80-inch Bubble Chamber

The subatomic particles produced in an accelerator are so minute that they cannot be seen. But physicists can still "look" at them and learn about their properties by causing collisions to occur within a detector that can record these events in some way.

At the Cosmotron, most collisions took place in detectors called "cloud chambers", devices filled with supersaturated gases. Particles darting through the gas cloud collided with gas atoms, briefly leaving a trail of small, clearly visible droplets. These tracks could be photographed and analyzed. However, this early detector technology was limited.

To see more events of interest, researchers developed a technique that used a liquid target instead of a gas. If the liquid were kept at extremely cold temperatures, then charged particles flying through it would leave a visible trail of bubbles along their path. Because liquids are denser than gases, many more events would occur in such a device. It would also be possible to track more desirable secondary particles along longer flight paths. Thus, the bubble chamber made cloud chambers obsolete. 

In 1959, Brookhaven scientists and engineers began design work on a very large bubble chamber, about 80 inches long, for use at the Alternating Gradient Synchrotron (AGS). The chamber would be filled with 240 gallons of super-cold liquid hydrogen, surrounded by a 31-ton magnet. The magnet would be used to create a field which would deflect various charged particles along different paths, providing information on their momentum, mass, and other key details.

The machine itself was a marvel of mechanical engineering. The volume of the chamber was rapidly expanded by moving a 250-pound piston a mere half of an inch in 0.015 seconds, dropping the chamber pressure enough to make the hydrogen sensitive to the microscopic heat spikes caused by passing particles. The bubble tracks formed would be photographed by cameras which looked into the chamber through a 1,500 pound, polished glass window--the largest piece of lens-quality glass ever cast. The chamber was then recompressed by the piston, readying the detector for another round of photography. This whole cycle was completed in only 0.03 seconds!

One drawback of this detector technology was that a staff of trained analysts had to examine thousands of chamber photographs manually, searching for that one special event that researchers were looking for--by looking at up to 250,000 pictures per month.

The omega-minus particle

When the first photograph of particle interactions was made in June 1963, the 80-inch Bubble Chamber was the largest such detector in the world. The most famous discovery made at this detector was by a team of researchers led by future Laboratory director Nicholas Samios. In 1964, this team established the existence of the omega-minus particle, which was previously only theorized to exist. This finding supported the first attempt by physicists to organize the increasingly long list of subatomic particles into an orderly pattern, similar to that used to arrange chemicals in the periodic table.

The 80-inch detector was eventually decommissioned in 1974. By that time, it had been superceded by Brookhaven's then newest particle detector, the 7-Foot Bubble Chamber.

A detailed explanation of the workings of the 80-inch chamber can be found in BNL publication 9065, available here as a 1.3 MB PDF file. This is a general interest booklet which was published in 1966.

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

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