A proton is an elementary, subatomic particle with symbol “p or p+” and having one positive electrical charge. Protons are present in the nuclei of atoms. The nucleus of every atom constitutes one or more protons. The proton is responsible for the positive charge of the nucleus. Protons are very small and can only be seen with an electron microscope. In year 1920, Ernest Rutherford was able to extract hydrogen nucleus from the nuclei of nitrogen by collision. So, he named hydrogen nucleus as proton.

The number of protons present in the nucleus of an atom makes up the atomic number and each element has its own distinct atomic number. Here are some basic facts about protons:

• The proton possesses mass which is about 1,840 times the mass of the electron and somewhat less than the mass of the neutron. The mass number of the nucleus constitutes total number of nucleons held by it (i.e. protons and neutrons, collectively).
• Before the Big Bang, all the energy in the universe was travelling freely in the form of large photon like particles called bosons which had tons of energy. These bosons got broken apart into protons and anti-protons. Most of these protons and anti-protons lost their energy and formed themselves back into bosons again and some of the anti-photons got disappeared in the universe. So, all the mass in this universe is due to these remaining protons.
• The number of protons that makes up the nucleus of an atom tells the chemical element to which the atom belongs. So, a helium atom, a gold atom or an oxygen atom are differentiated on the basis of number of protons they have and this number is their atomic number. For example, the atomic number of chlorine is 17, which means each chlorine atom contains 17 protons and each atom which has 17 protons is a chlorine atom.
• Proton is the lightest of all the elementary particles. They are made up of three quarks – one up quark and two down quarks. A strong nuclear force binds the quarks together. This nuclear force makes up the mass of the protons. The current quark mass refers to the mass of the quark by itself while the constituent quark mass is the current quark mass plus the mass of the gluon particle field surrounding the quark. Gluons bind the current quarks together and they constitute most of the proton’s mass.
• The free proton is considered to be stable particle and it does not break down by itself to other particles.
• Protons have an affinity for electrons but in environments with high energies or temperatures, they get separated from electrons naturally and are held free.
• Protons possess a charge which is equal but opposite to the charge on electrons.
• The charge radius of proton is 0.8768 femtometre which is about 25000 times less than the mean radius of a hydrogen atom.
• The antiproton is an anti-particle of proton which was discovered in 1955. It carries the same mass as the proton but a unit negative charge and opposite magnetic moment.
• The radioactive decay of unstable free neutrons leads to the formation of protons.
• As per the recent experimental evidence, the proton is known to have a finite lifetime of at least 10³¹ years.
• Free hydrogen atoms react with each other to form neutral hydrogen molecules (H2) which act as an easy source of protons for accelerators and other hadrons physics experiments which need the protons to accelerate as in large hadrons collider.
• According to the Apollo Lunar Surface Experiments Package (ALSEP), more than 95% of the particles found in the solar wind comprise electrons and protons, equally.