Achievements of neutron science

Starting from basic physical investigations into antiferromagnetism in insulators and rare earth metals, the range of disciplines utilising neutron scattering has expanded far beyond the initial expectations for the technique.

Magnetic Structures
Almost everything we know about magnetic structure – from the early demonstration of anti-ferromagnetism in simple systems (Shull, Nobel prize 1994), to the complex magnetic structures being developed by hard magnets – has come from experiments with neutrons. Similarly, polarised neutron reflectometry provides unique access to the surface and interface magnetism in thin films and multilayers.

Elementary Excitations and Phase Transitions
Similarly, nearly all our knowledge of elementary excitations such as phonons or magnons in crystalline solids, and their relationships to 2nd order phase transitions, stems from inelastic neutron scattering (Brockhouse, Nobel prize 1994).

Polymer Conformation and Dynamics
Neutrons have provided the most direct information on polymer conformation and the associated scaling laws, and polymer dynamics such as reptation, corroborating the Nobel prize winning theoretical concepts of Flory (1974) and DeGennes (1991).

Structure and Dynamics of Liquids
Neutrons have provided much of our basic understanding of the structure and dynamics of liquids. The results have had a major influence on theoretical developments such as memory function formalism, or mode coupling theory for description of the glass transition, and the development of computer simulation techniques now used widely from fundamental physics and chemistry
to biology.

Proton Positions and Motions in Biomolecules
Neutrons have determined water organisation in proteins and other biological systems and function critical hydrogen positions in enzymes. Inelastic neutron scattering led to a characterisation of large amplitude internal motions in small proteins, and of a dynamical transition that is correlated with function. Neutron studies on lipid membranes have provided the basis for our present view of the bilayer as a dynamically rough and extremely soft surface.

Crystal Structures and Magnetism of High Temperature Superconductors
Neutrons have provided the definitive crystal structures of high temperature superconductors, which serve as the basis for all considerations of the mechanism of superconductivity and have led to production of better quality materials. Neutron spectroscopy has provided unique information on the nature of magnetism in high temperature superconductors, on the interplay between magnetic fluctuations and superconductivity and on the role of the lattice dynamics.

Concepts of Statistical Physics
Neutrons have made major contributions to our understanding of model systems for statistical physics in one, two and three dimensions, including verification of the Haldane conjecture, determination of the properties of the Haldane gap, and the discovery of solitons as the characteristic elementary excitation of strongly non-linear magnetic systems.

Strain in Engineering Materials
Neutron strain measurement on engineering materials has made an important contribution to our knowledge of residual stresses. These stresses are essential to making reliable estimates of component life times. Important work has been carried out on welded structures, in particular the method is accelerating the introduction of new friction based welding techniques. Often post weld heat treatment is needed to reduce potentially life time threatening residual stresses; neutron diffraction has improved their definition. 

Electro-weak Interaction
Neutron decay experiments made essential contributions to the understanding of the „weak interaction“ and the unification of the electromagnetic and weak interaction to the „electro-weak interaction”. Parity nonconservation has been shown for the neutron decay, and neutron decay data also contributed to fixing the number of lepton families as three. 

Quantisation of Neutron Waves in the Field of Gravity
Four hundred years after Galilei neutron physicists observed the quantisation of ultra-cold neutrons in the gravity field and the quantisation of thermal neutrons due to confinement.

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