Neutron Detector Can Identify Single Particles

The new neutron detector developed at the National Institute of Standards and Technology is able to measure individual neutrons and their intensities with a sensitivity at least a hundred times higher than that of the traditional neutron detectors. The detector works on the basis of a physical interaction known in the scientific community as Lyman alpha light, which is an electromagnetic emission of radiation located in the ultraviolet region of the optical spectrum.

Lyman alpha light emission occurs when helium-3 atoms absorb neutrons and decay into hydrogen atoms, emitting light in the process. Believe it or not, Lyman alpha radiation is in fact the most abundant form of light in the universe, since it is emitted by most average stars during nuclear fusion processes. We can neither see in the ultraviolet spectrum of light, nor experience ultraviolet light exposure in normal life, since ultraviolet radiation only travels a millimeter through air before being re-absorbed.

The Lyman alpha light was explained for the first time by Harvard physicist Theodore Lyman in 1906, who defined it as the emission of radiation occurring between the two lowest energy states of the hydrogen atom. As a neutron particle is being absorbed into the helium-3 atom, the nucleus becomes unstable and spontaneously disintegrates into two hydrogen atoms, tritium and hydrogen. The energy of the fission is converted into momentum, which accelerates the two at high speeds through the helium gas, thus emitting Lyman alpha radiation.

During the testing of the Lyman alpha radiation detector, or LAND, the NIST researchers have revealed that, for each absorbed neutron, 40 photons are being emitted in the helium gas, making it the most efficient neutron detector ever created, being able to measure not only multiple neutrons, but single neutrons as well.

Also, because it measures photons and not electrical charges, these detectors are much faster than their counterparts, which may routinely suffer from 'dead time,' i.e. longer periods of inactivity. NIST scientists hope to take the study even further and measure the electric dipole moment of the neutrons and maybe even their lifetime.