neutroni

A neutron is a neutral baryon and one of the two main constituents of atomic nuclei, the other being the positively charged proton. It has spin 1/2 and is made of three quarks (two down quarks and one up quark) held together by gluons. Its rest mass is about 1.008665 atomic mass units (approximately 1.675 × 10−27 kilograms). The neutron carries no electric charge and has a small magnetic moment.

Free neutrons are unstable and decay by beta decay into a proton, an electron, and an antineutrino, with a mean lifetime of about 14.7 minutes. In bound nuclei, neutrons contribute to nuclear binding energy and the stability of the nucleus; whether a particular nucleus is stable depends on the balance of nuclear forces and energy.

Neutrons are produced in several ways, notably in nuclear fission and fusion reactions, and by spallation or certain (alpha,n) reactions. They interact with matter primarily through the strong nuclear force when close to nuclei, and via elastic and inelastic scattering. Because they are uncharged, neutrons can penetrate matter more readily than charged particles, though they are ultimately captured or scattered. Moderation with light-element materials (such as water or polyethylene) slows neutrons to thermal energies, where many isotopes have higher capture or fission probabilities.

Applications of neutrons are diverse. They are essential in nuclear reactors and in various neutron-source facilities, and they enable neutron scattering methods for studying the structure of materials. Neutron cross sections vary by isotope and energy, underpinning reactor control, imaging techniques, and analytical methods.

In astrophysics, neutrons are central to the physics of neutron stars and to nucleosynthesis processes such as the rapid neutron capture process (r-process), which builds heavy elements in explosive environments.