Protonul

The proton is a positively charged baryon and a fundamental component of atomic nuclei. It has a rest mass of about 1.6726 × 10^-27 kilograms (approximately 938 MeV/c^2), a charge of +e, and an intrinsic spin of 1/2.

In the standard model, the proton is composed of three valence quarks—two up quarks and one down quark—along with a fluctuating sea of quark–antiquark pairs and gluons. The strong force, described by quantum chromodynamics, binds these constituents together. Much of the proton’s mass arises from the energy of these strong interactions rather than the masses of the quarks themselves.

The number of protons in a nucleus, called the atomic number Z, determines the identity of the element and its chemical properties. Protons and neutrons form the nucleus, held together by the strong force, while electrons are arranged around the nucleus by electromagnetic interactions.

Historically, the proton was identified in studies of the atomic nucleus in the early 20th century, and the term was coined by Ernest Rutherford. Experiments such as deep inelastic scattering in the mid-20th century revealed the proton’s substructure in terms of quarks and gluons.

Protons are highly stable under ordinary conditions; no definitive evidence of proton decay has been observed, with experimental lower bounds on the lifetime exceeding 10^34 years. The proton radius is about 0.84–0.88 femtometers, though precise measurements continue to refine this value and occasionally give rise to the so-called proton radius puzzle.