An ionization chamber is a device used for two major purposes: detecting particles in air (as in a smoke detector), and for detection or measurement of ionizing radiation. A smoke detector is a device that detects Smoke and issues an Alarm. Image talkNew_radiation_symbol_ISO_21482svg for details --> Ionizing radiation
An ionization chamber is an instrument constructed to measure the number of ions within a medium (which we will consider to be gaseous, but can also be solid or liquid). An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge It consists of a gas filled enclosure between two conducting electrodes. An electrode is an Electrical conductor used to make contact with a nonmetallic part of a circuit (e The electrodes may be in the form of parallel plates or coaxial cylinders to form a convenient portable detector in which case, one of the electrodes may be the wall of the vessel itself.
When gas between the electrodes is ionized by any means, such as by alpha particles, beta particles, X-rays, or other radioactive emission, the ions and dissociated electrons move to the electrodes of the opposite polarity, thus creating an ionization current which may be measured by a galvanometer or electrometer. Alpha particles (named after and denoted by the first letter in the Greek alphabet, α consist of two Protons and two Neutrons bound together into a Beta particles are high-energy high-speed Electrons or Positrons emitted by certain types of Radioactive nuclei such as Potassium -40 X-radiation (composed of X-rays) is a form of Electromagnetic radiation. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. A galvanometer is a type of Ammeter; an instrument for detecting and measuring Electric current. An electrometer is an electrical instrument for measuring Electric charge or electrical Potential difference.
Each ion essentially deposits or removes a small electric charge to or from an electrode, such that the accumulated charge is proportional to the number of like-charged ions. A voltage potential that can range from a few volts to many kilovolts is applied between the electrodes, and allows the device to work continuously by mopping up electrons and preventing the device from becoming saturated. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The current that originates is called a bias current, and prevents the device from reaching a point where no more ions can be collected. Biasing in Electronics is the method of establishing predetermined Voltages and/or Currents at various points of a circuit to set an appropriate
Ionization chambers are widely used in the nuclear industry since they provide an output that is proportional to dose and have a greater operating lifetime than standard Geiger tubes (in Geiger tubes (cf. Geiger-Müller tube) the gas eventually breaks down). A Geiger-Müller tube (or GM tube) is the sensing element of a Geiger counter instrument that can detect a single particle of Ionizing radiation, and typically Ionization chambers are used in nuclear medicine to determine the exact activity of radioactive therapeutic treatments. Such devices are called 'radioisotope dose calibrators'. Ion chambers are sometimes microphonic since they are very sensitive devices and non ion related charges can be set up inside due to the piezoelectric effect. Microphonics describes the phenomenon where certain components in electronic devices transform mechanical Vibrations into an undesired electrical signal ( Piezoelectricity is the ability of some materials (notably Crystals and certain Ceramics including bone to generate an Electric potential in response to
Radiation detectors
A Geiger-Müller tube—used in a Geiger counter—is another type of ionization chamber. A Geiger counter, also called a Geiger-Müller counter, is a type of Particle detector that measures Ionizing radiation. In such a tube, one plate is wrapped into a cylinder. In place of the other plate is a wire placed along the cylindrical plate's axis. This type of tube is usually sealed and filled with an inert gas. In this device, no current normally flows between the two electrodes even though they are held at different potentials.
If a particle of ionizing radiation enters the tube (an alpha particle, a beta particle, or a gamma ray) it may ionize an atom within the tube. Alpha particles (named after and denoted by the first letter in the Greek alphabet, α consist of two Protons and two Neutrons bound together into a Beta particles are high-energy high-speed Electrons or Positrons emitted by certain types of Radioactive nuclei such as Potassium -40 Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions The rapid acceleration of the resulting electron by the electrostatic potential within the tube may result in a Townsend avalanche, or a cascade of electrons from further ionization events. A Townsend avalanche is a cascade reaction involving Electrons in a region with a sufficiently high Electric field. The electrons and ions created by the avalanche then migrate to the electrodes within the Geiger counter inducing a brief pulse of current. If this output is connected to headphones, one hears the familiar staccato pops of a Geiger counter. In Musical notation, the Italian word staccato (literally detached, plural staccatos or staccati) indicates that notes
Many different types of radiation counters and detectors are based on Geiger-Müller tube-like devices. Some contain different fill gases; some are filled with liquids; some are open to air. For example, a bubble chamber contains a liquid under pressure just below its boiling point. A bubble chamber is a vessel filled with a superheated transparent Liquid (most often Liquid hydrogen) used to detect electrically charged Different measurements are possible depending on the type of window in the device (a glass window will not pass alpha particles, while a mica window will) or the potential difference between the electrodes.
With the development of cosmic ray physics and nuclear physics it became desirable to alter the simple Geiger counter, an "all or nothing" proposition, so as to discriminate among incident ionizing particles according to the energy. For the 1962 Bruce Conner film see Cosmic Ray (film Cosmic rays are energetic particles originating from space that impinge on Nuclear physics is the field of Physics that studies the building blocks and interactions of Atomic nuclei. A Geiger counter, also called a Geiger-Müller counter, is a type of Particle detector that measures Ionizing radiation. The less sophisticated detector that resulted is the proportional counter. A proportional counter is a measurement device to count particles of Ionizing radiation and measure their Energy.
Smoke detectors
In a smoke detector, the gap between the plates is exposed to open air. A smoke detector is a device that detects Smoke and issues an Alarm. The chamber contains a small amount of americium-241, which is an emitter of alpha particles. Americium (ˌæməˈrɪsiəm is a Synthetic element that has the symbol Am and Atomic number 95 Alpha particles (named after and denoted by the first letter in the Greek alphabet, α consist of two Protons and two Neutrons bound together into a These alpha particles carry a substantial amount of energy, and when they collide with gas in the ionization chamber (mostly nitrogen and oxygen) the momentum transferred can ionize the gas molecules—that is, the uncharged gas molecules will lose one or more electrons and become charged ions. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge
Since the plates are at different voltages (in a typical smoke detector, the voltage difference is a few volts) the ions and electrons will be attracted to the plates. This small flow of ions between the plates represents a measurable electric current. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. If smoke enters the detector, it disrupts this current. Smoke is the collection of airborne solid and liquid Particulates and Gases ref> ''Smoke Production and Properties'' - SFPE Handbook of Fire Protection Engineering Ions strike smoke particles and are neutralized. This drop in current triggers the alarm.
Radiation measurement
In medical physics and radiotherapy, ionization chambers are used to ensure that the dose delivered from a therapy unit or radiopharmaceutical is that intended. Medical physics is the application of Physics to Medicine. It generally concerns physics as applied to Medical imaging and Radiotherapy, although Radiation therapy (or radiotherapy) is the medical use of Ionizing radiation as part of Cancer treatment to control Malignant Ionization chambers are connected to electrometers and typically report a collected charge in nanocoulombs. A factor is then required to convert this reading into a meaningful dose. Often a chamber will have a factor established by a national standards laboratory such as the NPL in the UK, or will have a factor determined by comparison against a standards-calibrated chamber at the user's site.
See dosimetry. Radiation dosimetry is the calculation of the Absorbed dose in matter and tissue resulting from the exposure to Ionizing radiation.
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