A Twist and a Spin
By cleverly manipulating two properties of a neutron beam, scientists at the National Institute of Standards and Technology (NIST) and their collaborators have created a powerful probe of materials that have complex and twisted magnetic structures.Penetrating deep inside heavyweight materials, yet still able to interact strongly with light elements, neutron beams image hydrogen-bearing liquids in engine parts, storage tanks and fuel cells. The beams can also map the shapes of polymers on the molecular scale, reveal the precise arrangement of atoms in a crystal and chart the distribution of water within growing plants. Neutron beams became even stronger probes when scientists learned how to harness two quantum properties of the beams. One of these properties, formally known as orbital angular momentum, or OAM, refers to the twisting, or rotational motion of a neutron as it travels forward, similar to the whirlpool formed by water as it travels down a drain. The other quantum property, spin, is related to the neutron’s magnetic field, and can be likened to the spinning motion of a top.