page_title: Nuclear force
hierarchical_section_title: Nuclear force
caption_attribution_description: English: Potential energy of the 1S0 state of the nuclear force as computed according to equations by Reid, R.V. (1968). "Local phenomenological nuclean-nucleon potentials". Annals of Physics 50: 411–448.
context_page_description: The nuclear force is a force that acts between the protons and neutrons of atoms. Neutrons and protons, both nucleons, are affected by the nuclear force almost identically. Since protons have charge +1 e, they experience an electric force that tends to push them apart, but at short range the attractive nuclear force is strong enough to overcome the electromagnetic force. The nuclear force binds nucleons into atomic nuclei.
  The nuclear force is powerfully attractive between nucleons at distances of about 1 femtometre, but it rapidly decreases to insignificance at distances beyond about 2.5 fm. At distances less than 0.7 fm, the nuclear force becomes repulsive. This repulsive component is responsible for the physical size of nuclei, since the nucleons can come no closer than the force allows. By comparison, the size of an atom, measured in angstroms, is five orders of magnitude larger. The nuclear force is not simple, however, since it depends on the nucleon spins, has a tensor component, and may depend on the relative momentum of the nucleons.
  The nuclear force plays an essential role in storing energy that is used in nuclear power and nuclear weapons.
context_section_description: The nuclear force (or nucleon–nucleon interaction or residual strong force) is a force that acts between the protons and neutrons of atoms. Neutrons and protons, both nucleons, are affected by the nuclear force almost identically. Since protons have charge +1 e, they experience an electric force that tends to push them apart, but at short range the attractive nuclear force is strong enough to overcome the electromagnetic force.  The nuclear force binds nucleons into atomic nuclei.
  The nuclear force is powerfully attractive between nucleons at distances of about 1 femtometre (fm, or 1.0 × 10⁻¹⁵ metres), but it rapidly decreases to insignificance at distances beyond about 2.5 fm. At distances less than 0.7 fm, the nuclear force becomes repulsive. This repulsive component is responsible for the physical size of nuclei, since the nucleons can come no closer than the force allows. By comparison, the size of an atom, measured in angstroms (Å, or 1.0 × 10⁻¹⁰ m), is five orders of magnitude larger. The nuclear force is not simple, however, since it depends on the nucleon spins, has a tensor component, and may depend on the relative momentum of the nucleons.
  The nuclear force plays an essential role in storing energy that is used in nuclear power and nuclear weapons.  Work (energy) is required to bring charged protons together against their electric repulsion.  This energy is stored when the protons and neutrons are bound together by the nuclear force to form a nucleus.  The mass of a nucleus is less than the sum total of the individual masses of the protons and neutrons.  The difference in masses is known as the mass defect, which can be expressed as an energy equivalent. Energy is released when a heavy nucleus breaks apart into two or more lighter nuclei.  This energy is the electromagnetic potential energy that is released when the nuclear force no longer holds the charged nuclear fragments together.
  A quantitative description of the nuclear force relies on equations that are partly empirical.  These equations model the internucleon potential energies, or potentials. (Generally, forces within a system of particles can be more simply modeled by describing the system's potential energy; the negative gradient of a potential is equal to the vector force.) The constants for the equations are phenomenological, that is, determined by fitting the equations to experimental data. The internucleon potentials attempt to describe the properties of nucleon–nucleon interaction. Once determined, any given potential can be used in, e.g., the Schrödinger equation to determine the quantum mechanical properties of the nucleon system.
  The discovery of the neutron in 1932 revealed that atomic nuclei were made of protons and neutrons, held together by an attractive force. By 1935 the nuclear force was conceived to be transmitted by particles called mesons. This theoretical development included a description of the Yukawa potential, an early example of a nuclear potential. Pions, fulfilling the prediction, were discovered experimentally in 1947. By the 1970s, the quark model had been developed, by which the mesons and nucleons were viewed as composed of quarks and gluons. By this new model, the nuclear force, resulting from the exchange of mesons between neighboring nucleons, is a residual effect of the strong force.The general formula for the force between one collection of n1 nucleons and another of n2 nucleons is
  F=[-H{e^(-d/d0)}n1n2]÷d^2
caption: Corresponding potential energy (in units of MeV) of two nucleons as a function of distance as computed from the Reid potential. The potential well is a minimum at a distance of about 0.8 fm. With this potential nucleons can become bound with a negative "binding energy."
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