"between atoms. By this mechanism, atoms are able to bond into molecules and other types of chemical compounds like ionic and covalent network crystals. By definition, any two atoms with an identical number of ""protons"" in their nuclei belong to the same chemical element. Atoms with equal numbers of protons but a different number of ""neutrons"" are different isotopes of the same element. For example, all hydrogen atoms admit exactly one proton, but isotopes exist with no neutrons (hydrogen-1, by far the most common form, also called protium), one neutron (deuterium), two neutrons (tritium) and more than two neutrons. The"
"electrons as protons. Thus different isotopes of a given element all have the same number of electrons and share a similar electronic structure. Because the chemical behavior of an atom is largely determined by its electronic structure, different isotopes exhibit nearly identical chemical behavior. The main exception to this is the kinetic isotope effect: due to their larger masses, heavier isotopes tend to react somewhat more slowly than lighter isotopes of the same element. This is most pronounced by far for protium (), deuterium (), and tritium (), because deuterium has twice the mass of protium and tritium has three"
"Promethium Promethium is a chemical element with symbol Pm and atomic number 61. All of its isotopes are radioactive; it is extremely rare, with only about 500-600 grams naturally occurring in Earth's crust at any given time, and one of only two such elements that are followed in the periodic table by elements with stable forms, a distinction shared with technetium. Chemically, promethium is a lanthanide. Promethium shows only one stable oxidation state of +3. In 1902 Bohuslav Brauner suggested that there was a then-unknown element with properties intermediate between those of the known elements neodymium (60) and samarium (62);"
"u) is known as ""tritium"" and contains one proton and two neutrons in its nucleus. It is radioactive, decaying into helium-3 through β− decay with a half-life of 12.32 years. Trace amounts of tritium occur naturally because of the interaction of cosmic rays with atmospheric gases. Tritium has also been released during nuclear weapons tests. It is used in thermonuclear fusion weapons, as a tracer in isotope geochemistry, and specialized in self-powered lighting devices. The most common method of producing tritium is by bombarding a natural isotope of lithium, lithium-6, with neutrons in a nuclear reactor. Tritium was once used"
"than with more protons than neutrons. (There are many such unstable isotopes, the lightest being and .) There is only a trace amount (0.000137%) of on Earth, primarily present since the formation of the Earth, although some falls to Earth trapped in cosmic dust. Trace amounts are also produced by the beta decay of tritium. In stars, however, is more abundant, a product of nuclear fusion. Extraplanetary material, such as lunar and asteroid regolith, has trace amounts of from solar wind bombardment. For helium-3 to form a superfluid, it must be cooled to a temperature of 0.0025 K, or almost"
"The symbols D and T (instead of and ) are sometimes used for deuterium and tritium, but the corresponding symbol for protium, P, is already in use for phosphorus and thus is not available for protium. In its nomenclatural guidelines, the International Union of Pure and Applied Chemistry (IUPAC) allows any of D, T, , and to be used, although and are preferred. The exotic atom muonium (symbol Mu), composed of an antimuon and an electron, is also sometimes considered as a light radioisotope of hydrogen, due to the mass difference between the antimuon and the electron. Muonium was discovered"
"as a relatively weak beta reaction, so the radioactivity cannot permeate skin. Tritium is thus only hazardous if directly ingested or inhaled. Protium is a spin 1/2 subatomic particle and is therefore a fermion. Other fermions include neutrons, electrons, and the radioactive isotope tritium. Fermions are governed by Pauli's exclusion principle, where no two particles can have the same quantum number. However, bosons like deuterium and photons, are not bound by exclusion and multiple particles can occupy the same energy state. This fundamental difference in H and H manifests in many physical properties. Integer spin particles like deuterium follow Bose-Einstein"
"proton emission to helium-3. Lithium-4 can be formed as an intermediate in some nuclear fusion reactions. Lithium-6 is valuable as the source material for the production of tritium (hydrogen-3) and as an absorber of neutrons in nuclear fusion reactions. Natural lithium contains about 7.5 percent lithium-6, with the rest being lithium-7. Large amounts of lithium-6 have been separated out for placing into hydrogen bombs. The separation of lithium-6 has by now ceased in the large thermonuclear powers, but stockpiles of it remain in these countries. Lithium-6 is one of only three stable isotopes with a spin of 1, the others"
"of the theory up to that time, due to its contrasting more clearly with its neighboring elements than the two previously confirmed predictions of Mendeleev do with theirs. The existence of an element between thorium and uranium was predicted by Mendeleev in 1871. In 1900 William Crookes isolated protactinium as a radioactive material from uranium, which he could not identify. Different isotopes of protactinium were identified in Germany in 1913 and in 1918, but the name ""protactinium"" was not given until 1948. Since the 1950s thorium, uranium and protactinium have been classified as actinides; hence protactinium does not occupy the"
"of Great Britain, independently discovered another isotope of protactinium, Pa having a much longer half-life of about 32,000 years. Thus the name ""brevium"" was changed to ""protoactinium"" as the new element was part of the decay chain of uranium-235 as the parent of actinium (from = ""protos"" meaning ""first"", ""before""). For ease of pronunciation, the name was shortened to ""protactinium"" by the IUPAC in 1949. The discovery of protactinium completed one of the last gaps in the early versions of the periodic table, proposed by Mendeleev in 1869, and it brought to fame the involved scientists. Aristid von Grosse produced"
"today's deuterium originated from this proton-proton fusion after sufficient cooling. Tritium, or hydrogen-3, with one proton and two neutrons, was produced by proton and neutron collisions in the early universe as well, but it has since radioactively decayed to helium-3. Modern tritium cannot be explained by big bang nucleosynthesis because of tritium's short half-life of 12.3 years. Today's tritium concentration is instead governed by nuclear reactions and cosmic rays. The radioactive beta decay of tritium to helium releases an electron and an antineutrino, with an average energy release of 18.6 MeV. It is important to note that this is classified"
"and from natural gas wells. Other than protium (ordinary hydrogen), helium-3 is the only stable isotope of any element with more protons than neutrons. Helium-3 occurs as a primordial nuclide, escaping from the Earth's crust into the atmosphere and into outer space over millions of years. Helium-3 is also thought to be a natural nucleogenic and cosmogenic nuclide, one produced when lithium is bombarded by natural neutrons, which can be released by spontaneous fission and by nuclear reactions with cosmic rays. Some of the helium-3 found in the terrestrial atmosphere is also a relic of atmospheric and underwater nuclear weapons"
"Tritium's specific activity is . Tritium figures prominently in studies of nuclear fusion because of its favorable reaction cross section and the large amount of energy (17.6 MeV) produced through its reaction with deuterium: All atomic nuclei, being composed of protons and neutrons, repel one another because of their positive charge. However, if the atoms have a high enough temperature and pressure (for example, in the core of the Sun), then their random motions can overcome such electrical repulsion (called the Coulomb force), and they can come close enough for the strong nuclear force to take effect, fusing them into"
"of protactinium (with Otto Hahn), and one of the discoverers of nuclear fission. In 1994 the name was recommended by IUPAC, and was officially adopted in 1997. It is thus the only element named specifically after a non-mythological woman (curium being named for both Pierre and Marie Curie). Meitnerium has no stable or naturally occurring isotopes. Several radioactive isotopes have been synthesized in the laboratory, either by fusing two atoms or by observing the decay of heavier elements. Eight different isotopes of meitnerium have been reported with atomic masses 266, 268, 270, and 274–278, two of which, meitnerium-268 and meitnerium-270,"
"Protactinium Protactinium (formerly protoactinium) is a chemical element with symbol Pa and atomic number 91. It is a dense, silvery-gray actinide metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds in which protactinium is usually present in the oxidation state +5, but it can also assume +4 and even +3 or +2 states. Concentrations of protactinium in the Earth's crust are typically a few parts per trillion, but may reach up to a few parts per million in some uraninite ore deposits. Because of its scarcity, high radioactivity and high toxicity, there are"
"The combination of δC and Pa/Th can therefore provide a more complete insight into past circulation changes. Tritium was released to the atmosphere during atmospheric testing of nuclear bombs. Radioactive decay of tritium produces the noble gas helium-3. Comparing the ratio of tritium to helium-3 (H/He) allows estimation of the age of recent ground waters. Isotope geochemistry Isotope geochemistry is an aspect of geology based upon the study of natural variations in the relative abundances of isotopes of various elements. Variations in isotopic abundance are measured by isotope ratio mass spectrometry, and can reveal information about the ages and origins"
"Praseodymium Praseodymium is a chemical element with symbol Pr and atomic number 59. It is the third member of the lanthanide series and is traditionally considered to be one of the rare-earth metals. Praseodymium is a soft, silvery, malleable and ductile metal, valued for its magnetic, electrical, chemical, and optical properties. It is too reactive to be found in native form, and pure praseodymium metal slowly develops a green oxide coating when exposed to air. Praseodymium always occurs naturally together with the other rare-earth metals. It is the fourth most common rare-earth element, making up 9.1 parts per million of"
"persisted down to the present because their rate of decay is so slow (e.g. uranium-238 and potassium-40). Post-primordial isotopes were created by cosmic ray bombardment as cosmogenic nuclides (e.g., tritium, carbon-14), or by the decay of a radioactive primordial isotope to a radioactive radiogenic nuclide daughter (e.g. uranium to radium). A few isotopes are naturally synthesized as nucleogenic nuclides, by some other natural nuclear reaction, such as when neutrons from natural nuclear fission are absorbed by another atom. As discussed above, only 80 elements have any stable isotopes, and 26 of these have only one stable isotope. Thus, about two-thirds"
"Deuterium Deuterium (or hydrogen-2, symbol ' or ', also known as heavy hydrogen) is one of two stable isotopes of hydrogen (the other being protium, or hydrogen-1). The nucleus of deuterium, called a deuteron, contains one proton and one neutron, whereas the far more common protium has no neutron in the nucleus. Deuterium has a natural abundance in Earth's oceans of about one atom in of hydrogen. Thus deuterium accounts for approximately 0.0156% (or, on a mass basis, 0.0312%) of all the naturally occurring hydrogen in the oceans, while protium accounts for more than 99.98%. The abundance of deuterium changes"
"Deuterium Deuterium (or hydrogen-2, symbol ' or ', also known as heavy hydrogen) is one of two stable isotopes of hydrogen (the other being protium, or hydrogen-1). The nucleus of deuterium, called a deuteron, contains one proton and one neutron, whereas the far more common protium has no neutron in the nucleus. Deuterium has a natural abundance in Earth's oceans of about one atom in of hydrogen. Thus deuterium accounts for approximately 0.0156% (or, on a mass basis, 0.0312%) of all the naturally occurring hydrogen in the oceans, while protium accounts for more than 99.98%. The abundance of deuterium changes"
"in 1988. When deuterium and tritium fuse, two nuclei come together to form a helium nucleus (an alpha particle), and a high-energy neutron. While nearly all stable isotopes lighter on the periodic table than iron-56 and nickel-62, which have the highest binding energy per nucleon, will fuse with some other isotope and release energy, deuterium and tritium are by far the most attractive for energy generation as they require the lowest activation energy (thus lowest temperature) to do so, while producing among the most energy per unit weight. All proto- and mid-life stars radiate enormous amounts of energy generated by"
"element with the symbol Po and atomic number 84, discovered in 1898 by Marie Skłodowska-Curie and Pierre Curie. A rare and highly radioactive element, polonium is chemically similar to bismuth and tellurium, and it occurs in uraniumores. Polonium has been studied for possible use in heating spacecraft. As it is unstable, all isotopes of polonium are radioactive. There is disagreement as to whether polonium is a post-transition metal or metalloid. Astatine is a radioactive chemical element with the symbol At and atomic number 85. It occurs on the Earth only as the result of decay of heavier elements, and decays"
"Polonium Polonium is a chemical element with symbol Po and atomic number 84. A rare and highly radioactive metal with no stable isotopes, polonium is chemically similar to selenium and tellurium, though its metallic character resembles that of its horizontal neighbors in the periodic table: thallium, lead, and bismuth. Due to the short half-life of all its isotopes, its natural occurrence is limited to tiny traces of the fleeting polonium-210 (with a half-life of 138 days) in uranium ores, as it is the penultimate daughter of natural uranium-238. Though slightly longer-lived isotopes exist, they are much more difficult to produce."
"expected. For example, the nuclides tin-100 and tin-132 are examples of doubly magic isotopes of tin that are unstable, and represent endpoints beyond which stability drops off rapidly. Nickel-48, discovered in 1999, is the most proton-rich isotope known beyond helium-3. At the other extreme, nickel-78 is also doubly magical, with 28 protons and 50 neutrons, a ratio observed only in much heavier elements apart from tritium with one proton and two neutrons (Ni-78: 28/50 = 0.56; U-238: 92/146 = 0.63). In December 2006, hassium-270, with 108 protons and 162 neutrons, was discovered by an international team of scientists led by"
"comprise the others. There are 41 odd-numbered elements with ""Z"" = 1 through 81, of which 30 (including hydrogen, since zero is an even number) have one stable odd-even isotope, the elements technetium () and promethium () have no stable isotopes, and nine elements: chlorine (), potassium (), copper (), gallium (), bromine (), silver (), antimony (), iridium (), and thallium (), have two odd–even stable isotopes each. This makes a total of 30×1 + 9×2 = 48 stable odd–even isotopes. There are also five primordial long-lived radioactive odd–even isotopes, , , , , and . The last two"
"to store thorium in proposed future thorium nuclear reactors. Thorium forms eutectic mixtures with chromium and uranium, and it is completely miscible in both solid and liquid states with its lighter congener cerium. All but two elements up to bismuth (element 83) have an isotope that is practically stable for all purposes (""classically stable""), with the exceptions being technetium and promethium (elements 43 and 61). All elements from polonium (element 84) onward are measurably radioactive. Th is one of the three nuclides beyond bismuth (the other two being U and U) that have half-lives measured in billions of years; its"
"conditions. The fourth element, either actinium or lawrencium, has only radioactive isotopes. Actinium, which occurs only in trace amounts, continues the trend in chemical behavior for metals that form tripositive ions with a noble gas configuration; synthetic lawrencium is calculated and partially shown to be more similar to lutetium and yttrium. So far, no experiments have been conducted to synthesize any element that could be the next group 3 element. Unbiunium (Ubu), which could be considered a group 3 element if preceded by lanthanum and actinium, might be synthesized in the near future, it being only three spaces away from"
"Tritiated water Tritiated water is a radioactive form of water where the usual protium atoms are replaced with tritium. In its pure form it may be called tritium oxide (TO or HO) or super-heavy water. Pure TO is corrosive due to self-radiolysis. Diluted, tritiated water is mainly HO plus some HTO (HOH). It is also used as a tracer for water transport studies in life-science research. Furthermore, since it naturally occurs in minute quantities, it can be used to determine the age of various water-based liquids, such as vintage wines. The name ""super-heavy water"" helps distinguish the tritiated material from"
"of sources are known the measurement of this ratio for a sample of unknown origin can often be used to link it back to a certain source or production method. Protium or hydrogen-1, with one proton and no neutrons, is the most abundant element in the solar system, formed in the earliest rounds of stellar explosions after the Big Bang. After the universe exploded into life, the hot and dense cloud of particles began to cool, first forming subatomic particles like quarks and electrons, which then condensed to form protons and neutrons. Elements larger than hydrogen and helium were produced"
"Karnataka, India show that the biological half-life in the winter season is twice that of the summer season. Tritiated water Tritiated water is a radioactive form of water where the usual protium atoms are replaced with tritium. In its pure form it may be called tritium oxide (TO or HO) or super-heavy water. Pure TO is corrosive due to self-radiolysis. Diluted, tritiated water is mainly HO plus some HTO (HOH). It is also used as a tracer for water transport studies in life-science research. Furthermore, since it naturally occurs in minute quantities, it can be used to determine the age"
"Isotopes of technetium Technetium (Tc) is the first of the two elements lighter than bismuth that have no non-radioactive isotopes; the other such element is promethium. It is primarily artificial, with only trace quantities (About 16 thousand metric tonnes) existing in nature produced by spontaneous fission or neutron capture by molybdenum. The first isotopes to be synthesized were Tc and Tc in 1936, the first artificial element to be produced. The most stable radioisotopes are Tc (half-life of 4.21 million years), Tc (half-life: 4.2 million years) and Tc (half-life: 211,100 years). Thirty-three other radioisotopes have been characterized with atomic masses"
"more pairs of protons have appreciable short-range nuclear force attractions. For each element with atomic number Z small enough to occupy only the first three nuclear shells, that is up to that of calcium (Z = 20), there exists a stable isotope with N/Z ratio of one, with the exception of beryllium (N/Z = 1.25) and every element with odd atomic number between 9 and 19 inclusive (N = Z+1). Hydrogen-1 (N/Z ratio = 0) and helium-3 (N/Z ratio = 0.5) are the only stable isotopes with neutron–proton ratio under one. Uranium-238 and plutonium-244 have the highest N/Z ratios of"
"120.955 u (Pr) to 158.955 u (Pr). The primary decay mode before the stable isotope, Pr, is electron capture and the mode after is beta decay. The primary decay products before Pr are element 58 (cerium) isotopes and the primary products after are element 60 (neodymium) isotopes. Isotopes of praseodymium Naturally occurring praseodymium (Pr) is composed of one stable isotope, Pr. Thirty-eight radioisotopes have been characterized with the most stable being Pr, with a half-life of 13.57 days and Pr, with a half-life of 19.12 hours. All of the remaining radioactive isotopes have half-lives that are less than 5.985 hours"