The neutron is a subatomic particle, symbol
n
or
n0
, which has no electric charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave similarly within the nucleus, they are both referred to as nucleons. Nucleons have a mass of approximately one atomic mass unit, or dalton. Their properties and interactions are described by nuclear physics. Protons and neutrons are not elementary particles; each is composed of three quarks.
In nuclear physics, the island of stability is a predicted set of isotopes of superheavy elements that may have considerably longer half-lives than known isotopes of these elements. It is predicted to appear as an "island" in the chart of nuclides, separated from known stable and long-lived primordial radionuclides. Its theoretical existence is attributed to stabilizing effects of predicted "magic numbers" of protons and neutrons in the superheavy mass region.
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.
Samuel Chao Chung Ting is an American physicist who, with Burton Richter, received the Nobel Prize in 1976 for discovering the subatomic J/ψ particle.
In nuclear astrophysics, the rapid neutron-capture process, also known as the r-process, is a set of nuclear reactions that is responsible for the creation of approximately half of the atomic nuclei heavier than iron, the "heavy elements", with the other half produced by the p-process and s-process. The r-process usually synthesizes the most neutron-rich stable isotopes of each heavy element. The r-process can typically synthesize the heaviest four isotopes of every heavy element; of these, the heavier two are called r-only nuclei because they are created exclusively via the r-process. Abundance peaks for the r-process occur near mass numbers A = 82, A = 130 and A = 196.
The Kamioka Liquid Scintillator Antineutrino Detector (KamLAND) is an electron antineutrino detector at the Kamioka Observatory, an underground neutrino detection facility in Hida, Gifu, Japan. The device is situated in a drift mine shaft in the old KamiokaNDE cavity in the Japanese Alps. Although located in the Kamioka Observatory, which is part of the University of Tokyo, this project is conducted by a team at Tohoku University. The site is surrounded by 53 Japanese commercial nuclear reactors. Nuclear reactors produce electron antineutrinos () during the decay of radioactive fission products in the nuclear fuel. Like the intensity of light from a light bulb or a distant star, the isotropically-emitted flux decreases at 1/R2 per increasing distance R from the reactor. The device is sensitive up to an estimated 25% of antineutrinos from nuclear reactors that exceed the threshold energy of 1.8 megaelectronvolts (MeV) and thus produces a signal in the detector.
Uranium (92U) is a naturally occurring radioactive element (radioelement) with no stable isotopes. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in Earth's crust. The decay product uranium-234 is also found. Other isotopes such as uranium-233 have been produced in breeder reactors. In addition to isotopes found in nature or nuclear reactors, many isotopes with far shorter half-lives have been produced, ranging from 214U to 242U. The standard atomic weight of natural uranium is 238.02891(3).
Naturally occurring xenon (54Xe) consists of seven stable isotopes and two very long-lived isotopes. Double electron capture has been observed in 124Xe and double beta decay in 136Xe, which are among the longest measured half-lives of all nuclides. The isotopes 126Xe and 134Xe are also predicted to undergo double beta decay, but this process has never been observed in these isotopes, so they are considered to be stable. Beyond these stable forms, 32 artificial unstable isotopes and various isomers have been studied, the longest-lived of which is 127Xe with a half-life of 36.345 days. All other isotopes have half-lives less than 12 days, most less than 20 hours. The shortest-lived isotope, 108Xe, has a half-life of 58 μs, and is the heaviest known nuclide with equal numbers of protons and neutrons. Of known isomers, the longest-lived is 131mXe with a half-life of 11.934 days. 129Xe is produced by beta decay of 129I ; 131mXe, 133Xe, 133mXe, and 135Xe are some of the fission products of both 235U and 239Pu, so are used as indicators of nuclear explosions.
Helium (2He) has nine known isotopes, but only helium-3 (3He) and helium-4 (4He) are stable. All radioisotopes are short-lived; the longest-lived is 6He with half-life 806.92(24) milliseconds. The least stable is 10He, with half-life 260(40) yoctoseconds, though 2He may have an even shorter half-life.
The Daya Bay Reactor Neutrino Experiment is a China-based multinational particle physics project studying neutrinos, in particular neutrino oscillations. The multinational collaboration includes researchers from China, Chile, the United States, Taiwan, Russia, and the Czech Republic. The US side of the project is funded by the US Department of Energy's Office of High Energy Physics.
Main Injector Experiment for ν-A, or MINERνA, is a neutrino scattering experiment which uses the NuMI beamline at Fermilab. MINERνA seeks to measure low energy neutrino interactions both in support of neutrino oscillation experiments and also to study the strong dynamics of the nucleon and nucleus that affect these interactions.
Ultracold neutrons (UCN) are free neutrons which can be stored in traps made from certain materials. The storage is based on the reflection of UCN by such materials under any angle of incidence.
The chameleon is a hypothetical scalar particle that couples to matter more weakly than gravity, postulated as a dark energy candidate. Due to a non-linear self-interaction, it has a variable effective mass which is an increasing function of the ambient energy density—as a result, the range of the force mediated by the particle is predicted to be very small in regions of high density but much larger in low-density intergalactic regions: out in the cosmos chameleon models permit a range of up to several thousand parsecs. As a result of this variable mass, the hypothetical fifth force mediated by the chameleon is able to evade current constraints on equivalence principle violation derived from terrestrial experiments even if it couples to matter with a strength equal or greater than that of gravity. Although this property would allow the chameleon to drive the currently observed acceleration of the universe's expansion, it also makes it very difficult to test for experimentally.
Borexino is a deep underground particle physics experiment to study low energy (sub-MeV) solar neutrinos. The detector is the world's most radio-pure liquid scintillator calorimeter and is protected by 3,800 meters of water-equivalent depth. The scintillator is pseudocumene and PPO which is held in place by a thin nylon sphere. It is placed within a stainless steel sphere which holds the photomultiplier tubes (PMTs) used as signal detectors and is shielded by a water tank to protect it against external radiation. Outward pointing PMT's look for any outward facing light flashes to tag incoming cosmic muons that manage to penetrate the overburden of the mountain above. Neutrino energy can be determined through the number of photoelectrons measured in the PMT's. While the position can be determined by extrapolating the difference in arrival times of photons at PMT's throughout the chamber.
The nuclear drip line is the boundary beyond which atomic nuclei are unbound with respect to the emission of a proton or neutron.
Double Chooz was a short-baseline neutrino oscillation experiment in Chooz, France. Its goal was to measure or set a limit on the θ13 mixing angle, a neutrino oscillation parameter responsible for changing electron neutrinos into other neutrinos. The experiment used the Chooz Nuclear Power Plant reactors as a neutrino source and measured the flux of neutrinos from them. To accomplish this, Double Chooz had a set of two detectors situated 400 meters and 1050 meters from the reactors. Double Chooz was a successor to the Chooz experiment; one of its detectors occupies the same site as its predecessor. Until January 2015 all data had been collected using only the far detector. The near detector was completed in September 2014, after construction delays, and started taking data at the beginning of 2015. Both detectors stopped taking data in late December 2017.
Radiation materials science is a subfield of materials science which studies the interaction of radiation with matter: a broad subject covering many forms of irradiation and of matter.
The Widom–Larsen theory is a proposed explanation for supposed Low Energy Nuclear Reactions (LENR) developed in 2005 by Allan Widom and Lewis Larsen. In the paper describing the idea, they claim that ultra low momentum neutrons are produced in the cold fusion apparatuses during weak interactions when protons capture "heavy" electrons from metallic hydride surfaces. One source has held that it is "unlikely the electron energy threshold for neutron production can be reached in a metal lattice system without a substantial energy input".
The STEREO experiment investigated the possible oscillation of neutrinos from a nuclear reactor into light so-called sterile neutrinos. It was located at the Institut Laue–Langevin (ILL) in Grenoble, France. The experiment took data from November 2016 to November 2020. The final results of the experiment rejected the hypothesis of a light sterile neutrino.
Blayne Ryan Heckel is an American experimental physicist whose research involved precision measurements in atomic physics and gravitational physics. He is a professor emeritus at the University of Washington in Seattle.
