Gaseous ionization detectors
Encyclopedia
In particle physics
, gaseous ionization detectors are detectors designed to seek the presence of particles (a particle detector
). If a particle has enough energy to ion
ize a gas
atom or molecule, the resulting electron
s and ion
s cause a current flow which can be measured in different ways. The three basic types of gaseous ionization detectors are:
All of these have the same basic design of two electrode
s separated by air or a special counting gas, but each uses a unique method to form the total number of ion-pairs that are collected. The strength of the electric field
between the electrodes determines the detector's response to ionizing radiation
.
Ionization chamber
s operate at a low voltage, selected such that no avalanche multiplication takes place. Current is generated by the drift of ions to anode or cathode.
Proportional counter
s operate at a slightly higher voltage, selected such that limited avalanche multiplication takes place. The avalanche is localised, rather than spreading widely through the detecting gas, so that an output current pulse is generated which is proportional to the detected particle energy. The term "gas proportional detector" (GPD) is generally used in radiometric practice, and the property of being able to detect particle energy is particular useful when using flat arrays for Alpha and Beta particle detection and discrimination.
Geiger-Müller tube
s are the primary components of Geiger counters. They operate at an even higher voltage, selected such that avalanche multiplication is total, and the entire gas volume ionizes from a single event. The peak in current is passed through an audio device producing the clicks of the Geiger Mueller counter.
Wire chamber
s are essentially gaseous ionization detectors with many electrodes instead of one.
Ionization-type smoke detector
s are gaseous ionization detectors. A bit of radioactive americium
is placed so that it maintains a current between the two plates. If smoke gets between the plates where the ionization is taking place, the ionized gas can be neutralized leading to a reduced current. The decrease in current triggers a fire alarm.
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
, gaseous ionization detectors are detectors designed to seek the presence of particles (a particle detector
Particle detector
In experimental and applied particle physics, nuclear 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...
). If a particle has enough energy to ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
ize a gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
atom or molecule, the resulting electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s and ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s cause a current flow which can be measured in different ways. The three basic types of gaseous ionization detectors are:
- ionization chamberIonization chamberThe ionization chamber is the simplest of all gas-filled radiation detectors, and is used for the detection or measurement of ionizing radiation...
s - proportional counterProportional counterA proportional counter is a measurement device to count particles of ionizing radiation and measure their energy.A proportional counter is a type of gaseous ionization detector. Its operation is similar to that of a Geiger-Müller counter, but uses a lower operating voltage. An inert gas is used to...
s - Geiger-Müller tubeGeiger-Müller tubeA Geiger–Müller tube is the sensing element of a Geiger counter instrument that can detect a single particle of ionizing radiation, and typically produce an audible click for each. It was named for Hans Geiger who invented the device in 1908, and Walther Müller who collaborated with Geiger in...
s
All of these have the same basic design of two electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
s separated by air or a special counting gas, but each uses a unique method to form the total number of ion-pairs that are collected. The strength of the electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
between the electrodes determines the detector's response to ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
.
Ionization chamber
Ionization chamber
The ionization chamber is the simplest of all gas-filled radiation detectors, and is used for the detection or measurement of ionizing radiation...
s operate at a low voltage, selected such that no avalanche multiplication takes place. Current is generated by the drift of ions to anode or cathode.
Proportional counter
Proportional counter
A proportional counter is a measurement device to count particles of ionizing radiation and measure their energy.A proportional counter is a type of gaseous ionization detector. Its operation is similar to that of a Geiger-Müller counter, but uses a lower operating voltage. An inert gas is used to...
s operate at a slightly higher voltage, selected such that limited avalanche multiplication takes place. The avalanche is localised, rather than spreading widely through the detecting gas, so that an output current pulse is generated which is proportional to the detected particle energy. The term "gas proportional detector" (GPD) is generally used in radiometric practice, and the property of being able to detect particle energy is particular useful when using flat arrays for Alpha and Beta particle detection and discrimination.
Geiger-Müller tube
Geiger-Müller tube
A Geiger–Müller tube is the sensing element of a Geiger counter instrument that can detect a single particle of ionizing radiation, and typically produce an audible click for each. It was named for Hans Geiger who invented the device in 1908, and Walther Müller who collaborated with Geiger in...
s are the primary components of Geiger counters. They operate at an even higher voltage, selected such that avalanche multiplication is total, and the entire gas volume ionizes from a single event. The peak in current is passed through an audio device producing the clicks of the Geiger Mueller counter.
Wire chamber
Wire chamber
A multi-wire chamber is a detector for particles of ionizing radiation which is an advancement of the concept of the Geiger counter and the proportional counter....
s are essentially gaseous ionization detectors with many electrodes instead of one.
Ionization-type smoke detector
Smoke detector
A smoke detector is a device that detects smoke, typically as an indicator of fire. Commercial, industrial, and mass residential devices issue a signal to a fire alarm system, while household detectors, known as smoke alarms, generally issue a local audible and/or visual alarm from the detector...
s are gaseous ionization detectors. A bit of radioactive americium
Americium
Americium is a synthetic element that has the symbol Am and atomic number 95. This transuranic element of the actinide series is located in the periodic table below the lanthanide element europium, and thus by analogy was named after another continent, America.Americium was first produced in 1944...
is placed so that it maintains a current between the two plates. If smoke gets between the plates where the ionization is taking place, the ionized gas can be neutralized leading to a reduced current. The decrease in current triggers a fire alarm.