Protonu

Protonu, known in English as the proton, is a subatomic particle that resides in atomic nuclei. It carries a positive electric charge equal in magnitude to the elementary charge and has a mass of about 1.6726 x 10^-27 kilograms (approximately 938 MeV/c^2). Its intrinsic angular momentum, or spin, is 1/2.

The proton is a baryon composed of three valence quarks: two up quarks and one down quark (uud). These quarks are bound by gluons via the strong interaction, described by quantum chromodynamics. The proton’s charge distribution yields a root-mean-square charge radius around 0.84 to 0.87 femtometers.

In atoms, protonu resides in the nucleus. The number of protons determines the atomic number and thus the identity of the element, while protonu and neutrons together form the nucleus and are bound by the nuclear force. Protonu is extremely long-lived in ordinary matter; current experiments place a lower bound on its lifetime well beyond 10^34 years, though certain grand unified theories predict possible decay.

Discovery and development: Protonu was identified by Ernest Rutherford in studies of hydrogen nuclei around 1917–1919. The quark-model description of its internal structure emerged in the 1960s, supported by deep inelastic scattering experiments at SLAC.

Significance: Protonu underpins chemical identity and governs nuclear reactions, including the proton-proton chain that powers stars. It is a central subject in particle physics, cosmology, and applied science, including proton therapy in medicine.