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The nuclear force (or '''nucleon-nucleon interaction''' or '''residual strong force''') is the force between two or more Nucleon s. It is responsible for binding of Proton s and Neutron s into Atomic Nuclei . There has been a lot of work on understanding and parameterizing the nuclear force. The long-range part of this force is of the form of a Yukawa Potential due to the exchange of light mesons, such as the Pion s. Sometimes the nuclear force is called the residual strong force, in contrast to the Strong Interaction s which are now understood to arise from Quantum Chromodynamics (QCD). This phrasing was forced during the 1970s due to a change in paradigm. Before that time, the ''strong nuclear force'' referred to the inter-nucleon potential. After the introduction of the Quark Model , ''strong interaction'' came to mean QCD. Since nucleons have no Color Charge , the nuclear force does not directly involve the force carriers of Quantum Chromodynamics , the Gluon s. HISTORY The nuclear force has been at the heart of Nuclear Physics ever since the field was born in 1932 with the discovery of the Neutron by James Chadwick . The traditional goal of nuclear physics is to understand the properties of Atomic Nuclei in terms of the 'bare' interaction between pairs of nucleons, or nucleon-nucleon (''NN'') forces. The oldest attempt to explain the nature of the nuclear force is due to Hideki Yukawa . According to his theory, massive Boson s ( Meson s) mediate the interaction between two nucleons. Although, in light of QCD , meson theory is no longer perceived as fundamental, the meson-exchange concept (where Hadron s are treated as Elementary Particles ) continues to represent the best working model for a quantitative ''NN'' potential. Historically, it turned out to be a formidable task to describe the nuclear force just phenomenologically, and it took a quarter of a century to come up with the first semi-empirical quantitative models in the mid-1950s. Ever since, there has been substantial progress in experiment and theory related to the nuclear force. Most basic questions were settled in the 1960s and 1970s. In recent years, experimenters have concentrated on the subtleties of the nuclear force, such as its charge dependence, the precise value of the π''NN'' coupling constant, improved Phase Shift Analysis , high-precision ''NN'' data, high-precision ''NN'' potentials, ''NN'' scattering at intermediate and high energies, and attempts to derive the nuclear force from QCD. BASIC PROPERTIES OF THE NUCLEAR FORCE
NUCLEON-NUCLEON POTENTIALS Two-nucleon systems such as the Deuteron as well as proton-proton or neutron-proton scattering are ideal for studying the ''NN'' force. Such systems can be described by attributing a '' Potential '' (such as the Yukawa Potential ) to the nucleons and using the potentials in a Schrödinger Equation . The form of the potential is derived phenomenologically, although for the long-range interaction, meson-exchange theories help to construct the potential. The parameters of the potential are determined by fitting to experimental data such as the deuteron binding energy or ''NN'' Elastic Scattering Cross Section s (or, equivalently in this context, so-called ''NN'' Phase Shift s). The most widely used ''NN'' potentials are the Paris Potential , the Argonne AV18 Potential , the CD-Bonn Potential and the Nijmegen Potentials . FROM NUCLEONS TO NUCLEI The ultimate goal of Nuclear Physics would be to describe all Nuclear Interaction s from the basic interactions between nucleons. This is called the ''microscopic'' or ''ab initio'' approach of nuclear physics. There are two major obstacles to overcome before this dream can become reality:
However, thanks to the ongoing advances in computational resources, microscopic calculations directly producing Nuclear Shell Structure from two- and three-nucleon potentials have become feasible and have been attempted for nuclear masses up to A =12. A novel and promising approach is to develop Effective Field Theories for a consistent description of nucleon-nucleon and three-nucleon forces. In particular, Chiral Symmetry Breaking can be analysed in terms of an Effective Field Theory (called Chiral Perturbation Theory ) which allows Perturbative Calculation s of the interactions between nucleons with pions as exchange particles. NUCLEAR POTENTIALS A successful way of describing Nuclear Interaction s is to construct one potential for the whole nucleus instead of considering all its nucleon components. This is called the ''macroscopic'' approach. For example, scattering of neutrons from nuclei can be described by considering a plane wave in the potential of the nucleus, which comprises a real part and an imaginary part. This model is often called the optical model since it resembles the case of light scattered by an opaque glass sphere. Nuclear potentials can be ''local'' or ''global'': local potentials are limited to a narrow energy range and/or a narrow nuclear mass range, while global potentials, which have more parameters and are usually less accurate, are functions of the energy and the nuclear mass and can therefore be used in a wider range of applications. SEE ALSO REFERENCES
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