spark chamber

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spark chamber,

in physics, device for recording the passage of elementary particleselementary particles,
the most basic physical constituents of the universe. Basic Constituents of Matter

Molecules are built up from the atom, which is the basic unit of any chemical element. The atom in turn is made from the proton, neutron, and electron.
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 produced by reactions in a particle acceleratorparticle accelerator,
apparatus used in nuclear physics to produce beams of energetic charged particles and to direct them against various targets. Such machines, popularly called atom smashers, are needed to observe objects as small as the atomic nucleus in studies of its
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. Particles pass through a stack of metal plates or wire grids that are maintained with high voltage between alternate layers. A high-pressure gas fills the gaps between the plates and is ionized along the path of the traversing charged particle. As a result, sparks jump between adjacent, oppositely charged plates and the trail of sparks left by the particle is seen as a series of dashes. The spark chamber has replaced the bubble chamberbubble chamber,
device for detecting charged particles and other radiation by means of tracks of bubbles left in a chamber filled with liquid hydrogen or other liquefied gas. It was invented in 1952 by Donald Glaser.
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 in certain applications. Although the particle paths are recorded more accurately in the bubble chamber, the bubble chamber indiscriminately records all events that occur in a comparatively long interval. The spark chamber operates much more rapidly and can be made highly selective by using auxiliary detectors to screen out unwanted events. Because of its selectivity, the spark chamber is most useful in searching for very rare events. Spark chambers can be highly automated, with data collected and stored electronically instead of photographically, as is necessary with the bubble chamber. The analysis of the data can then be accomplished by a high-speed computer, which may operate simultaneously with the experiment and thereby provide immediate evaluation of the quality of the data and allow optimum operating conditions to be maintained at all times.

spark chamber

A device in which the tracks of charged particles are made visible and their location in space accurately recorded. It consists essentially of a stack of narrowly spaced thin plates or grids in a gaseous atmosphere, partially surrounded by one or more auxiliary particle detectors such as scintillation counters. Any particle detected in one of the auxiliary devices triggers the application of a high-voltage pulse to the stack of plates. The passage of the particle through the plates is then marked by a series of spark discharges along its path. The tracks are recorded by electronic or photographic means. Use of the auxiliary devices leads to a select triggering of the chamber for a particular type of energy or radiation. Spark chambers can be used to detect gamma rays following their conversion to an electron-positron pair.

Spark Chamber

 

a device used for the observation and recording of trajectories (tracks) of charged particles. It is widely used in the study of nuclear particles, nuclear reactions, elementary particles, and cosmic rays.

The simplest type of spark chamber consists of two plane-parallel electrode plates, the space between which is filled with a gas (usually helium, neon, or a mixture). The area of the plates ranges from a few dozen square centimeters to several square meters. Simultaneously with the passage of particles, or with a slight delay (about 1 microsecond [jusec]), a short (10–100 nano-sec) high-voltage potential pulse is fed to the chamber’s electrodes from a pulse generator. A strong electric field (5–20 kilovolts per cm) is created in the working volume of the chamber. The pulse is triggered by a signal from the detector system (scintillation detectors, Cherenkov counters, and so on), which identifies the event being observed. Electrons created along the trajectory of the particle by the ionization of gas atoms are accelerated by the field; they ionize and excite atoms of the gas (collision ionization). As a result, electron-photon avalanches occur along the very short path. Depending on the amplitude and duration of the pulse, these avalanches develop into a visible spark discharge or form localized, glowing regions of small volume in the gas.

A narrow-gap spark chamber, with a distance of about 1 cm between the electrodes, usually consists of a large number of identical spark gaps. Spark discharges propagate perpendicular to the electrodes. A spark chain identifies the direction of the trajectory.

In a track-delineating spark chamber, with a distance of 3–50 cm between the electrodes, spark discharge occurs in the exact direction of the particle trajectory. In this case the electron-photon avalanches developing from primary electrons combine to form a narrow, luminous channel along the track.

In a streamer chamber, which has a distance of about 5–20 cm between the electrodes, avalanches caused by electrons on the track develop individually and are accompanied by localized glowing of the gas. If a short-duration potential pulse (about 10 nanosec) is applied between the electrodes, luminous channels or streamers 3–10 mm long are produced. Such streamers are sufficiently bright to be photographed.

In addition to defining the trajectory, a spark chamber can also in certain cases determine the ionizing power of particles. A spark chamber placed in a magnetic field can be used to determine the momentum of particles from the curvature of their trajectories. Spark chambers can operate with high-intensity particle streams occurring in accelerators, since their memory time (the time over which ionization electrons are preserved in the gas) can be reduced to 1 μsec. On the other hand, spark chambers are capable of very frequent operation, since their dead time, or recovery time, is only a few microseconds.

In addition to photography, methods of recording data from a spark chamber are used that make possible, in particular, the transmission of data from the chamber directly to a computer and the automatic processing of the data. For example, in a wire chamber, where the electrodes consist of a row of thin wires spaced about 1 mm apart, the appearance of a spark is accompanied by a discharge current in the nearest wire. This information makes possible determination of the coordinates of the spark; the data can be transmitted directly to a computer.

In sonic chambers, piezocrystals are installed outside of the gap; they detect the shock wave that forms in the gas at the moment of spark breakdown. The time interval between the appearance of the spark and the signal in a piezocrystal makes it possible to determine the distance between the spark and the crystal (that is, the coordinates of the spark). Here also a direct connection between the piezosensor and a computer is frequently provided.

REFERENCES

Iskrovaia kamera. Moscow, 1967.
Kalashnikova, V. I., and M. S. Kozodaev. Detektory elementarnykh chastits. Moscow, 1966. (Eksperimental’nye metody iadernoi fiziki[part 1].)

M. I. DAION

spark chamber

[′spärk ‚chām·bər]
(nucleonics)
A particle-detecting device in which the trajectory of a charged particle is made visible by a series of sparks that are triggered by the particle as it passes through an array of spark gaps.