Nuklearna fisija – razlika između verzija

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=== Mehanizam ===
[[Image:UFission.gif|250px300px|right|thumb|Vizuelna reprezentacija događaja indukovanjeindukovanja nuklearne fuzije, upri komečemu se sporo krećući neutron apsporbuje u jezgru atoma uranijuma-235, usled čega dolazi do fisije u dva lakša elementa (fisiona produkta) koji se brzo kreću i u dodatne neutrone. Najveći deo oslobođene energije je u obliku kinetičke brzine fisionih produkata i neutrona.]]
[[Image:ThermalFissionYield.svg|thumb|300px|FisioniPrinosi productfisionih yieldsprodukata bypo massmasi forza [[thermaltermalni neutron|termalnu neutronsku]] fission offisiju [[UraniumUranijum-235|U-235]], [[Pu-239]], akombinaciju combinationkoja ofje thetipična twoza typicaldanašnje ofnuklearne current nuclear power reactorsreaktore, andi [[UraniumUranijum-233|U-233]] usedkoji inse thekoristi u [[thoriumtorijumski ciklus|torijumskom cycleciklusu]].]]
 
Nuklearna fisija se može odvijati bez [[neutron]]skog bombardovanja, kao tip [[radioaktivni raspad|radioaktivnog raspada]]. Ovaj tip fisije (takazvana [[spontana fisija]]) je redak izuzev u slučaju nekoliko teških izotopa. U nuklearnim uređajima, esencijalno sva nuklearna fisija se odvija kao "[[nuklearna reakcija]]" — bombardovanjem vođeni proces koji proizilazi iz kolizije dve subatomske čestice. U nuklearnim reakcijama, subatomska čestica se sudara sa atomskim jezgrom i uzrokuje promene u njemu. Nuklearne reakcije su stoga vođene mehanikom bombardovanja, ne samo relativno konstantnim [[eksponencijalni raspad|eksponencijalnim raspadom]] i [[polu-život]]om karakterističnim za spontane radioaktivne procese.
Nuklearna fisija can occur without [[neutron]] bombardment as a type of [[radioactive decay]]. This type of fission (called [[spontaneous fission]]) is rare except in a few heavy isotopes. In engineered nuclear devices, essentially all nuclear fission occurs as a "[[nuclear reaction]]" — a bombardment-driven process that results from the collision of two subatomic particles. In nuclear reactions, a subatomic particle collides with an atomic nucleus and causes changes to it. Nuclear reactions are thus driven by the mechanics of bombardment, not by the relatively constant [[exponential decay]] and [[half-life]] characteristic of spontaneous radioactive processes.
 
Mnogi tipovi [[nuklearna reakcija|nuklearnih reakcija]] su poznati. Nuklearna fisija se značajno razlikuje od drugih tipova nuklearnih reakcija, po tome da ona može da bude pojačana i ponekad kontrolisana [[nuklearna lančana reakcija|nuklearne lančane reakcije]] (jednog tipa opšte [[lančana reakcija|lančane reakcije]]). U takvoj reakciji, slobodni [[neutron]]i oslobođeni fisijom mogu da izazovu dodatne reakcije fisije, čime se zatim oslobađa još više neutrona i uzrokuje dalja fisija.
Many types of [[nuclear reactions]] are currently known. Nuclear fission differs importantly from other types of nuclear reactions, in that it can be amplified and sometimes controlled via a [[nuclear chain reaction]] (one type of general [[chain reaction]]). In such a reaction, free [[neutrons]] released by each fission event can trigger yet more events, which in turn release more neutrons and cause more fissions.
 
The [[chemical elementIzotopi]] [[isotopeshemijski element|hemijskih elemenata]] thatkoji canmogu sustainda apodržavaju fissionfisionu chainlančanu reactionreakciju arese callednazivaju [[nuclearnuklearno fuelgorivo|nuklearna goriva]]s, andi arekaže saidse toda besu ''[[fissile]]fisivi''. The mostNajčešće commonkorišćena nuclearnuklearna fuelsgoriva aresu [[uraniumuranijum-235|<sup>235</sup>U]] (the isotope ofizotop [[uraniumuranijum]]a with ansa [[atomicatomska masa|atomskom massmasom]] ofod 235 andi of use in nuclear reactors) and [[Plutonium-239|<sup>239</sup>Pu]] (the isotope of [[plutonium]] with an [[atomic mass]] of 239). These fuels break apart into a bimodal range of chemical elements with atomic masses centering near 95 and 135&nbsp;'''u''' ([[fission products]]). Most nuclear fuels undergo [[spontaneous fission]] only very slowly, decaying instead mainly via an [[alpha particle|alpha]]/[[beta particle|beta]] [[decay chain]] over periods of [[millennium|millennia]] to [[Eon (geology)|eons]]. In a [[nuclear reactor]] or nuclear weapon, the overwhelming majority of fission events are induced by bombardment with another particle, a neutron, which is itself produced by prior fission events.
 
Nuclear fissions in fissile fuels are the result of the nuclear excitation energy produced when a fissile nucleus captures a neutron. This energy, resulting from the neutron capture, is a result of the attractive [[nuclear force]] acting between the neutron and nucleus. It is enough to deform the nucleus into a double-lobed "drop," to the point that nuclear fragments exceed the distances at which the nuclear force can hold two groups of charged nucleons together, and when this happens, the two fragments complete their separation and then are driven further apart by their mutually repulsive charges, in a process which becomes irreversible with greater and greater distance. A similar process occurs in [[fissionable]] isotopes (such as uranium-238), but in order to fission, these isotopes require additional energy provided by [[fast neutron]]s (such as those produced by [[nuclear fusion]] in [[thermonuclear weapons]]).
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=== Energetika ===
 
==== Ulaz ====
[[Image:Stdef2.png|150px|right|thumb|The stages of binary fission in a liquid drop model. Energy input deforms the nucleus into a fat "cigar" shape, then a "peanut" shape, followed by binary fission as the two lobes exceed the short-range [[nuclear force]] attraction distance, then are pushed apart and away by their electrical charge. In the liquid drop model, the two fission fragments are predicted to be the same size. The nuclear shell model allows for them to differ in size, as usually experimentally observed.]]
The fission of a heavy nucleus requires a total input energy of about 7 to 8 million [[electron volt]]s (MeV) to initially overcome the [[nuclear force]] which holds the nucleus into a spherical or nearly spherical shape, and from there, deform it into a two-lobed ("peanut") shape in which the lobes are able to continue to separate from each other, pushed by their mutual positive charge, in the most common process of binary fission (two positively charged fission products + neutrons). Once the nuclear lobes have been pushed to a critical distance, beyond which the short range [[strong force]] can no longer hold them together, the process of their separation proceeds from the energy of the (longer range) [[Electromagnetic force|electromagnetic]] repulsion between the fragments. The result is two fission fragments moving away from each other, at high energy.