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Alpha Nuclide
An alpha nuclide is a nuclide that consists of an integer number of alpha particles. Alpha nuclides have equal, even numbers of protons and neutrons; they are important in stellar nucleosynthesis since the energetic environment within stars is amenable to fusion of alpha particles into heavier nuclei. Stable alpha nuclides, and stable decay products of radioactive alpha nuclides, are some of the most common metals in the universe. Alpha nuclide is also short for '' alpha-emitting nuclide'', referring to those radioactive isotopes that undergo alpha decay Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus). The parent nucleus transforms or "decays" into a daughter product, with a mass number that is reduced by four and an a ... and thereby emit alpha particles. List of alpha nuclides The entries for 36Ar and 40Ca are theoretical: they would release energy on decay, but the process has never been observed, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclide
Nuclides (or nucleides, from nucleus, also known as nuclear species) are a class of atoms characterized by their number of protons, ''Z'', their number of neutrons, ''N'', and their nuclear energy state. The word ''nuclide'' was coined by the American nuclear physicist Truman P. Kohman in 1947. Kohman defined ''nuclide'' as a "species of atom characterized by the constitution of its nucleus" containing a certain number of neutrons and protons. The term thus originally focused on the nucleus. Nuclide vs. isotope A nuclide is an atom with a specific number of protons and neutrons in its nucleus, for example carbon-13 with 6 protons and 7 neutrons. The term was coined deliberately is distinction from isotope in order to consider the nuclear properties independently of the chemical properties, though ''isotope' is still used for that purpose especially where ''nuclide'' might be unfamiliar as in nuclear technology and nuclear medicine. For nuclear propeties, the number of neutrons ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alpha Particle
Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay but may also be produced in different ways. Alpha particles are named after the first letter in the Greek alphabet, α. The symbol for the alpha particle is α or α2+. Because they are identical to helium nuclei, they are also sometimes written as He2+ or 2+ indicating a helium ion with a +2 charge (missing its two electrons). Once the ion gains electrons from its environment, the alpha particle becomes a normal (electrically neutral) helium atom . Alpha particles have a net spin of zero. When produced in standard alpha radioactive decay, alpha particles generally have a kinetic energy of about 5 MeV and a velocity in the vicinity of 4% of the speed of light. They are a highly ionizing form of particle radiation, with low penetration depth (stopped b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proton
A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an electron (the proton-to-electron mass ratio). Protons and neutrons, each with a mass of approximately one Dalton (unit), dalton, are jointly referred to as ''nucleons'' (particles present in atomic nuclei). One or more protons are present in the Atomic nucleus, nucleus of every atom. They provide the attractive electrostatic central force which binds the atomic electrons. The number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number (represented by the symbol ''Z''). Since each chemical element, element is identified by the number of protons in its nucleus, each element has its own atomic number, which determines the number of atomic electrons and consequently the chemical characteristi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neutron
The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nuclear fission in 1938, the first self-sustaining nuclear reactor (Chicago Pile-1, 1942) and the first nuclear weapon (Trinity (nuclear test), Trinity, 1945). Neutrons are found, together with a similar number of protons in the atomic nucleus, nuclei of atoms. Atoms of a chemical element that differ only in neutron number are called isotopes. Free neutrons are produced copiously in nuclear fission and nuclear fusion, fusion. They are a primary contributor to the nucleosynthesis of chemical elements within stars through fission, fusion, and neutron capture processes. Neutron stars, formed from massive collapsing stars, consist of neutrons at the density of atomic nuclei but a total mass more than the Sun. Neutron properties and interactions ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stellar Nucleosynthesis
In astrophysics, stellar nucleosynthesis is the creation of chemical elements by nuclear fusion reactions within stars. Stellar nucleosynthesis has occurred since the original creation of hydrogen, helium and lithium during the Big Bang. As a predictive theory, it yields accurate estimates of the observed abundances of the elements. It explains why the observed abundances of elements change over time and why some elements and their isotopes are much more abundant than others. The theory was initially proposed by Fred Hoyle in 1946, who later refined it in 1954. Further advances were made, especially to nucleosynthesis by neutron capture of the elements heavier than iron, by Margaret and Geoffrey Burbidge, William Alfred Fowler and Fred Hoyle in their famous 1957 B2FH paper, which became one of the most heavily cited papers in astrophysics history. Stars evolve because of changes in their composition (the abundance of their constituent elements) over their lifespans, f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metal (astronomy)
In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-dark) matter in the universe is either hydrogen or helium, and astronomers use the word ''metals'' as convenient shorthand for ''all elements except hydrogen and helium''. This word-use is distinct from the conventional chemical or physical definition of a metal as an electrically conducting element. Stars and nebulae with relatively high abundances of heavier elements are called ''metal-rich'' when discussing metallicity, even though many of those elements are called ''nonmetals'' in chemistry. Metals in early spectroscopy In 1802, William Hyde WollastonMelvyn C. UsselmanWilliam Hyde WollastonEncyclopædia Britannica, retrieved 31 March 2013 noted the appearance of a number of dark features in the solar spectrum. In 1814, Joseph von Fraunhofer independently rediscovered the lines and began to systematically st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Alpha-emitting Nuclides
The following are among the principal radionuclides known to undergo alpha decay, emitting alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay but may also be produce ...s. * , , , * , , , , , , * , , * , , , , * * , , * , * , , , , * * , , , , * * , , , * * , , * , {{SimpleNuclide, californium, 252, link=yes See also * Common beta emitters * Commonly used gamma-emitting isotopes Alpha emitting Alpha emitting ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alpha Decay
Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus). The parent nucleus transforms or "decays" into a daughter product, with a mass number that is reduced by four and an atomic number that is reduced by two. An alpha particle is identical to the nucleus of a helium-4 atom, which consists of two protons and two neutrons. It has a charge of and a mass of , and is represented as ^_\alpha. For example, uranium-238 undergoes alpha decay to form thorium-234. While alpha particles have a charge , this is not usually shown because a nuclear equation describes a nuclear reaction without considering the electrons – a convention that does not imply that the nuclei necessarily occur in neutral atoms. Alpha decay typically occurs in the heaviest nuclides. Theoretically, it can occur only in nuclei somewhat heavier than nickel (element 28), where the overall binding energy per nucleon is no longer a maximum a ... [...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] |
Double Electron Capture
Double electron capture is a decay mode of an atomic nucleus. For a nuclide (''A'', ''Z'') with a number of nucleons ''A'' and atomic number ''Z'', double electron capture is only possible if the mass of the nuclide (''A'', ''Z''−2) is lower. In this mode of decay, two of the orbital electrons are captured via the weak interaction by two protons in the nucleus, forming two neutrons (Two neutrinos are emitted in the process). Since the protons are changed to neutrons, the number of neutrons increases by two, while the number of protons ''Z'' decreases by two, and the atomic mass number ''A'' remains unchanged. As a result, by reducing the atomic number by two, double electron capture transforms the nuclide into a different element. Example: : Rarity In most cases this decay mode is masked by other, more probable modes involving fewer particles, such as single electron capture. When all other modes are “forbidden” (strongly suppressed) double electron capture becomes the m ... [...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] |
