Bubble chamber

The bubble chamber is a particle detector that makes the tracks of charged elementary particles and hadrons visible. At the same time, the filler material also serves as a target for particle collisions. The bubble chamber is similar in structure and operation of the cloud chamber.

Design and operation

A bubble chamber is usually liquid hydrogen ( alternatives such as deuterium, krypton and xenon ) filled space in which the particles to be analyzed are injected - some from a particle accelerator. Shortly before the injection, the pressure within the chamber is greatly reduced, so that the temperature of the hydrogen is above the boiling point. The incoming particles now ionize hydrogen atoms, and these ions serve as nucleation sites for gas bubbles. About 10 milliseconds after injection are triggered by a flash, multiple cameras at different positions, so that it is possible to reconstruct a three-dimensional image of traces from the photographs. Thereafter, the pressure in the chamber is increased again, so that the gas bubbles dissolve again. Overall, such a cycle takes a little more than one tenth of a second before the bubble chamber is back in the bubble-free initial state.

In the bubble chamber usually there is a uniform magnetic field, so that particles with different charge sign due to the Lorentz force curves with different curvatures toward describe ( see Fig.) From the path curvature, the ratio of mass and charge and decaying particles from the path length can determine the service life.

The bubble chamber is used as a detector and at the same time as the target of the experiment. This means that the goal of a bubble chamber experiment in general is that the injected particles interact with the filler material of the bubble chamber, so that short-lived particles such as mesons, heavy baryons or muons are produced and decay. By studying the decay products of very many similar decays can be collected (eg, spin and parity) on the crumbling particles, for example by means of a Dalitz plot further information.

History

In 1960 Donald A. Glaser for the invention of the bubble chamber the Nobel Prize in Physics. Since the 1960s included large bubble chambers to the main particle detectors. At the European nuclear research laboratory CERN were 1970-1978 and 1971-1984 Gargamelle BEBC (Big European Bubble Chamber ) in operation. Meanwhile, bubble chambers are usually only used for demonstration purposes, for modern research facilities they have become meaningless. At Fermilab is currently being tested but the suitability of bubble chambers to search for dark matter in the form of WIMPs in the framework of the " Chicagoland Observatory for Underground Particle Physics" ( COUPP ) project.