Physical world and mathematics

Neutron detection

Neutron detection is the indirect measurement of free neutrons, which carry no charge, using converter isotopes like helium-3, boron-10, and lithium-6 in gas-filled, scintillator, or semiconductor detectors.

Neutron diagnostics

Neutron diagnostics are the instruments in a fusion device that measure neutrons produced by fusion reactions, providing real-time measurement of fusion power, plasma ion temperature, and fast-ion behavior.

Neutron diffraction

Neutron diffraction is an experimental technique that scatters neutrons from a material's crystal lattice to determine atomic positions and magnetic order, locating light atoms like hydrogen that X-rays miss.

Neutron electric dipole moment

The neutron electric dipole moment (nEDM) measures charge separation along the neutron's spin axis. A nonzero value would signal new CP violation, but experiments have found none.

Neutron emission

Neutron emission is a nuclear decay or reaction process in which an atomic nucleus releases neutrons, whether promptly from excited fission fragments or after beta decay of neutron-rich nuclei.

Neutron halo

A neutron halo is an extended distribution of weakly bound neutrons around a nucleus's core, found near the neutron drip line and first seen in lithium-11.

Neutron imaging

Neutron imaging is a non-destructive technique that passes a neutron beam through an object to reveal internal structure and composition, complementing X-rays by detecting hydrogen, lithium, and isotopes.

Neutron interferometry

Neutron interferometry splits a beam of neutrons into coherent paths and recombines them, measuring phase shifts from gravity, magnetic fields, and nuclear interactions; first fringes were observed in 1974.

Neutron lifetime puzzle

The neutron lifetime puzzle is the long-standing, roughly 8.6-second discrepancy between beam experiments measuring the free neutron's lifetime near 888 seconds and bottle trap experiments near 878 seconds.

Neutron moderator

A neutron moderator is a material, such as light water, heavy water, or graphite, that slows fast fission neutrons in a reactor core, making further fission more likely.

Neutron poison

A neutron poison, also called a nuclear poison, is a non-fissionable substance that absorbs neutrons in a reactor core, adding negative reactivity to control fission.

Neutron radiation

Neutron radiation is ionizing radiation consisting of free neutrons, uncharged subatomic particles from fission and fusion. Neutrons penetrate deeply, are hard to shield, and can make objects radioactive.

Neutron radiography

Neutron radiography is an imaging technique that transmits a collimated neutron beam through an object; because neutrons interact with nuclei, light elements show strongly inside metals, unlike X-ray imaging.

Neutron reflectometry

Neutron reflectometry, also known as neutron reflectivity or neutron reflection, is a scattering technique measuring neutron reflection from flat surfaces and interfaces, probing buried layers, magnetic films, and solid–liquid boundaries.

Neutron research facilities

Neutron research facilities are large scientific installations that produce intense neutron beams in nuclear reactors or spallation sources, letting researchers study materials at the atomic scale.

Neutron scattering

Neutron scattering is a family of experimental techniques that directs free neutrons at a sample to determine atomic structure and dynamics, probing light elements where X-rays fail.

Neutron skin

A neutron skin is an excess of neutrons at the outer surface of a neutron-rich atomic nucleus, quantified as the difference between neutron and proton radii.

Neutron source

A neutron source is any device or material that emits neutrons, ranging from isotopic capsules to research reactors and particle accelerators used in well logging and materials science.

Neutron spectroscopy

Neutron spectroscopy measures the energy distribution of neutrons emitted by a source, used in fusion research to determine plasma ion temperature, fuel composition, and fast-ion velocity distributions.

Neutron spin echo

Neutron spin echo is a neutron scattering technique using Larmor precession to measure molecular motions, with the highest energy resolution of all neutron spectroscopy methods.

Neutron spin echo spectroscopy

Neutron spin echo spectroscopy is a neutron scattering technique that uses the Larmor precession of neutron spins as an internal clock to detect extremely small energy transfers.

Neutron star

A neutron star is the dense core left when a massive star collapses, crushing more than the Sun's mass into a city-sized sphere about 20 kilometers wide.

Neutron Star Interior Composition Explorer

NICER, the Neutron Star Interior Composition Explorer, is a NASA X-ray telescope mounted on the International Space Station in 2017 to measure neutron star masses and radii.

Neutron star merger

A neutron star merger is the collision of two neutron stars in a compact binary, emitting gravitational waves and producing a kilonova and heavy elements.

Neutron star–black hole merger

A neutron star–black hole merger (NSBH merger) is the coalescence of a binary with one neutron star and one stellar-mass black hole, first confirmed by gravitational waves from the events GW200105 and GW200115 in 2021.

Neutron superfluidity in Cassiopeia A

Neutron superfluidity in Cassiopeia A is the 2011 explanation for the unusually rapid cooling of the neutron star at the center of the Cassiopeia A supernova remnant.

Neutron-capture elements

Neutron-capture elements are the elements heavier than iron, built when atomic nuclei capture free neutrons in stars or explosive events, via the s-, r-, and i-processes.

Neutron-induced fission

Neutron-induced fission is the splitting of a heavy atomic nucleus after it absorbs a neutron, discovered by Otto Hahn and Fritz Strassmann in Berlin in 1938.

Nevado del Ruiz

Nevado del Ruiz, also known as Kumanday, is an active glacier-covered volcano in Colombia's Central Cordillera; its 1985 eruption sent lahars over Armero, killing more than 22,000 people.