Neutron interferometer

In physics, a neutron interferometer is an interferometer capable of diffracting neutrons, allowing the wave-like nature of neutrons, and other related phenomena, to be explored.

Interferometry inherently depends on the wave nature of the object. As pointed out by de Broglie in his PhD-thesis, particles, including neutrons, can behave like waves (the so called Wave-particle duality, now explained in the general framework of quantum mechanics). Since free neutrons only live about 11 minutes, experiments need to be carried out near a neutron source, usually a nuclear power plant. Since neutrons react only very slightly to electromagnetic forces, special optics is required, nevertheless many experiments were carried out, especially in the 1960s.

Neutron interferometers are typically carved from a single large crystal of silicon, often 10 to 30 or more centimeters in diameter and 20 to 60 or more in length. Modern semiconductor technology allows large single-crystal silicon boules to be easily grown. Since the boule is a single crystal, the atoms in the boule are precisely aligned, to within small fractions of an angstrom, over the entire boule. The interferometer is created by carving away all but three slices of silicon, held in perfect alignment by a base. Neutrons impinge on the first slice, where, by diffraction from the crystalline lattice, 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.

References

V. F. Sears, Neutron Optics, Oxford University Press (1998).