Larry Bennett, age 15, of Las Vegas, Nev., for his question:
WHAT IS A SPARK CHAMBER?
A spark chamber is a device which makes visible the paths followed by electrically charged atomic particles. Spark chambers are used by nuclear physicists to study these particles, which are too small and travel too fast to be seen by the naked eye.
The first practical spark chamber was built in 1959 by two Japanese physicists, S. Fukui and S. Miyamoto. Since 1960, the spark chamber has become an important research tool for high energy nuclear physicists.
Physicists use the spark chamber with similar devices called the Wilson cloud chamber and the bubble chamber. But unlike these devices, the spark chamber can be made sensitive for just the short interval that a particle a physicist wants to study is in the chamber.
A spark chamber is made of a series of thin metal plates set parallel in an airtight box that is filled with neon gas. A gap of from three to 400 millimeters separates the plates, depending upon the design of the chamber.
A typical spark chamber is about three feet long and has 150 plates spaced six millimeters apart. Electrical equipment powers the chamber.
The spark chamber is often used with a device called a particle accelerator. This device produces high energy particles that can be studied in the cahmber.
When a charged atomic particle enters the chamber, it ionizes or electrically charges the neon gas atoms in its path. The particle penetrates the thin metal plates. The ionized gas atoms will conduct electricity, but the atoms that have not ionized will not. An electrical field of 1,000 volts per millimeter of plate separation is applied to alternate plates immediately after the particle ionizes the neon. This field causes a lightning like spark to jump from plate to plate along the particles ionized path.
The spark can easily be seen and photographed by the physicist.
Special electronic circuits apply the high voltage to the plates after a selected particle enters the chamber. Physicists can select the particle they wish to study in the chamber. By eliminating unwanted particle tracks or paths, the physicist can spend more time studying the important tracks.
Physicists learn much about the nucleus of the atom and atomic particles by studying the tracks made by such particles. They have discovered several previously unknown particles with the help of spark chambers.
During the late 1960s and the 1970s, physicists developed two devices similar to the spark chamber, the magnetostrictive chamber and the proportional wire chamber. The construction of both these devices closely resembles that of the spark chamber, but wires are used instead of metal plates.
As particles pass through the airtight box of each device, they create electric impulses on the wires. These impulses are read by a computer to determine the paths taken by the particles. Physicists find the proportional wire chamber particularly useful because it can make separate measurement of many more particles per second than a spark chamber can.