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Encyclopedia > Oklo

Oklo is a place in the West African state of Gabon. West Africa is the region of western Africa that, most strictly speaking, includes the countries of Benin, Burkina Faso, Côte dIvoire, The Gambia, Ghana, Guinea, Guinea-Bissau, Liberia, Mali, Niger, Nigeria, Senegal, Sierra Leone and Togo. ...


It is famous as the locale of a number of sites (so far 16 zones discovered) at which self-sustaining nuclear fission reactions took place approximately 2 billion years ago. This fact was discovered in 1972, by French physicist Francis Perrin. Measurements of the relative abundances of the two most significant isotopes of the uranium mined there showed an anomalous result compared to those obtained for uranium from other mines. The levels were not merely detectable by statistical analysis: in some samples they were reduced to half what would have been expected. At first nuclear skullduggery was feared. Sketch of induced nuclear fission, a neutron (n) strikes a uranium nucleus which splits into similar products (F. P.), and releases more neutrons to continue the process, and energy in the form of gamma and other radiation. ... A nuclear reactor is a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate (as opposed to a nuclear explosion, where the chain reaction occurs in a split second). ... 1972 was a leap year that started on a Saturday. ... Francis Perrin (Paris, 1901 - id. ... Isotopes are forms of an element whose nuclei have the same atomic number–-the number of protons in the nucleus--but different atomic masses because they contain different numbers of neutrons. ... General Name, Symbol, Number uranium, U, 92 Chemical series actinides Group, Period, Block ?, 7, f Appearance silvery gray metallic Atomic mass 238. ...


The natural nuclear reactor formed when a uranium-rich mineral deposit became inundated with groundwater that acted as a neutron moderator, and a strong chain reaction took place. The water moderator would boil away as the reaction increased, slowing it back down again and preventing a meltdown. The fission reaction was sustained for hundreds of thousands of years. Groundwater is water flowing within aquifers below the water table. ... In nuclear engineering, a neutron moderator is a medium which reduces the velocity of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction. ...


A key to the creation was that at the time, the abundance of fissionable U-235 was about 3%, which is comparable to the amount used in today's reactors. Due to U-235's shorter half life than U-238, the current abundance of U-235 in natural uranium is about 0.7%. Therefore a natural nuclear reactor is no longer possible on Earth. Uranium-235 is an isotope of uranium that differs from the elements other common isotope, uranium-238, by its ability to cause a rapidly expanding fission chain reaction. ... Half-Life is a science fiction first-person shooter computer game developed by Valve Software and published by Sierra Entertainment in 1998, based on a heavily-modified Quake game engine. ... There are two objects with this name: Unterseeboot 238 Uranium-238, the most common isotope of uranium This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...


The natural reactor of Oklo can also be used to check if the fine-structure constant α might have changed over time, since there is no physical reason why it should be exactly constant. Alex Shlyakhter proposed in 1976 to measure the abundance of Sm-149 to estimate the cross section for neutron capture of this isotope at that time and check it against the present value. The fine-structure constant or Sommerfeld fine-structure constant, usually denoted , is the fundamental physical constant characterizing the strength of the electromagnetic interaction. ... Cross section may refer to the following In geometry, Cross section is the intersection of a 3-dimensional body with a plane. ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ... Isotopes are forms of an element whose nuclei have the same atomic number–-the number of protons in the nucleus--but different atomic masses because they contain different numbers of neutrons. ...


Relation To Yucca Mountain

The US government assessment of the security of Yucca mountain for spent nuclear fuel storage, drew comparisons with Oklo. Yucca Mountain Yucca Mountain is a ridge-line in Nye County, Nevada; composed of volcanic material (mostly tuff) ejected from a now-extinct caldera-forming supervolcano. ...

"And when these deep underground natural nuclear chain reactions were over, nature showed that it could effectively contain the radioactive wastes created by the reactions. No nuclear chain reactions will ever happen in a repository for high-level nuclear wastes. But if a repository were to be built at Yucca Mountain, scientists would count on the geology of the area to contain radionuclides generated by these wastes with similar effectiveness."

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  Results from FactBites:
 
Oklo - Wikipedia, the free encyclopedia (425 words)
Oklo is a place in the West African state of Gabon.
The natural reactor of Oklo can also be used to check if the fine-structure constant α might have changed over time, since there is no physical reason why it should be exactly constant.
Alex Shlyakhter proposed in 1976 to measure the abundance of Sm-149 to estimate the cross section for neutron capture of this isotope at that time and check it against the present value.
astronomy news (1994 words)
The Oklo reactor started up nearly two billion years ago when groundwater filtered through crevices in the rocks and mixed with uranium ore to trigger a fission reaction that was sustained for hundreds of thousands of years.
Several studies that have analysed the relative concentrations of radioactive isotopes left behind at Oklo have concluded that nuclear reactions then were much the same as they are today, which implies alpha was the same too.
It seems that the Oklo reactors didn't plunge straight into a runaway chain reaction, or meltdown of the veins because of the presence of water in the rocks.
  More results at FactBites »

 
 

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