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Isotopes Of Tungsten
Naturally occurring tungsten (74W) consists of five isotopes. Four are considered stable (182W, 183W, 184W, and 186W) and one is slightly radioactive, 180W, with an extremely long half-life of . On average, two alpha decays of 180W occur per gram of natural tungsten per year, so for most practical purposes, 180W can be considered stable. Theoretically, all five naturally occurring isotopes of tungsten can decay into isotopes of hafnium (element 72) by alpha emission, but only 180W has been observed to do so. The other naturally occurring isotopes have not been observed to decay (they are observationally stable), and lower bounds for their half-lives have been established: :182W, t1/2 > 7.7×1021 years :183W, t1/2 > 4.1×1021 years :184W, t1/2 > 8.9×1021 years :186W, t1/2 > 8.2×1021 years Thirty-four artificial radioisotopes of tungsten have been characterized with mass numbers ranging from 156 to 194, the most stable of which are 181W with a half-life of 121.2 da ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tungsten
Tungsten (also called wolfram) is a chemical element; it has symbol W and atomic number 74. It is a metal found naturally on Earth almost exclusively in compounds with other elements. It was identified as a distinct element in 1781 and first isolated as a metal in 1783. Its important ores include scheelite and wolframite, the latter lending the element its alternative name. The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all known elements, melting at . It also has the highest boiling point, at . Its density is 19.254 g/cm3, comparable with that of uranium and gold, and much higher (about 1.7 times) than that of lead. Polycrystalline tungsten is an intrinsically brittle and hard material (under standard conditions, when uncombined), making it difficult to work into metal. However, pure single-crystalline tungsten is more ductile and can be cut with a hard-steel hacksaw. Tungsten occurs in many alloys ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron Capture
Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. This process thereby changes a nuclear proton to a neutron and simultaneously causes the emission of an electron neutrino. : : or when written as a nuclear reaction equation, ^_e + ^_p -> ^_n + ^_ ν_e Since this single emitted neutrino carries the entire decay energy, it has this single characteristic energy. Similarly, the momentum of the neutrino emission causes the daughter atom to recoil with a single characteristic momentum. The resulting daughter nuclide, if it is in an excited state, then transitions to its ground state. Usually, a gamma ray is emitted during this transition, but nuclear de-excitation may also take place by internal conversion. Following capture of an inner electron from the atom, an outer elect ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotopes Of Tungsten
Naturally occurring tungsten (74W) consists of five isotopes. Four are considered stable (182W, 183W, 184W, and 186W) and one is slightly radioactive, 180W, with an extremely long half-life of . On average, two alpha decays of 180W occur per gram of natural tungsten per year, so for most practical purposes, 180W can be considered stable. Theoretically, all five naturally occurring isotopes of tungsten can decay into isotopes of hafnium (element 72) by alpha emission, but only 180W has been observed to do so. The other naturally occurring isotopes have not been observed to decay (they are observationally stable), and lower bounds for their half-lives have been established: :182W, t1/2 > 7.7×1021 years :183W, t1/2 > 4.1×1021 years :184W, t1/2 > 8.9×1021 years :186W, t1/2 > 8.2×1021 years Thirty-four artificial radioisotopes of tungsten have been characterized with mass numbers ranging from 156 to 194, the most stable of which are 181W with a half-life of 121.2 da ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotopes Of Hafnium
Natural hafnium (72Hf) consists of five observationally stable isotopes (176Hf, 177Hf, 178Hf, 179Hf, and 180Hf) and one very long-lived radioisotope, 174Hf, with a half-life of years. In addition, there are 34 known synthetic radioisotopes, the most stable of which is 182Hf with a half-life of years. This extinct radionuclide is used in hafnium–tungsten dating to study the chronology of planetary differentiation. No other radioisotope has a half-life over 1.87 years. Most isotopes have half-lives under 1 minute. There are also at least 27 nuclear isomers, the most stable of which is 178m2Hf with a half-life of 31 years. All isotopes of hafnium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed. List of isotopes , -id=Hafnium-153 , 153Hf , style="text-align:right" , 72 , style="text-align:right" , 81 , 152.97069(32)# , 400# ms 200 ns, , , 1/2+# , , , -id=Hafnium-1 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotopes Of Tantalum
Natural tantalum (73Ta) consists of two stable isotopes: 181Ta (99.988%) and 180mTa (0.012%). There are also 35 known artificial radioisotopes, the longest-lived of which are 179Ta with a half-life of 1.82 years, 182Ta with a half-life of 114.43 days, 183Ta with a half-life of 5.1 days, and 177Ta with a half-life of 56.56 hours. All other isotopes have half-lives under a day, most under an hour. There are also numerous isomers, the most stable of which (other than 180mTa) is 178m1Ta with a half-life of 2.36 hours. All isotopes and nuclear isomers of tantalum are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed. Tantalum has been proposed as a "Salted bomb, salting" material for nuclear weapons (cobalt is another, better-known salting material). A jacket of 181Ta, irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, would transmute into the radioactive isotope ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotopes Of Rhenium
Naturally occurring rhenium (75Re) is 37.4% 185Re, which is stable (although it is predicted to decay), and 62.6% 187Re, which is unstable but has a very long half-life (4.12×1010 years). Among elements with a known stable isotope, only indium and tellurium similarly occur with a stable isotope in lower abundance than the long-lived radioactive isotope. There are 36 other unstable isotopes recognized, the longest-lived of which are 183Re with a half-life of 70 days, 184Re with a half-life of 38 days, 186Re with a half-life of 3.7186 days, 182Re with a half-life of 64.0 hours, and 189Re with a half-life of 24.3 hours. There are also numerous isomers, the longest-lived of which are 186mRe with a half-life of 200,000 years and 184mRe with a half-life of 177.25 days. All others have half-lives less than a day. List of isotopes , -id=Rhenium-159 , 159Re , style="text-align:right" , 75 , style="text-align:right" , 84 , 158.98411(33)# , 40# μs , , , 1/2+# , , ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Observationally Stable
Stable nuclides are isotopes of a chemical element whose nucleons are in a configuration that does not permit them the surplus energy required to produce a radioactive emission. The nuclei of such isotopes are not radioactive and unlike radionuclides do not spontaneously undergo radioactive decay. When these nuclides are referred to in relation to specific elements they are usually called that element's stable isotopes. The 80 elements with one or more stable isotopes comprise a total of 251 nuclides that have not been shown to decay using current equipment. Of these 80 elements, 26 have only one stable isotope and are called monoisotopic. The other 56 have more than one stable isotope. Tin has ten stable isotopes, the largest number of any element. Definition of stability, and naturally occurring nuclides Most naturally occurring nuclides are stable (about 251; see list at the end of this article), and about 35 more (total of 286) are known to be radioactive with long enou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radionuclide
A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferred to one of its electrons to release it as a conversion electron; or used to create and emit a new particle (alpha particle or beta particle) from the nucleus. During those processes, the radionuclide is said to undergo radioactive decay. These emissions are considered ionizing radiation because they are energetic enough to liberate an electron from another atom. The radioactive decay can produce a stable nuclide or will sometimes produce a new unstable radionuclide which may undergo further decay. Radioactive decay is a random process at the level of single atoms: it is impossible to predict when one particular atom will decay. However, for a collection of atoms of a single nu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Primordial Nuclide
In geochemistry, geophysics and nuclear physics, primordial nuclides, also known as primordial isotopes, are nuclides found on Earth that have existed in their current form since before Earth was formed. Primordial nuclides were present in the interstellar medium from which the Solar System was formed, and were formed in, or after, the Big Bang, by nucleosynthesis in stars and supernovae followed by mass ejection, by cosmic ray spallation, and potentially from other processes. They are the stable nuclides plus the long-lived fraction of radionuclides surviving in the primordial solar nebula through planet accretion until the present; 286 such nuclides are known. Stability All of the known 251 stable nuclides, plus another 35 nuclides that have half-lives long enough to have survived from the formation of the Earth, occur as primordial nuclides. These 35 primordial radionuclides represent isotopes of 28 separate elements. Cadmium, tellurium, xenon, neodymium, samarium, osmi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isomeric Transition
A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy excited state levels (higher energy levels). "Metastable" describes nuclei whose excited states have half-lives of 10−9 seconds or longer, 100 to 1000 times longer than the half-lives of the excited nuclear states that decay with a "prompt" half life (ordinarily on the order of 10−12 seconds). Some references recommend seconds to distinguish the metastable half life from the normal "prompt" gamma-emission half-life. Occasionally the half-lives are far longer than this and can last minutes, hours, or years. For example, the nuclear isomer survives so long (at least years) that it has never been observed to decay spontaneously. The half-life of a nuclear isomer can even exceed that of the ground state of the same nuclide, as shown by as well as , , , , and multiple holmium isomers. Sometimes, the gamma decay from a metastable state is referred ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beta Decay
In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron transforms it into a proton by the emission of an electron accompanied by an antineutrino; or, conversely a proton is converted into a neutron by the emission of a positron with a neutrino in what is called ''positron emission''. Neither the beta particle nor its associated (anti-)neutrino exist within the nucleus prior to beta decay, but are created in the decay process. By this process, unstable atoms obtain a more stable ratio of protons to neutrons. The probability of a nuclide decaying due to beta and other forms of decay is determined by its nuclear binding energy. The binding energies of all existing nuclides form what is called the nuclear band or valley of stability. For either electron or positron emission to be energeticall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotope
Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemical element), but different nucleon numbers (mass numbers) due to different numbers of neutrons in their nuclei. While all isotopes of a given element have similar chemical properties, they have different atomic masses and physical properties. The term isotope is derived from the Greek roots isos (wikt:ἴσος, ἴσος "equal") and topos (wikt:τόπος, τόπος "place"), meaning "the same place"; thus, the meaning behind the name is that different isotopes of a single element occupy the same position on the periodic table. It was coined by Scottish doctor and writer Margaret Todd (doctor), Margaret Todd in a 1913 suggestion to the British chemist Frederick Soddy, who popularized the term. The number of protons within the atomic nuc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
