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Posts Tagged ‘Bubble chambers’

A stroll down memory lane!

Tuesday, October 6th, 2009

I recently read an article by Nick and Lizzie that described the “weird” architecture at Fermilab. It mentioned the 15 foot bubble chamber, a detector of yore that has now been turned into the “world’s strangest lawn ornament”. I did my thesis work on an experiment that used this detector; I am probably one of the last students to have worked on a large bubble chamber experiment.

Before the advent of high speed electronics and powerful computers, bubble chambers were the detectors of choice. Many crucial discoveries were made with them, e.g., the discovery of the Omega- particle at BNL, which set the foundation for theories based on quarks, discovery of Neutral currents at CERN, which confirmed the validity of Glashow-Weinberg-Salam model of electro-weak unification, not to mention the plethora of particles found in the late 50’s and 60’s at Berkeley.

“A bubble chamber is a vessel filled with a superheated transparent liquid (most often liquid hydrogen) used to detect electrically charged particles moving through it.” You basically shot a beam of particles at the chamber, which would interact with the protons/neutrons in the target liquid. Just as the beam arrived, you would compress “expand” the liquid with a piston (see Kenneth’s comment below); this would cause the liquid to become superheated, and as charged particles moved through the liquid, they would cause local boiling that would show up as bubbles. We took photographs of these “bubbly” tracks, which were scanned (by humans) on specially designed tables that used precise instruments to measure the trajectory of various particles, thus obtaining their momentum. The data was then fed into computers. From this point on, analysis was similar to that on modern detectors, e.g., ATLAS. There was an “army” of scanners who measured the events.

Here are some pictures taken in bubble chambers. In the left panel of Figure 1, you can see the actual photograph of the “famous” Omega- event, and in the right panel you can see an annotated version (you can see much better if you print out the photograph and look at it edge-wise); you should also read the description in the caption. This experiment used a kaon beam.

Figure 1. The discovery of the Omega-

Figure 1. The discovery of the Omega-

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