Brookhaven 80" Hydrogen Bubble Chamber

Description:

Object EM.N-10118 is the chamber proper of the Brookhaven 80" hydrogen bubble chamber. It is made of Kromarc 55 (a fully anstenitic stainless steel), and has a window (glass) and a neck, surmounted by a piston chamber (stainless steel) and piston (inconel sheet) with an actuator chamber (stainless steel with assorted couplings and tubing.

Basic Principles of Bubble Chambers

Devices for detecting subatomic particles are of two types: “counters” and “chambers.” Counters merely indicate that a particle has passed through (from which signal the energy or velocity of the particle can often also be obtained using two or more such counters separated by a known distance). “Chambers,” however, do not merely signal a transiting particle, but trace its path and—most important—the paths of any other charged particles emerging from collisions which it may undergo with matter filling the chamber.

The first detector of the “chamber” type was the cloud chamber, devised in 1911 by C.T.R. Wilson at the Cavendish Laboratory, Cambridge, England. The tracks of charged particles are rendered visible by the condensation of water vapor about the ionized air molecules (nitrogen and oxygen) produced along the paths of fast-moving charged particles. For an example of a cloud chamber, see object EM.N-08016, Replica of Wilson Cloud Chamber.

Next came the bubble chamber, one of the earliest and most successful imaging detectors. Donald Glaser invented it in the early 1950’s to track particles in high-energy particle collisions. (See object 1980.0356.01, Replica of Glaser’s Six -inch Bubble Chamber.) In April 1953 Berkeley physicist Luis Alvarez met Donald Glaser and learned of his idea and his rudimentary, small, all-glass device. Alvarez was excited by the prospect of a nearly ideal detector for use with the Bevatron particle accelerator, then nearing completion at Berkeley. He immediately turned his assistants and technicians to the problem of developing a liquid-hydrogen bubble chamber. The Berkeley group was the first to demonstrate particle tracks in liquid hydrogen, and then to succeed with a metal-and-glass chamber. The possibility of larger chambers was thus established. (See, for example, objects 1989.0171.04 and 1978.2302.08, Berkeley 4” and 15” Hydrogen Bubble Chambers, respectively.)

The bubble chamber is particularly useful for studying high-energy particles that would pass through a cloud chamber too quickly to leave a detailed enough track, but which pass more slowly through the bubble chamber because of the greater density of the liquid. A typical chamber consists of a sealed container filled with a liquefied gas; and it is designed such that pressure inside can be quickly changed. The idea is to momentarily superheat the fluid when the particles are expected to pass through it. This is accomplished by suddenly lowering the pressure, thereby decreasing the boiling point of the liquefied gas, thus converting it into a superheated liquid. When particles pass through this fluid, they produce dense tracks of localized electron–ion pairs. The energy delivered to the liquid during this process produces tiny bubbles along the particles’ tracks. The tracks of the charged particles can be used to identify the particles, determine their properties, and analyze complex events in which they may be involved.

If an external magnetic field is applied over the volume of the chamber, the tracks of the charged particles will be curved, positively charged particles curving in one direction and negatively charged ones curving in the opposite direction. The degree of curvature depends on the strength of the magnetic field and the particle mass, speed, and charge. Neutral particles (which leave no tracks) can be detected indirectly by applying various conservation laws to the events recorded in the bubble chamber or by observing their decay into pairs of oppositely charged particles. Liquid hydrogen and helium are commonly used in bubble chambers, with cryogenic equipment needed to maintain these gases in their liquid state. For experiments requiring very dense liquids, a variety of organic compounds may be used. Track data are obtained when the chamber is illuminated and photographed by a high-definition camera. The resulting images are then analyzed offline for particle identification and measurement.

Object EM.N-10118, Brookhaven 80-inch bubble chamber, 1963

Objects 1994.3075.01.1 & .01.2, Rear and front parts of model of Brookhaven 80-inch bubble chamber

By the time Berkeley’s 72-inch bubble chamber was completed in 1959, half a dozen other laboratories around the world were planning liquid-hydrogen chambers of that same scale. Among these was Brookhaven National Laboratory, Long Island, New York, whose 30-billion electron-volt Alternating-Gradient Synchrotron (AGS) was to start up in 1960. The 80-inch chamber is surmounted by its expansion cylinder. (Only the ten-ton heart of the original 450-ton apparatus forms object EM.N-10118; the magnet, which accounted for the greatest part of the weight, is not included. The magnet yoke is represented in Objects 1994.3075.01.1 & .01.2, Rear and front parts of model of Brookhaven 80-inch bubble chamber.)

The bubble chamber is made of a non-magnetic stainless steel. A piston in the cylinder above expanded and compressed the liquid hydrogen once per second; it was cycled, and photographed, more than ten million times in the decade it was in operation. The wide thin neck between chamber and cylinder allowed space for the current-carrying copper coils that produced a strong magnetic field throughout the chamber. The stainless steel tubes spraying up on either side served in part to inflate gaskets to seal window to the chamber, but chiefly to pump off any hydrogen that leaked through the seals. The flat glass window, 6 inches thick and weighing 1500 pounds, was, when made, the largest piece of optical quality glass. Behind it the rear inner surface of the chamber is coated with a specially prepared “Scotchlite” material that returns light to within a degree of the direction from which it comes, so as to make the particle tracks clearly visible. The light source and cameras were mounted at the end of a truncated oblong cone (not preserved) that bolted over, and sealed in, the window. Fifty physicists, engineers, and technicians kept the chamber operating 24 hours a day.

The most significant discovery made with Brookhaven’s 80-inch chamber came in the first few months of its operation: the detection of the Ω⁻ particle, whose existence had been predicted by theoretical physicist Murray Gell-Mann. (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 elements in the periodic table.) Beams of K⁻ meson particles, commonly used in studies of the production and interactions of “strange” particles—and particularly in the discovery of the Ω⁻---were obtained by sending the accelerated protons from the AGS crashing into a tungsten target. From the resulting spray of all possible types of particles, a K⁻ beam was formed by eliminating every other particle type with trains of magnets and electrostatic deflectors (“separators”). The beam was directed at the chamber, resulting in collisions between K⁻ mesons and protons. The Ω⁻ particle was detected among the collision particles

These six- and seven-foot bubble chambers of the early 1960s, containing some 200 gallons of liquid hydrogen, were succeeded towards the end of the decade by a generation of 3,000 to 10,000-gallon, barrel-shaped chambers. Of these there were only four; one each at Argonne National Laboratory near Chicago, at Brookhaven National Laboratory, at CERN in Switzerland, and at Fermi National Accelerator Laboratory, also near Chicago. Their leading role in elementary particle physics later passed to complex electronic detectors; see for example object 1977.0708.02, Charpak multiwire proportional chamber.