Bubble chamber
The bubble chamber is a particle detector that makes the traces of charged elementary particles and hadrons visible. At the same time, the filling material also serves as a target for particle collisions. The bubble chamber is similar in structure and functionality to the cloud chamber .
Structure and functionality
A bubble chamber is usually a space filled with liquid hydrogen (alternatives are e.g. deuterium , krypton and xenon ) into which the particles to be examined are injected - for example from a particle accelerator . Shortly before the injection, the pressure inside the chamber is greatly reduced so that the temperature of the hydrogen is above the boiling point. The incoming particles ionize hydrogen atoms and these ions serve as nuclei for gas bubbles. Around 10 milliseconds after the injection, several cameras are triggered at different positions by a flash, so that a three-dimensional image of the tracks can be reconstructed from the photographs. Then the pressure in the chamber is increased again so that the gas bubbles dissolve again. In total, such a cycle takes a little more than a tenth of a second before the bubble chamber is again in its initial bubble-free state.
In the bubble chamber there is usually a homogeneous magnetic field, so that particles with different charge signs describe curves with different directions of curvature due to the Lorentz force (see Fig.). The ratio of mass and charge can be determined from the curvature of the orbit and, in the case of decaying particles, from the length of the orbit. The orbits of charged particles with lower speed are wound up into spirals by the magnetic deflection, together with the gradual deceleration by impacts (in the schematic illustration on the left).
The bubble chamber serves as a detector and at the same time as the target of the experiment. This means that the goal of a bubble chamber experiment is generally that the injected particles interact with the filling material of the bubble chamber so that short-lived particles such as mesons , heavy baryons or muons are generated and decay. By examining the decay products of a large number of similar decays, further information (e.g. spin and parity ) about the decayed particle can be obtained using a Dalitz diagram , for example .
history
In 1960 Donald A. Glaser received the Nobel Prize in Physics for inventing the bubble chamber in 1952 . Large bubble chambers have been one of the most important particle detectors since the 1960s. At the European nuclear research laboratory CERN , Gargamelle were in operation from 1970 to 1978 and BEBC ( Big European Bubble Chamber ) from 1971 to 1984 . In the meantime, bubble chambers are mostly only used for demonstration purposes, they have become meaningless for modern research facilities. At the Fermilab , however, the suitability of bubble chambers for the search for dark matter in the form of WIMPs is currently being tested as part of the “ Chicagoland Observatory for Underground Particle Physics ” (COUPP) project .
Individual evidence
- ^ Donald A. Glaser: Some Effects of Ionizing Radiation on the Formation of Bubbles in Liquids . In: Physical Review . tape 87 , no. 4 , August 1952, p. 665 , doi : 10.1103 / PhysRev.87.665 (English).
