The neutron is a subatomic particle with no net electric charge and a mass of 939.573 MeV/c² (slightly more than a proton). Its spin is ½. Its antiparticle is called the antineutron. The neutron and proton are instances of a nucleon.
The nucleus of most atoms (all except the most common isotope of hydrogen, protium, which consists of a single proton only) consists of protons and neutrons.
The neutron plays an important role in many nuclear reactions. For example, neutron capture often results in neutron activation, inducing radioactivity. In particular, knowledge of neutrons and their behavior has been important in the development of nuclear reactors and nuclear weapons.
The development of "neutron lenses" based on total internal reflection within hollow glass capillary tubes or by reflection from dimpled aluminum plates has driven ongoing research into neutron microscopy and neutron/gamma ray tomography.
One use of neutron emitters is the detection of light nuclei, particularly the hydrogen found in water molecules. When a fast neutron collides with a light nucleus, it loses a large fraction of its energy. By measuring the rate at which slow neutrons return to the probe after reflecting off of hydrogen nuclei, a neutron probe may determine the water content in soil.
Pure neutron radiation is used as an anti-organics weapon in Neutron Beams. Neutron flux is deadly in a manner similar to gamma radiation. However, neutrons do not lose energy when they ionize atoms; they are chargeless, thus can pass through most sorts of electromagnetic fields (energy shielding) and armor materials with relative ease. The only exception would be exceptionally thick and atomically heavy materials, like starship hulls.