The bubble chamber, invented by Donald Glaser in 1952, is a device used in physics to detect charged particles by creating a trail of bubbles that can be photographed. While it was once prevalent, it is now rarely used due to drawbacks with high-energy particles. However, bubble chamber images are still useful for educational purposes.
A bubble chamber is a device used in physics to detect charged particles. It was invented by Donald Glaser in 1952 and was later awarded the Nobel Prize for his invention. While it was once the prevalent way to detect particles, the bubble chamber is currently not used as frequently, largely due to some drawbacks that arise when dealing with very high-energy particles.
The principle behind the bubble chamber, and indeed most particle detectors, is quite simple. It can be thought of as watching the sky for tracks left by airplanes. Even if a jet passes so fast that you don’t notice it passing, you will see its trail for a while, allowing you to reconstruct the path it took. A bubble chamber works on a similar principle, with particles leaving a trail of bubbles that can be photographed.
The chamber itself is filled with some sort of clear, unstable liquid, often superheated hydrogen. The liquid is heated by holding it under pressure and releasing it slightly when the particles are introduced. As charged particles make their way through the chamber, they boil the liquid as they pass, creating a trail of bubbles. The particles themselves take only a few nanoseconds to pass through the chamber, but the bubbles take millions of times longer to expand, generally taking around 10ms. At that moment, photographs can be taken from various angles, creating a three-dimensional representation of the path of the particles.
The bubbles are then eliminated by pressurizing the chamber and the procedure is repeated with the next batch of particles. Each series of photographs is taken over what we might consider a short period of time, taking only a few seconds each, but is actually quite long by scientific standards. Modern detectors are capable of performing the entire procedure in milliseconds, allowing hundreds or thousands of particle bursts to be documented in seconds. Modern detectors also capture images digitally, making them easier to analyze and archive.
As a result, the bubble chamber is rarely used in modern particle detection. Another problem is that because bubble chambers are quite small, they are also incapable of adequately documenting collisions of high-energy particles, further reducing their usefulness in modern experiments. Finally, the point at which the liquid heats up must coincide exactly with the moment the instantaneous particles meet, which can be nearly impossible to coordinate with particles that have extremely short lifetimes.
Despite their relative obsolescence, bubble chamber images are still very useful for educational purposes. Because they are photographs of physical traces, they are generally much easier for people to understand than more complex descriptions of interactions or other abstract data. Students can look at a captured image of a trail of bubbles and see precisely the interactions of various particles and how the particles decay during their time in the chamber. For these reasons, while not used much in cutting-edge research, bubble chambers still see some use in university laboratories, and historically taken photographs are often found in textbooks.
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