The most common subnuclear particle, along with the proton. Protons and neutrons have very similar mass, but neutrons have no charge. High speed neutrons (energy 14.1 MeV) are the main product of DT fusion. As they have no charge they are not affected by the electron clouds of atoms, instead passing through them unaffected. This allows them to pass through matter easily and to enter the nuclei of atoms, where they can cause transmutation into other elements. These newly created elements can be radioactive; management of this effect and the activated vessel materials is an important safety concern for tokamaks.