Bubble chamber

Bubble chamber

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Encyclopedia
A bubble chamber is a vessel filled with a superheated
Superheating
In physics, superheating is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling...

 transparent liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...

 (most often liquid hydrogen
Liquid hydrogen
Liquid hydrogen is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.To exist as a liquid, H2 must be pressurized above and cooled below hydrogen's Critical point. However, for hydrogen to be in a full liquid state without boiling off, it needs to be...

) used to detect electrically charged
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...

 particles moving through it. It was invented in 1952 by Donald A. Glaser
Donald A. Glaser
Donald Arthur Glaser , is an American physicist, neurobiologist, and Nobel Prize in Physics laureate for his invention of the Bubble chamber used in subatomic particle physics....

, for which he was awarded the 1960 Nobel Prize in Physics
Nobel Prize in Physics
The Nobel Prize in Physics is awarded once a year by the Royal Swedish Academy of Sciences. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895 and awarded since 1901; the others are the Nobel Prize in Chemistry, Nobel Prize in Literature, Nobel Peace Prize, and...

. Anecdotally, Glaser was inspired by the bubbles in a glass of beer
Beer
Beer is the world's most widely consumed andprobably oldest alcoholic beverage; it is the third most popular drink overall, after water and tea. It is produced by the brewing and fermentation of sugars, mainly derived from malted cereal grains, most commonly malted barley and malted wheat...

; however, in a 2006 talk, he refuted this story, saying that although beer was not the inspiration for the bubble chamber, he did experiments using beer to fill early prototype
Prototype
A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...

s.

Cloud chamber
Cloud chamber
The cloud chamber, also known as the Wilson chamber, is a particle detector used for detecting ionizing radiation. In its most basic form, a cloud chamber is a sealed environment containing a supersaturated vapor of water or alcohol. When a charged particle interacts with the mixture, it ionizes it...

s work on the same principles as bubble chambers, only they are based on supersaturated vapor
Supersaturation
The term supersaturation refers to a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances...

 rather than superheated liquid
Superheating
In physics, superheating is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling...

. While bubble chambers were extensively used in the past, they have now mostly been supplanted by wire chamber
Wire chamber
A multi-wire chamber is a detector for particles of ionizing radiation which is an advancement of the concept of the Geiger counter and the proportional counter....

s and spark chambers. Historically, notable bubble chambers include the Big European Bubble Chamber
Big European Bubble Chamber
The Big European Bubble Chamber was a piece of equipment used to study particle physics at CERN. BEBC was installed at CERN in the early 1970s. It was a stainless-steel vessel filled with 35 cubic metres of liquid hydrogen. Charged particles left trails of bubbles as they passed through it. It...

 (BEBC) and Gargamelle
Gargamelle
Gargamelle was a giant bubble chamber detector at CERN, designed mainly for the detection of neutrino interactions. Built in France, with a diameter of nearly 2 meters and 4.8 meters in length, Gargamelle held nearly 12 cubic meters of freon...

.

Function and use


The bubble chamber is similar to a cloud chamber
Cloud chamber
The cloud chamber, also known as the Wilson chamber, is a particle detector used for detecting ionizing radiation. In its most basic form, a cloud chamber is a sealed environment containing a supersaturated vapor of water or alcohol. When a charged particle interacts with the mixture, it ionizes it...

 in application and basic principle. It is normally made by filling a large cylinder with a liquid heated to just below its boiling point
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

. As particles enter the chamber, a piston
Piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...

 suddenly decreases its pressure, and the liquid enters into a superheated, metastable phase. Charged particles create an ionisation track, around which the liquid vaporises, forming microscopic bubble
Liquid bubble
A bubble is a globule of one substance in another, usually gas in a liquid.Due to the Marangoni effect, bubbles may remain intact when they reach the surface of the immersive substance.-Common examples:...

s. Bubble density around a track is proportional to a particle's energy loss.

Bubbles grow in size as the chamber expands, until they are large enough to be seen or photographed. Several cameras are mounted around it, allowing a three-dimensional image of an event to be captured. Bubble chambers with resolutions down to a few μm have been operated.

The entire chamber is subject to a constant magnetic field, which causes charged particles to travel in helical
Helix
A helix is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helixes are coil springs and the handrails of spiral staircases. A "filled-in" helix – for...

 paths whose radius is determined by their charge-to-mass ratios and their velocities. Since the magnitude of the charge of all known charged, long-lived subatomic particles is the same as that of an electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

, their radius of curvature must be proportional to their momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...

. Thus, by measuring their radius of curvature, their momentum can be determined.

Notable discoveries made by bubble chamber include the discovery of weak neutral current
Neutral current
Weak neutral current interactions are one of the ways in which subatomic particles can interact by means of the weak force. These interactions are mediated by the boson...

s at Gargamelle
Gargamelle
Gargamelle was a giant bubble chamber detector at CERN, designed mainly for the detection of neutrino interactions. Built in France, with a diameter of nearly 2 meters and 4.8 meters in length, Gargamelle held nearly 12 cubic meters of freon...

 in 1973, which establish the soundness of the electroweak theory and paved the way to the discovery of the W and Z bosons
W and Z bosons
The W and Z bosons are the elementary particles that mediate the weak interaction; their symbols are , and . The W bosons have a positive and negative electric charge of 1 elementary charge respectively and are each other's antiparticle. The Z boson is electrically neutral and its own...

 in 1983 (at the UA1 and UA2 experiments). Recently, bubble chambers have been used in research on WIMPs, at COUPP and PICASSO.

Drawbacks


Although bubble chambers were very successful in the past, they are of only limited use in current very-high-energy experiments, for a variety of reasons:
  • The need for a photographic readout rather than three-dimensional electronic data makes it less convenient, especially in experiments which must be reset, repeated and analyzed many times.
  • The superheated phase must be ready at the precise moment of collision, which complicates the detection of short-lived particles.
  • Bubble chambers are neither large nor massive enough to analyze high-energy collisions, where all products should be contained inside the detector.
  • The high-energy particles' path radii may be too large to allow the precise estimation of momentum in a relatively small chamber.


Due to these issues, bubble chambers have largely been replaced by wire chamber
Wire chamber
A multi-wire chamber is a detector for particles of ionizing radiation which is an advancement of the concept of the Geiger counter and the proportional counter....

s, which allow particle energies
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

 to be measured at the same time. Another alternative technique is the spark chamber.