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A chemical element is a chemical substance that cannot be broken down into other substances by chemical reactions. The basic particle that constitutes a chemical element is the atom. Chemical elements are identified by the number of protons in the nuclei of their atoms, known as the element's atomic number. For example, oxygen has an atomic number of 8, meaning that each oxygen atom has 8 protons in its nucleus. Two or more atoms of the same element can combine to form molecules, in contrast to chemical compounds or mixtures, which contain atoms of different elements. Atoms can be transformed into different elements in nuclear reactions, which change an atom's atomic number.
Stable nuclides are nuclides that are not radioactive and so do not spontaneously undergo radioactive decay. When such nuclides are referred to in relation to specific elements, they are usually termed stable isotopes.
In physical cosmology, Big Bang nucleosynthesis is the production of nuclei other than those of the lightest isotope of hydrogen during the early phases of the universe. This type of nucleosynthesis is thought by most cosmologists to have occurred from 10 seconds to 20 minutes after the Big Bang. It is thought to be responsible for the formation of most of the universe's helium, along with small fractions of the hydrogen isotope deuterium, the helium isotope helium-3 (3He), and a very small fraction of the lithium isotope lithium-7 (7Li). In addition to these stable nuclei, two unstable or radioactive isotopes were produced: the heavy hydrogen isotope tritium and the beryllium isotope beryllium-7 (7Be). These unstable isotopes later decayed into 3He and 7Li, respectively, as above.
Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in a process called Big Bang nucleosynthesis. After about 20 minutes, the universe had expanded and cooled to a point at which these high-energy collisions among nucleons ended, so only the fastest and simplest reactions occurred, leaving our universe containing hydrogen and helium. The rest is traces of other elements such as lithium and the hydrogen isotope deuterium. Nucleosynthesis in stars and their explosions later produced the variety of elements and isotopes that we have today, in a process called cosmic chemical evolution. The amounts of total mass in elements heavier than hydrogen and helium remains small, so that the universe still has approximately the same composition.
A nuclide is a class of atoms characterized by their number of protons, Z, their number of neutrons, N, and their nuclear energy state.
The abundance of the chemical elements is a measure of the occurrence of the chemical elements relative to all other elements in a given environment. Abundance is measured in one of three ways: by mass fraction, by mole fraction, or by volume fraction. Volume fraction is a common abundance measure in mixed gases such as planetary atmospheres, and is similar in value to molecular mole fraction for gas mixtures at relatively low densities and pressures, and ideal gas mixtures. Most abundance values in this article are given as mass fractions.
Spallation is a process in which fragments of material (spall) are ejected from a body due to impact or stress. In the context of impact mechanics it describes ejection of material from a target during impact by a projectile. In planetary physics, spallation describes meteoritic impacts on a planetary surface and the effects of stellar winds and cosmic rays on planetary atmospheres and surfaces. In the context of mining or geology, spallation can refer to pieces of rock breaking off a rock face due to the internal stresses in the rock; it commonly occurs on mine shaft walls. In the context of anthropology, spallation is a process used to make stone tools such as arrowheads by knapping. In nuclear physics, spallation is the process in which a heavy nucleus emits numerous nucleons as a result of being hit by a high-energy particle, thus greatly reducing its atomic weight. In industrial processes and bioprocessing the loss of tubing material due to the repeated flexing of the tubing within a peristaltic pump is termed spallation.
Beryllium-10 (10Be) is a radioactive isotope of beryllium. It is formed in the Earth's atmosphere mainly by cosmic ray spallation of nitrogen and oxygen. Beryllium-10 has a half-life of 1.39 × 106 years, and decays by beta decay to stable boron-10 with a maximum energy of 556.2 keV. It decays through the reaction 10Be→10B + e−. Light elements in the atmosphere react with high energy galactic cosmic ray particles. The spallation of the reaction products is the source of 10Be (t, u particles like n or p):
The Oddo–Harkins rule holds that an element with an even atomic number is more abundant than the elements with immediately adjacent atomic numbers. For example, carbon, with atomic number 6, is more abundant than boron (5) and nitrogen (7). Generally, the relative abundance of an even atomic numbered element is roughly two orders of magnitude greater than the relative abundances of the immediately adjacent odd atomic numbered elements to either side. This pattern was first reported by Giuseppe Oddo in 1914 and William Draper Harkins in 1917. The Oddo-Harkins rule is true for all elements beginning with carbon produced by stellar nucleosynthesis but not true for the lightest elements below carbon produced by big bang nucleosynthesis and cosmic ray spallation.
Cosmic ray spallation, also known as the x-process, is a set of naturally occurring nuclear reactions causing nucleosynthesis; it refers to the formation of chemical elements from the impact of cosmic rays on an object. Cosmic rays are highly energetic charged particles from beyond Earth, ranging from protons, alpha particles, and nuclei of many heavier elements. About 1% of cosmic rays also consist of free electrons.
Beryllium (4Be) has 11 known isotopes and 3 known isomers, but only one of these isotopes is stable and a primordial nuclide. As such, beryllium is considered a monoisotopic element. It is also a mononuclidic element, because its other isotopes have such short half-lives that none are primordial and their abundance is very low. Beryllium is unique as being the only monoisotopic element with both an even number of protons and an odd number of neutrons. There are 25 other monoisotopic elements but all have odd atomic numbers, and even numbers of neutrons.
Chlorine-36 (36Cl) is an isotope of chlorine. Chlorine has two stable isotopes and one naturally occurring radioactive isotope, the cosmogenic isotope 36Cl. Its half-life is 301,300 ± 1,500 years. 36Cl decays primarily (98%) by beta-minus decay to 36Ar, and the balance to 36S.
A nucleogenic isotope, or nuclide, is one that is produced by a natural terrestrial nuclear reaction, other than a reaction beginning with cosmic rays. The nuclear reaction that produces nucleogenic nuclides is usually interaction with an alpha particle or the capture of fission or thermal neutrons. Some nucleogenic isotopes are stable and others are radioactive.
An extinct radionuclide is a radionuclide that was formed by nucleosynthesis before the formation of the Solar System, about 4.6 billion years ago, but has since decayed to virtually zero abundance and is no longer detectable as a primordial nuclide. Extinct radionuclides were generated by various processes in the early Solar system, and became part of the composition of meteorites and protoplanets. All widely documented extinct radionuclides have half-lives shorter than 100 million years.
Isotopes are distinct nuclear species of the same chemical element. They have the same atomic number and position in the periodic table, but differ in nucleon 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.
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.
Surface exposure dating is a collection of geochronological techniques for estimating the length of time that a rock has been exposed at or near Earth's surface. Surface exposure dating is used to date glacial advances and retreats, erosion history, lava flows, meteorite impacts, rock slides, fault scarps, cave development, and other geological events. It is most useful for rocks which have been exposed for between 103 and 106 years.
A radiogenic nuclide is a nuclide that is produced by a process of radioactive decay. It may itself be radioactive or stable.
Nuclear transmutation is the conversion of one chemical element or an isotope into another chemical element. Nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus of an atom is changed.
References
- 1 2 Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 13–15. ISBN 978-0-08-037941-8.
- ↑ "Beryllium | Properties, Uses, & Facts | Britannica". www.britannica.com. 2023-09-17. Retrieved 2023-10-19.
- ↑ Sapphire Lally (Jul 24, 2021). "How is gold made? The mysterious cosmic origins of heavy elements". New Scientist.
- ↑ SCOPE 50 - Radioecology after Chernobyl Archived 2014-05-13 at the Wayback Machine , the Scientific Committee on Problems of the Environment (SCOPE), 1993. See table 1.9 in Section 1.4.5.2.
- ↑ Schaefer, Joerg M.; Codilean, Alexandru T.; Willenbring, Jane K.; Lu, Zheng-Tian; Keisling, Benjamin; Fülöp, Réka-H.; Val, Pedro (2022-03-10). "Cosmogenic nuclide techniques". Nature Reviews Methods Primers. 2 (1): 1–22. doi:10.1038/s43586-022-00096-9. ISSN 2662-8449. S2CID 247396585.
- ↑ Lal, D.; Peters, B. (1967). "Cosmic Ray Produced Radioactivity on the Earth". Kosmische Strahlung II / Cosmic Rays II. Handbuch der Physik / Encyclopedia of Physics. Vol. 9 / 46 / 2. pp. 551–612. doi:10.1007/978-3-642-46079-1_7. ISBN 978-3-642-46081-4.
- ↑ Heisinger, B.; Lal, D.; Jull, A. J. T.; Kubik, P.; Ivy-Ochs, S.; Knie, K.; Nolte, E. (30 June 2002). "Production of selected cosmogenic radionuclides by muons: 2. Capture of negative muons". Earth and Planetary Science Letters. 200 (3): 357–369. Bibcode:2002E&PSL.200..357H. doi:10.1016/S0012-821X(02)00641-6.
- ↑ Dunne, Jeff; Elmore, David; Muzikar, Paul (1 February 1999). "Scaling factors for the rates of production of cosmogenic nuclides for geometric shielding and attenuation at depth on sloped surfaces". Geomorphology. 27 (1): 3–11. Bibcode:1999Geomo..27....3D. doi:10.1016/S0169-555X(98)00086-5.