Nuclear force

This article relates to the force called sometimes strong force residual . For the " nuclear force forte" , to see strong Interaction; for the " nuclear force faible" , to see weak Interaction. See also nuclear energy for its applications.

The nuclear force is a force which is exerted between Nucléon S. It is responsible for the connection of the Proton S and the Neutron S in the atomic nuclei. This force can be included/understood in light terms of exchange of Méson S, like the Pion S.

It is sometimes called strong force residual , to distinguish it from the strong Interaction which one now explains starting from the quantum Chromodynamique. This formulation was introduced into the years 1970 because of a change of Paradigme. Previously, the strong nuclear force indicated the force between nucleons. After the introduction of the Model of the quarks, the strong interaction indicated the force defined by the chromodynamic quantum one. The nucleons not having any Load of color, the nuclear force does not imply directly the Gluon S, particles responsible for the strong interaction.

History

The nuclear force is in the middle of the Nuclear physics since the birth of this discipline in 1932 with the discovery of the Neutron by James Chadwick. The traditional goal of the nuclear physics is to include/understand the properties of the Atomic nucleus in term of “naked” interactions between pairs of nucleons, or nucleon-nucleon forces ( NR ).

In 1935, Hideki Yukawa was the first to try to explain the nature of the nuclear force. According to its theory, Boson S solid masses (Meson S) are used mediators for the interaction between two nucleons. Although, in the light of the chromodynamic quantum one, the theory of mesons is not perceived any more like fundamental, the concept of exchange of mesons (in which the Hadron S are treated as elementary particles) always represents the best quantitative model for the potential NR .

Historically, the simple qualitative description of the nuclear force appeared a considerable task, and the construction of the semi-empirical quantitative model first in the middle of the years 1950 intervened only after one quarter century of research. Since then, of substantial progress intervened in the experimental and theoretical fields concerning the nuclear force. The majority of the fundamental questions were sliced in the years 1960 and 1970. More recently, the experimenters concentrated on the subtle aspects of the nuclear force, like the dependence of load, the precise determination of the constant of coupling π NR , the improvement of the analysis of the shift of phase, the measurement of utmost precision of the data and the potentials NR , the diffusion NR for intermediate and raised energies, and the attempts at description of the nuclear force from the chromodynamic quantum one.

Fundamental properties of the nuclear force

• the nuclear force is felt only by the Hadron S.
• With the typical distances from separation of the nucleons (1,3 Fm), it is a very intense gravitational attraction (104 newtons).
• At shorter distances, the force is strongly repulsive, which maintains a certain separation between nucleons.
• Beyond from approximately 1,3 Fm, the force decrease exponentially towards zero.
• At short distances, the nuclear force is more intense than the Coulomb force; it can overcome the repulsion between protons produced by the force of Coulomb inside the core. However, the force of Coulomb between protons has a greater range and becomes the only significant force between protons when they are separated of more than 2,5 Fm.
• the force NR is practically independent of nature of the nucleons, neutrons or protons. This property is called independence of load .
• the force NR depends on the fact that the Spin S of the nucleons are parallel or antiparallel.
• the force NR has a noncentral component or tensorial . This part of the force does not preserve the angular Orbital moment, which is a constant of the movement produced by a central Force.

Nucleon-nucleon potentials

The systems with two nucleons such as the deuteron or the diffusion proton-proton or neutron-proton are ideal to study the force NR . Such systems can be described by allotting a Potentiel (such as the Potentiel of Yukawa) to the nucleons and by using the potentials in a equation of Schrödinger. This method makes it possible to determine the form of the potential, although for the interactions with long range, the theories implying the exchanges of mesons facilitate construction of it. The parameters of the potential are determined by adaptation to the experimental data such as the binding energy of the deuteron or the cross sections of elastic Diffusion NR (or, in an equivalent way in this context, which one calls the shifts of phase NR ).

The potentials NR most usually used are in particular the Potentiel of Paris, the Potentiel Argonne AV18 and the Potentiel Cd-Bonn and the potential of Nijmegen.

Nucleons with the core

One could see in the Nuclear physics a goal ultime : to describe the whole of the nuclear interactions starting from the fundamental interactions between nucleons. It is what one calls the microscopic approach or ab.initio . Two major hurdles must however be surmounted before this dream does not become réalité :

• calculations in systems with several bodies are complex and require powerful means of calculation.

• It is proven that, in the systems with more than two nucleons, the forces with three bodies (and perhaps also forces with four bodies, five bodies, etc) play a significant part. Thus, the potentials with three nucleons (at least) must be included in the model.

However, thanks to increasing progress of the computing powers usable, microscopic calculations directly producing a Shell model starting from potentials with two or three nucleons became possible, and were tried for cores going until a Atomic mass equalizes to 12.

A new and very promising approach consists in developing effective theories for a coherent description of the nucleon-nucleon forces and forces with three nucleons. In particular, one little to analyze the Crack of chiral symmetry in terms of effective theory (called chiral Perturbation theory), which authorizes a calculation by disturbance interactions between nucleons, pawns being particles of exchange.

Nuclear potentials

A profitable way to describe the nuclear interactions consists in building a potential for the whole of the core, instead of examining the nucleons which compose it. This approach is known as macroscopic . For example, the neutron scattering by cores can be described by considering a plane wave in the potential of the core, consisted of a real part and an imaginary part. This model is often called the optical model by analogy with the phenomenon of diffusion of the light by an opaque sphere of glass.

The nuclear potentials can be local or total  : the local potentials are limited to a restricted field of energies and/or masses, whereas the total potentials, which have more parameters and are usually less precise, are a function of the energy and the mass of the core, and can thus be used in more a vast domain of applications.

Internal bonds

• nuclear Reaction
• Potential of Yukawa
• Nuclear energy

References

• Gerald Edward Brown and A.D. Jackson, Nucleon-nucleon The Interaction , (1976) North-Holland Publishing, Amsterdam ISBN 0-7204-0335-9
• R. Machleidt and I. Slaus, " Nucleon-nucleon The interaction" , J. Phys. G 27 (2001) R69 (topical review) .
• Kenneth S. Krane, " Introductory Nuclear Physics" , (1988) Wiley & Sounds ISBN 0-471-80553-X
• P. Navrátil and W.E. Ormand, " Ab.initio Shell model with has genuine three-nucleon forces for the p-Shell nuclei" , Phys. rev. C 68 , 034305 (2003).

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