Neutron interferometer
Encyclopedia
In physics
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...

, a neutron interferometer is an interferometer capable of diffracting
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...

 neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...

s, allowing the wave-like nature of neutrons, and other related phenomena, to be explored.

Interferometry
Interferometry
Interferometry refers to a family of techniques in which electromagnetic waves are superimposed in order to extract information about the waves. An instrument used to interfere waves is called an interferometer. Interferometry is an important investigative technique in the fields of astronomy,...

 inherently depends on the wave nature of the object. As pointed out by de Broglie in his PhD thesis, particles, including neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...

s, can behave like waves (the so called wave-particle duality, now explained in the general framework of quantum mechanics
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...

). The wave functions of the individual interferometer paths are created and recombined coherently which needs the application of dynamical theory of diffraction
Dynamical theory of diffraction
The dynamical theory of diffraction describes the interaction of waves with a regular lattice. The wave fields traditionally described are X-rays, neutrons or electrons and the regular lattice, atomic crystal structures or nanometer scaled multi-layers or self arranged systems...

. Neutron interferometers are the counterpart of X-ray interferometer
X-ray interferometer
An X-ray interferometer is analogous to a neutron interferometer. It has been suggested that it may offer the very highest spatial resolution in astronomy, though the technology is unproven as of 2008....

s and are used to study quantities or benefits related to thermal neutron radiation
Neutron radiation
Neutron radiation is a kind of ionizing radiation which consists of free neutrons. A result of nuclear fission or nuclear fusion, it consists of the release of free neutrons from atoms, and these free neutrons react with nuclei of other atoms to form new isotopes, which, in turn, may produce...

.

Neutron interferometers are used to determine minute quantum-mechanical effects to the neutron wave, such as studies of the
  • Aharonov–Bohm effect
  • gravity acting on an elementary particle, the neutron
  • rotation of the earth acting on a quantum system

they can be applied for
  • neutron phase imaging
  • tests of the dynamical theory of diffraction
    Dynamical theory of diffraction
    The dynamical theory of diffraction describes the interaction of waves with a regular lattice. The wave fields traditionally described are X-rays, neutrons or electrons and the regular lattice, atomic crystal structures or nanometer scaled multi-layers or self arranged systems...



Like X-ray interferometer
X-ray interferometer
An X-ray interferometer is analogous to a neutron interferometer. It has been suggested that it may offer the very highest spatial resolution in astronomy, though the technology is unproven as of 2008....

s, neutron interferometers are typically made from a single large crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...

 of silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

, often 10 to 30 or more centimeters in diameter and 20 to 60 cm or more in length. Modern semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

 technology allows large single-crystal silicon boules
Boule (crystal)
A boule is a single-crystal ingot produced by synthetic means. A boule of silicon is the starting material for most of the integrated circuits used today....

 to be easily grown. Since the boule is a single crystal, the atoms in the boule are precisely aligned, to within small fractions of a nanometer or an angstrom
Ångström
The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....

, over the entire boule. The interferometer is created by removing all but three slices of silicon, held in perfect alignment by a base. (image) Neutrons impinge on the first slice, where, by diffraction
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...

 from the crystalline lattice
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...

, they separate into two beams. At the second slice, they are diffracted again, with two beams continuing on to the third slice. At the third slice, the beams recombine, interfering constructively or destructively, completing the interferometer. Without the precise, angstrom-level alignment of the three slices, the interference results would not be meaningful.

Only recently, a neutron interferometer for cold and ultracold neutrons was designed and successfully run. Neutron-optical components in this case comprise three gratings. They are artificially holographically produced, i.e., by means of a light-optic two-wave interference setup illuminating a photo-neutron-refractive polymer.
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