Uranium 238 Atomic Number

Uranium—(Planet Uranus), U; atomic weight 238.029; atomic number 92; melting point 1132.3 ± 0.8°C; boiling point 3818°C; specific gravity ~ 18.95; valence 2, 3, 4, 5, or 6. Yellow-colored glass, containing more than 1 % uranium oxide and dating back to 79 A.D., has been found near Naples, Italy. Klaproth recognized an unknown element in pitchblende and attempted to isolate the metal in 1789. The metal apparently was first isolated in 1841 by Peligot, who reduced the anhydrous chloride with potassium. Uranium is not as rare as it was once thought. It is now considered to be more plentiful than mercury, antimony, silver, or cadmium, and is about as abundant as molybdenum or arsenic. It occurs in numerous minerals such as pitchblende, uraninite, carnotite, autunite, uranophane, davidite, and tobernite. It is also found in phosphate rock, lignite, monazite sands, and can be recovered commercially from these sources. The A.E.C. purchases uranium in the form of acceptable U₃O₈ concentrates. This incentive program has greatly increased the known uranium reserves. Uranium can be prepared by reducing uranium halides with alkali or alkaline earth metals or by reducing uranium oxides by calcium, aluminum, or carbon at high temperatures. What is cinema 4d for mac.

Nuclear fuels are used to generate electrical power, to make isotopes, and to make weapons. Much of the internal heat of the earth is thought to be due to the presence of uranium and thorium. Uranium-238, with a half-life of 4.51 x 10 9 years, is used to estimate the age of igneous rocks. Uranium may be used to harden and strengthen steel.

The metal can also be produced by electrolysis of KUF₅ or UF₄, dissolved in a molten mixture of CaCl₂ NaCl. High-purity uranium can be prepared by the thermal decomposition of uranium halides on a hot filament.

Name: Uranium: Symbol: U: Atomic Number: 92: Atomic Mass: 238.029 atomic mass units: Number of Protons: 92: Number of Neutrons: 146: Number of Electrons: 92: Melting. Plutonium was first synthetically produced and isolated in late 1940 and early 1941, by a deuteron bombardment of uranium-238 in the 1.5-metre cyclotron at the University of California, Berkeley. First, neptunium-238 was synthesized, which subsequently beta-decayed to form the new element with atomic number 94 and atomic weight 238. Since uranium had been named after the planet Uranus. Uranium is a radioactive element with atomic symbol U, atomic number 92, and atomic weight 238. NCI Thesaurus (NCIt) Uranium, radium, and radon are naturally occurring radionuclides found in.

Uranium exhibits three crystallographic modifications as follows:

Uranium is a heavy, silvery-white metal which is pyrophoric when finely divided. It is a little softer than steel, and is attacked by cold water in a finely divided state. It is malleable, ductile, and slightly paramagnetic. In air, the metal becomes coated with a layer of oxide. Acids dissolve the metal, but it is unaffected by alkalis. Uranium has fourteen isotopes, all of which are radioactive. Naturally occurring uranium nominally contains 99.2830% by weight U²³⁸, 0.7110% U²³⁵, and 0.0054% U²³⁴. Studies show that the percentage weight of U²³⁵ in natural uranium varies by as much as 0.1%, depending on the source. The A.E.C. has adopted the value of 0.711 as being their 'official' percentage of U²³⁵ in natural uranium. Natural uranium is sufficiently radioactive to expose a photographic plate in an hour or so.

Much of the internal heat of the earth is thought to be attributable to the presence of uranium and thorium. U²³⁸ with a half-life of 4.51 × 10⁹ years, has been used to estimate the age of igneous rocks. The origin of uranium, the highest member of the naturally occurring elements—except perhaps for traces of neptunium or plutonium—is not clearly understood, although it may be presumed that uranium is a decay product of elements of higher atomic weight, which may have once been present on earth or elsewhere in the universe. These original elements may have been created as a result of a primordial 'creation,' known as 'the big bang,' in a supernovae, or in some other stellar processes.

Uranium is of great importance as a nuclear fuel. U²³⁸ can be converted into fissionable plutonium by the following reactions:

Uranium 238 Decay Process

This nuclear conversion can be brought about in 'breeder' reactors where it is possible to produce more new fissionable material than the fissionable material used in maintaining the chain reaction. U²³⁵ is of even greater importance, for it is the key to the utilization of uranium. U²³⁵, while occurring in natural uranium to the extent of only 0.71%, is so fissionable with slow neutrons that a self-sustaining fission chain reaction can be made to occur in a reactor constructed from natural uranium and a suitable moderator, such as heavy water or graphite, alone. U²³⁵ can be concentrated by gaseous diffusion and other physical processes, if desired, and used directly as a nuclear fuel, instead of natural uranium, or used as an explosive. Natural uranium, slightly enriched with U²³⁵ by a small percentage, is used to fuel nuclear power reactors for the generation of electricity. Natural thorium can be irradiated with neutrons as follows to produce the important isotope U²³³

While thorium itself is not fissionable, U²³³ is, and in this way may be used as a nuclear fuel. One pound of completely fissioned uranium has the fuel value of over 1500 tons of coal. The uses of nuclear fuels to generate electrical power, to make isotopes for peaceful purposes, and to make explosives are well known. Uranium in the U.S.A. is controlled by the Atomic Energy Commission. New uses are being found for 'depleted uranium, i.e., uranium with the percentage of U²³⁵ lowered to about 0.2%. It has found use in inertial guidance devices, gyro compasses, counterweights for aircraft control surfaces, as ballast for missile reentry vehicles, and as a shielding material. Uranium metal is used for X-ray targets for production of high-energy X-rays; the nitrate has been used as photographic toner, and the acetate is used in analytical chemistry. Crystals of uranium nitrate are triboluminescent. Uranium salts have also been used for producing yellow 'vaseline' glass and glazes. Uranium and its compounds are highly toxic, both from a chemical and radiological standpoint. Finely divided uranium metal, being pyrophoric, presents a fire hazard. The maximum recommended allowable concentration of soluble uranium compound in air (based on chemical toxicity) is 0.05 mg/M³ (8-hr time-weighted average—40-hr week); for insoluble compounds the concentration is set at 0.25 mg/M³ Cs for mac steam. of air. The maximum permissible total body burden of natural uranium (based on radiotoxicity) is 0.2μCi for soluble compounds.

Charts for mac os x. Nuclear fission is one type of nuclear transmutation where a heavier nucleus, when bombarded with the neutron, splits into two or more lighter neutrons. It is also accompanied by the release of one or more neutrons and thermal energy owing to mass defect. Human has already mastered the nuclear fission reaction, and now-a-days it is extensively used in nuclear reactors for electricity or power generation and also in nuclear weapons. In nuclear reactors, fission is initiated by either thermal neutrons (0.025eV energy corresponding to the velocity of 2.2 km/s) or fast neutrons (1 – 10MeV energy corresponding to the velocity of about 5×10⁴ km/s). Prompt neutrons that are released as fission products can also initiate fission of other intact isotopes available within the fuel, which ultimately leads to the formation of much desirable self-sustained chain reaction. However, every radioactive isotope cannot sustain chain reaction. Thus any radioactive isotope cannot be used as nuclear fuel. Only three isotopes are considered chemically and economically suitable for this purpose, namely Uranium-233, Uranium-235 and Plutonium-239. These three are thus termed as fissile isotopes. Among these three, U-235 is the only naturally available one. However, its availability is very low (only about 0.7%) as natural uranium mostly contains Uranium-238 (about 99.3%).

Even though U-238 is abundantly available on Earth, it is not one fissile isotope as it fails to sustain the much desired chain reaction, and thus it cannot be used as nuclear fuel. Hence the proportion of U-235 within the natural uranium is required to increase artificially for the use as fuel in nuclear reactors. Such a process of increasing percentage of U-235 is called uranium enrichment. Typically, thermal reactors require 3 – 5% enriched fuel (except PHWR where no enrichment is usually required as it uses heavy water as coolant-cum-moderator), while fast breeder reactors require 15 – 20% enriched fuel. Above 90% enrichment is necessary for weapon grade uranium fuel. Whatever be the enrichment, only U-235 isotopes participate in fission reaction. Accordingly, only a tiny portion of the uranium fuel is utilized for heat generation in the nuclear reactors, while majority of the fuel remains unutilized. Thus the uranium fuel for reactors in the nuclear power plant contains both U-238 and U-235 isotopes in different proportions based on the enrichment, but only U-235 undergoes nuclear fission to generate necessary thermal energy. Various similarities and differences between Uranium-235 and Uranium-238 isotopes are given below in table format.

U-235 and U-238 are two isotopes of uranium. Both contain same number of electrons and protons (92 each).
Both the isotopes are naturally available; however, their abundancy has wide gap. While about 99.28% of the entire Earth’s uranium is basically U-238, only a meagre 0.72% is U-235.
Both the isotopes are radioactive, although they have different half-lives.
Nuclear fuel that is used in reactors of the nuclear power plant contains both the isotopes in varying proportions. However, only U-235 participated in fission, while the other one remains intact.

Uranium-235	Uranium-238
An electrically neutral uranium-235 isotope contains 92 electrons, 92 protons and 143 neutrons (i.e. e = 92, p = 92, n = 143). So its atomic number is 92 and mass number is 235.	An electrically neutral uranium-238 isotope contains 92 electrons, 92 protons and 146 neutrons (i.e. e = 92, p = 92, n = 146). So its atomic number is 92 and mass number is 238.
Even though uranium is abundantly available on Earth, the uranium-235 isotope has low abundancy (only about 0.72% of the entire Earth’s uranium is U-235).	Uranium-238 isotope is most common isotope of uranium found on Earth (about 99.28% of the entire Earth’s uranium is basically U-238).
Its half-life (t_1/2) is approximately 0.7038 ´ 10⁹ years.	Its half-life (t_1/2) is approximately 4.468 ´ 10⁹ years.
Its atomic mass is about 235.043u. It is slightly lighter than U-238. This mass difference is used for enriching purposes (gaseous diffusion and gas centrifuge).	It is slightly heavier than U-235. Its atomic mass is about 238.05u.
It has higher probability of alpha-decay and thus it is less stable.	Chance of alpha-decay is less for U-238 and thus it is more stable.
Owing to spontaneous disintegration (natural radioactivity), U-235 undergoes alpha-decay to produce thorium-231 isotope (₉₀Th²³¹).	U-238 also undergoes alpha-decay spontaneously but produces thorium-234 isotope (₉₀Th²³⁴).
Uranium-235 is one fissile isotope, thus it can sustain nuclear fission chain reaction with thermal neutron.	Uranium-238 is not a fissile isotope and thus cannot sustain chain reaction with any neutron. However, U-238 is one fertile material and thus it can produce Pu-239 (one fissile isotope) by nuclear breeding in fast breeder reactor.
Its fission cross-section with thermal neutron is around 583 barns, and that with fast neutron is about 1 barn.	Its fission cross-section with thermal neutron is as low as 0.00002 barn, and that with fast neutron is about 0.3 barn.
It is the active constituent of nuclear fuel. Thus natural uranium is enriched with U-235 (3 – 5% enrichment is required for light water thermal reactors, 15 – 20% enrichment is required for fast reactors, while about 90% enrichment is required for nuclear weapon). Only U-235 isotopes in the entire fuel undergo nuclear fission to liberate heat energy.	Even though a significant part of the nuclear fuel is made up of U-238, mostly it does not participate in nuclear fission reaction and thus it is not the active part of nuclear fuel. In thermal reactors, entire U-238 remains intact after complete fuel burn-up. However, a small portion of U-238 can breed into Pu-239 in fast breeder reactors, and this Pu-239 can participate in nuclear fission to generate heat.
In nuclear fission, when an atom of uranium-235 splits into krypton and barium, it liberates 202.5MeV energy (arises from mass defect in reaction).	It usually does not undergo nuclear fission reaction to liberate energy because of its very low fission cross-section.

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