Townsend avalanche

Townsend avalanche

A Townsend avalanche is a cascade reaction involving electrons in a region with a sufficiently high electric field. This reaction must also occur in a medium that can be ionized, such as air. It is exploited in devices such as Geiger counters and Proportional counters to detect and measure the energy of an ionizing radiation. Incoming radiation ionizes one of the atoms or molecules in the medium. The positive ion drifts towards the cathode, while the free electron drifts towards the anode of the particular device. It accelerates in the electric field, gaining sufficient energy such that it frees another electron upon collision with another atom/molecule of the medium. The two free electrons then travel together some distance before another collision occurs. The number of electrons travelling towards the anode is multiplied by a factor of two for each collision, so that after "n" collisions, there are 2n free electrons.

When the electrons reach the anode, a current is induced, which is amplified further with electronics. This gives a clear signal that allows humans one way to detect and measure some of the characteristics of the incident ionizing radiation.

See Also

* Townsend discharge


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  • Townsend avalanche — Taunsendo griūtis statusas T sritis fizika atitikmenys: angl. Townsend avalanche vok. Townsend Lawine, f; Townsendsche Lawine, f rus. лавина Таунсенда, f; таунсендовская лавина, f pranc. avalanche de Townsend, f …   Fizikos terminų žodynas

  • Townsend avalanche breakdown — Taunsendo griūtinis pramušimas statusas T sritis fizika atitikmenys: angl. Townsend avalanche breakdown vok. Townsendscher Lawinendurchschlag, m rus. лавинный пробой Таунсенда, m pranc. claquage par avalanche de Townsend, m …   Fizikos terminų žodynas

  • Townsend avalanche — noun see avalanche I * * * /town zeuhnd/, Physics. avalanche (def. 3). [named after J. S. E. Townsend (1868 1957), Irish physicist] …   Useful english dictionary

  • Townsend avalanche — /town zeuhnd/, Physics. avalanche (def. 3). [named after J. S. E. Townsend (1868 1957), Irish physicist] * * * …   Universalium

  • Townsend — is a surname of Yorkshire and Norfolk origin. In English its meaning is a topographic name indicating residence at the extremity of a city or burgh (from Middle English touun ‘village’, ‘hamlet’, ‘stead’ + ende ‘end’.) The name is first… …   Wikipedia

  • avalanche de Townsend — Taunsendo griūtis statusas T sritis fizika atitikmenys: angl. Townsend avalanche vok. Townsend Lawine, f; Townsendsche Lawine, f rus. лавина Таунсенда, f; таунсендовская лавина, f pranc. avalanche de Townsend, f …   Fizikos terminų žodynas

  • avalanche — /av euh lanch , lahnch /, n., v., avalanched, avalanching. n. 1. a large mass of snow, ice, etc., detached from a mountain slope and sliding or falling suddenly downward. 2. anything like an avalanche in suddenness and overwhelming quantity: an… …   Universalium

  • Townsend-Lawine — Taunsendo griūtis statusas T sritis fizika atitikmenys: angl. Townsend avalanche vok. Townsend Lawine, f; Townsendsche Lawine, f rus. лавина Таунсенда, f; таунсендовская лавина, f pranc. avalanche de Townsend, f …   Fizikos terminų žodynas

  • Townsend coefficient — The first Townsend coefficient ( α ), also known as first Townsend avalanche coefficient is a term used in an ionization process where there is a possibility of secondary ionization because the primary ionization electrons gain sufficient energy… …   Wikipedia

  • Townsend ionization — avalanche i …   Medical dictionary

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