particle detector

(nucleonics) A device used to indicate the presence of fast-moving charged atomic or nuclear particles by observation of the electrical disturbance created by a particle as it passes through the device. Also known as radiation detector.

A device used to detect and measure radiation characteristically emitted in nuclear processes, including gamma rays or x-rays, lightweight charged particles (electrons or positrons), nuclear constituents (neutrons, protons, and heavier ions), and subnuclear constituents such as mesons. The device is also known as a radiation detector. Since human senses do not respond to these types of radiation, detectors are essential tools for the discovery of radioactive minerals, for all studies of the structure of matter at the atomic, nuclear, and subnuclear levels, and for protection from the effects of radiation. They have also become important practical tools in the analysis of materials using the techniques of neutron activation and x-ray fluorescence analysis. See also Activation analysis; Elementary particle; Nuclear reaction; Nuclear spectra; Particle accelerator; Prospecting; Radioactivity; X-ray fluorescence analysis.

A convenient way to classify radiation detectors is according to their mode of use: (1) For detailed observation of individual photons or particles, a pulse detector is used to convert each such event (that is, photon or particle) into an electrical signal. (2) To measure the average rate of events, a mean-current detector, such as an ion chamber, is often used. Radiation monitoring and neutron flux measurements in reactors generally fall in this category. Sometimes, when the total number of events in a known time is to be determined, an integrating version of this detector is used. (3) Position-sensitive detectors are used to provide information on the location of particles or photons in the plane of the detector. (4) Track-imaging detectors image the whole three-dimensional structure of a particle's track. The output may be recorded by immediate electrical readout or by photographing tracks as in the bubble chamber. (5) The time when a particle passes through a detector or a photon interacts in it is measured by a timing detector. Such information is used to determine the velocity of particles and when observing the time relationship between events in more than one detector.

The ionization produced by a charged particle is the effect commonly employed in a particle detector. In the basic type of gas ionization detector, an electric field applied between two electrodes separates and collects the electrons and positive ions produced in the gas by the radiation to be measured. Multiwire proportional chambers and spark chambers are position-sensitive adaptations of gas detectors. The signal division or time delay that occurs between the ends of an electrode made of resistive material is sometimes used to provide position sensitivity in gas and semiconductor detectors. Track-imaging detectors rely on a secondary effect of the ionization along a particle's track to reveal its structure. See also Ionization chamber.

In a semiconductor detector, a solid replaces the gas. The “insulating” region (depletion layer) of a reverse-biased pn junction in a semiconductor is employed. Since solids are approximately 1000 times denser than gases, absorption of radiation can be accomplished in relatively small volumes. A less obvious but fundamental advantage of semiconductor detectors is the fact that much less energy is required (∼3 eV) to produce a hole-electron pair than that required (∼30 eV) to produce an ion electron pair in gases. See also Crystal counter; Junction detector.

In addition to producing free electrons and ions, the passage of a charged particle through matter temporarily raises electrons in the material into excited states. When these electrons fall back into their normal state, light may be emitted and detected as in the scintillation detector. See also Scintillation counter.

Neutral particles, such as neutrons, cannot be detected directly by ionization. Consequently, they must be converted into charged particles by a suitable process and then observed by detecting the ionization caused by these particles.

Although ionization detectors dominate the field, a number of detector types based on other radiation-induced effects are used. Examples are (1) transition radiation detectors, which depend on the x-rays and light emitted when a particle passes through the interface between two media of different refractive indices; (2) track detectors, in which the damage caused by charged particles in plastic films and in minerals is revealed by etching procedures; (3) thermoluminescent and radiophotoluminescent detectors, which rely on the latent effects of radiation in creating traps in a material or in creating trapped charge; and (4) Cerenkov detectors, which depend on measurement of the light produced by passage of a particle whose velocity is greater than the velocity of light in the detector medium. See also Cerenkov radiation; Particle track etching; Transition radiation detectors.

The very large detector systems used in relativistic heavy-ion experiments and in the detection of the products of collisions of charged particles at very high energies, typically at the intersection region of storage rings, deserve special consideration. These detectors are frequently composites of several of the basic types of detectors discussed above and are designed to provide a detailed picture of the multiple products of collisions at high energies. The complete detector system may occupy a space tens of feet in extent and involve tens or hundreds of thousands of individual signal processing channels, together with large computer recording and analysis facilities.

Any device for converting radiant energy to a form more suitable for observation and recording. Examples include x-ray films and radiometers.

The Compact Muon Solenoid (CMS) is an example of a large particle detector. Notice the person for scale.

In experimental and applied particle physics and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify high-energy particles, such as those produced by nuclear decay, cosmic radiation, or reactions in a particle accelerator. Modern detectors are also used as calorimeters to measure the energy of the detected radiation. They may also be used to measure other attributes such as momentum, spin, charge etc. of the particles.

Contents 1 Description 1.1 Examples and types 1.2 Modern detectors 2 Installations of particle detectors 2.1 At colliders 2.2 Under construction 2.3 Without colliders 3 See also 4 External articles and references

Description

Summary of Particle Detectors

Detectors designed for modern accelerators are huge, both in size and in cost. The term counter is often used instead of detector, when the detector counts the particles but does not resolve its energy or ionization. Particle detectors usually can also track ionizing radiation (high energy photons or even visible light). If their main purpose is radiation measurement, they are called radiation detectors, but as photons are also (massless) particles, the term particle detector is still correct.

Examples and types

Many of the detectors invented and used so far are ionization detectors (of which gaseous ionization detectors and semiconductor detectors are most typical) and scintillation detectors; but other, completely different principles have also been applied, like Čerenkov light and transition radiation.

Cloud chamber with visible tracks from ionizing radiation (short, thick: α-particles; long, thin: β-particles

Historical Examples

• Bubble chamber
• Wilson cloud chamber (diffusion chamber)
• Photographic plates

Detectors for Radiation Protection

• Dosimeter
• Electroscope (miniature electroscopes are used as portable dosimeters)

Commonly used detectors for Particle and Nuclear Physics

• Gaseous ionization detectors
  • Ionization chamber
  • Proportional counter
    • Multiwire Proportional Chamber
    • Drift chamber
    • Time projection chamber
  • Geiger-Müller tube
  • Spark chamber

• Solid-state detectors
  • Cherenkov detector
    • RICH (Ring Imaging Cherenkov Detector)
  • Scintillation counter and associated Photomultiplier or Photodiode / Avalanche photodiode
    • Lucas cell
    • Time of flight detector
  • Semiconductor detector
    • Silicon Vertex Detector
  • Transition radiation detector

• Calorimeters

Modern detectors

Main article: Hermetic detector

Modern detectors in particle physics combine several of the above elements in layers much like an onion.

Installations of particle detectors

At colliders

• At CERN
  • for the LHC
    • CMS
    • ATLAS
    • ALICE
    • LHCb
  • for the LEP
    • Aleph[1]
    • Delphi[2]
    • L3
    • Opal[3]
  • for the SPS
    • The COMPASS Experiment
    • Gargamelle
    • NA49
• At Fermilab
  • for the Tevatron
    • CDF
    • D0
• At DESY
  • for HERA
    • H1
    • HERA-B
    • HERMES
    • ZEUS
• At BNL
  • for the RHIC
    • PHENIX
    • Phobos (physics)
    • STAR
• At SLAC
  • for the PeP-II
    • BaBar
  • for the SLC
    • SLD
• At Cornell
  • for CESR
    • CLEO
    • CUSB
• Others
  • MECO from UC Irvine

Under construction

• For ILC
  • CALICE

Without colliders

• Super-Kamiokande
• AMANDA
• CMDS

See also

• List of particles

External articles and references

Filmstrips

• "Radiation detectors". H. M. Stone Productions, Schloat. Tarrytown, N.Y., Prentice-Hall Media, 1972.

General Information

• The Particle Detector BriefBook
• How to Build a Cloud Chamber
• Grupen, C. (June 28-July 10 1999). "Physics of Particle Detection". AIP Conference Proceedings, Instrumentation in Elementary Particle Physics, VIII. 536. Istanbul: Dordrecht, D. Reidel Publishing Co.. pp. 3–34. doi:10.1063/1.1361756. 

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)