Why Neutrons?

What Is a Neutron?

Data for a model showing peptides inserting themselves in holes they form in a cell membrane

Data produced data for a model that shows peptides (cylinders) inserting themselves in holes they form in a cell membrane.

A neutron is one of the fundamental particles that make up matter. This uncharged particle exists in the nucleus of a typical atom, along with its positively charged counterpart, the proton. Protons and neutrons each have about the same mass, and both can exist as free particles away from the nucleus. In the universe, neutrons are abundant, making up more than half of all visible matter.

What are Some Properties of Neutrons?

Neutrons have many properties that make them ideal for certain types of research. Because of their unique sensitivity to hydrogen, neutrons can be used to precisely locate hydrogen atoms, enabling a more accurate determination of molecular structure, which is important for the design of new therapeutic drugs. Neutrons scattered from hydrogen in water can locate bits of moisture in fighter jet wings—signs of microscopic cracking and early corrosion that pinpoint the part of the wing that should be replaced.

Atomic model of yttrium-barium-copper oxide

Atomic model of yttrium-barium-copper oxide, a superconducting ceramic whose oxygen positions were determined by neutron scattering.

Besides hydrogen, neutrons can locate other light atoms among heavy atoms. This capability allowed scientists to determine the critical positions of light oxygen atoms in yttrium-barium-copper oxide (YBCO), a promising high-temperature, superconducting ceramic. YBCO wires may someday be used to increase the energy efficiency of electric motors, generators, transmission lines, transformers, and magnet-containing devices, such as particle accelerators for research, medical diagnostic machines, and levitated, high-speed trains.

A neutron acts like a tiny bar magnet that points like a compass needle; the size and direction of this magnetization is called a magnetic moment. Beams of "polarized neutrons" whose moments all point in the same direction can be created. Such beams allow scientists to probe properties of magnetic materials (like those on your credit card or in compact discs) and measure fluctuations in magnetic fields penetrating and produced by superconductors.

Because the energies of thermal neutrons almost match the energies of atoms in motion, neutrons can be used to track molecular vibrations, movements of atoms during catalytic reactions, and changes in the behavior of materials subjected to outside forces, such as rising temperature, pressure, or magnetic field strength.

Properties of Neutrons

Nobel Laureate Clifford Shull

Nobel Laureate Clifford Shull was among the ORNL researchers who pioneered neutron scattering by using neutrons from the Laboratory's Graphite Reactor.

  • Neutrons are NEUTRAL particles. They
    • are highly penetrating,
    • can be used as nondestructive probes, and
    • can be used to study samples in severe environments
  • Neutrons have a MAGNETIC moment. They can be used to
    • study microscopic magnetic structure,
    • study magnetic fluctuations, and
    • develop magnetic materials
  • Neutrons have SPIN. They can be
    • formed into polarized neutron beams,
    • used to study nuclear (atomic) orientation, and
    • used for coherent and incoherent scattering.
  • The ENERGIES of thermal neutrons are similar to the energies of elementary excitations in solids. Both have similar
    • molecular vibrations,
    • lattice modes, and
    • dynamics of atomic motion.
  • The WAVELENGTHS of neutrons are similar to atomic spacings. They can determine
    • structural sensitivity,
    • structural information from 10-13 to 10-4 cm, and
    • crystal structures and atomic spacings.
  • Neutrons "see" NUCLEI. They
    • are sensitive to light atoms,
    • can exploit isotopic substitution, and
    • can use contrast variation to differentiate complex molecular structures.