.
•  The liquid within the chamber serves as both a target and detector, hence bubble chambers cannot be used with modern colliding-beam machines.

 Applications

 The bubble chamber is useful for analyzing high-energy particles. It is also used for measuring precisely rare decays with extremely short lifetimes