# Nuclear physics

The nuclear physics is the science which not seuleument studies the Atomic nucleus as such (development of an ideal model) but also the way in which it interacts when a particle arrives " with proximité" (the order of magnitude is 1E-12 cm, one usually speaks in nuclear physics about cross Section of which the unit is the Barn that is to say 1E-24 cm ²) core (obtaining experimental results). After a short historical background, this article is devoted to describe:

• the nuclear Structure , which aims at including/understanding how the Nucléon S (Proton S and Neutron S) interact to form the core.
• the mechanisms of the nuclear reactions of which the goal is to describe the various ways that have the cores to interact: fission, fusion, diffusion (elastic, inelastic), Radioactivity
• the scopes of application of the nuclear physics : Medicine with the Astrophysical , while passing by the production of energy, all these spheres of activity exploits the physics of the interactions radiation-matters.
• the research organizations in nuclear physics, France and in the world.

## Introduction

The matter consists of Molécule S, themselves consisted of Atome S. These atoms are made of a central core surrounded by an electronic cloud. The nuclear physics is the science which is interested in the whole of the physical phenomena utilizing the atomic nucleus. Because of the microscopic size of this one, the mathematical tools used primarily lie within the scope of the formalism of the quantum Mécanique.

The Atomic nucleus consists of Nucléon S, which is divided into Proton S and in Neutron S. the protons are particles which have a electric Charge elementary positive, whereas the neutrons are neutral particles. They have only one magnetic moment, and are thus only not very sensitive to the electromagnetic Champ, contrary to the protons. If one compared the atomic nucleus to a hard sphere, the ray of this sphere would be of some Fermi S, 1 Fermi being worth 10-15 meters (1 Fermi = 1 femtometer). Cores having the same value of Z, i.e. the same number of protons, and not having the same number of neutrons are called Isotope S.

## The core in the History

Until the turning of the 20th century, one believed that the Atome S were the ultimate components of the matter. The discovery of the Radioactivity in 1896 by Henri Becquerel and the studies which followed, in particular with the husbands Curie, started to suggest that the atoms were perhaps themselves of the made up objects. How, if not, the matter could it spontaneously emit particles as in the case of the radioactivity alpha?

It is into 1911 that Rutherford discovered that the Atomes seemed indeed to be made up objects. While analyzing the diffusion particles alpha emitted by a radioactive source through a gold sheet, it came from there to conclude that simplest seems to suppose that the atom contains a central load distributed in a very small volume (" it seems simplest to supposes that the atom contains has central charges distributed through has very small volume… " , Philosophical Magazine, Series 6, vol. 21, May 1911, p. 669-688). The model of Rutherford of the atom was thus a central core having an electric charge surrounded by electrons maintained in orbit by the electromagnetic interaction. He had already been proposed in 1904 by Nagaoka.

In 1919, Rutherford always discovers the existence in the core of the Proton, particle having an elementary positive load E , but having a mass much larger than that of the electron (which has a negative elementary electric charge to him). In 1932, Chadwick highlights the existence of the neutron, particle very similar to the proton, except the fact that it does not have an electric charge (from where its name). At the same period, Heisenberg proposes that the atomic nucleus is in fact made up of a unit of protons and neutrons.

## nuclear Structure

The strong Interaction maintains the cohesion of the nucleons within the core. It is most intense of the four fundamental forces of nature (from where its name). It characterizes by fact that it is strongly gravitational at short distance (when the nucleons approach very close one the other), repulsive with " moyenne" outdistance, and cancels itself with long distance. The protons being charged particles, they also interact via the Coulomb interaction. If the number of protons in the core is important, the latter takes the step on the strong interaction and the cores become unstable. The quantity of energy which ensures the cohesion of the core is called energy binding of the core.

## Nuclear reactions

A reaction is known as nuclear power when there is modification of the quantum state of one or more cores. Take part then in the reaction protons and neutrons (noted respectively p and N ), but also of other particles, the such electrons e-, the positrons e+

The nuclear reactions can be several types. To only quote most important:

• the fission: a heavy core breaks in several fragments. It is this type of reaction which is implemented in the atomic bombs of the type has, and, with a more peaceful aim, the nuclear plants.
• the fusion: several light cores amalgamate. It is the mode of production of energy of stars. Nuclear fusion is with the source of the Nucléosynthèse which makes it possible to explain the genesis of all the elements of the periodic Tableau of Mendeleïev and of their Isotopes. It is also the type of reaction which is used in the bombs called to hydrogen. The use of fusion at ends of civil energy production is not controlled yet. Its control is the object of the international project ITER.
• the Radioactivity: a core emits one or more particles spontaneously. One distinguishes the radioactivities $\ alpha$, where a helium core is emitted; the radioactivity $\ beta$ where either a electron and an electronic anti-neutrino are emitted ($\ beta^ \left\{-\right\}$), or a Positron and a electronic Neutrino ($\ beta^ \left\{+\right\}$) and the radioactivity $\ gamma$ by which a core loses its energy by an electromagnetic radiation of high energy.
• reactions of knocked-out or spallation: light particles (Neutron S for example) are sent on a core targets and expel one or more Nucléon S of this core.
• reactions of diffusion (elastic or inelastic): light particles or cores, which constitute the projectile, are sent on a target core but in order to avoid a head-on collision. The projectile is deviated by the target but modified the state of the latter. In the case of a elastic Scattering, the energy of the target is not modified, contrary to a inelastic Scattering.

## Applications of the nuclear physics

### Astrophysics

The Nucléosynthèse explains manufacture in the Universe of the various cores which currently constitute it. Two quite distinct processes are however necessary to explain the abundance of different the éléements chemical in the universe:

• In a first phase, at the time of the Big Bang, is formésà to leave the Hydrogène, the cores of 2 H (Deuterium), 3 He, 4 He and 7 Li. Aucn heavier element is not synthesized, because this phase is relatively short. However, to form elements heavier than lithium, it is necessary to have recourse to a reaction utilizing three helium cores, known as Réaction triples alpha. This type of reaction is extremely difficult to realize and can be done only over period much longer than the few minutes of the paramount nucleosynthesis.
• the continuation of the nucleosynthesis occurs thus in the middle of the star S. One then speaks about stellar Nucléosynthèse. This one scince besides in two processes: slow nucleosynthesis, taking place in the stars, which makes it possible to synthesize the elements lighter than the Fer, then explosive nucleosynthesis, only produced during the star explosions, called Supernova E. One speaks then about explosive nucleosynthesis.

### Medicine

The Nuclear medicine rests on the use of radioactive sources and the interaction of these sources with human tissues. This interaction is exploited at ends of diagnosis (Radiologie for example) or of treatment (Radiothérapie). As from years 1980 developed the techniques of imagery by nuclear Magnetic resonance (IRM) which call upon the magnetic properties of the cores.

### Energy production

The production of nuclear energy can have two origins: the Fission of cores heavy (family of actinides like uranium) or the Fusion of light cores (of type Deuterium, Tritium).

The energy production can be:

• brêve and intense: it is the principle of a nuclear bomb,
• controlled (at ends of civil but so military production).

#### Controlled energy production

Currently, the industrialists can exploit only the energy which comes from the fission of the heavy cores. Energy is then used:
• is to produce electricity, it is the case of the nuclear plants

• is to make it possible to drive a vehicle, particularly in the maritime field (aircraft carrier, submarines with nuclear propulsion) and of the aerospace one

.

The use of fusion at ends of civil energy production is not controlled yet. Its control is the object of the international project ITER.

## Research organizations in Nuclear physics

### In France

• Commissariat à l'Energie Atomique (ECA)
• Large National Accelerator of Heavy Ions (GANIL, Caen)
• Laboratory of the linear accelerator (LAL, Orsay)
• Center of nuclear spectrometry and mass spectrometry (CSNSM, Orsay)
• Imagery and modeling in neurobiology and cancerology (IMNC, Orsay)
• SUN synchrotron (Saclay)
• European Synchrotron Radiation Facility (ESRF, Grenoble)
• Institute Laue Langevin (ILL, Grenoble)
• Laboratory Leon Brillouin (LLB, Orsay)
• National laboratory Henri Bequerel (Saclay)
• Center of nuclear studies (CENBG, Bordeaux Gradignan)
• Institute of nuclear physics (IPN, Orsay, Villeurbanne)
• Corpuscular Physics laboratory (LPC Caen, Clermont-Ferrand)
• multi-field Institute Hubert Curien (IPHC, Strasbourg)
• nuclear Physics laboratory and of high energies (LPNHE, Paris Jussieu)

### In the world

• Oak Ridge National Labotory (ORNL)
• Los Alamos National Labotory (LANL)

## See too

### External bonds

• Service of Nuclear physics CEA/DAM, France

• National institute of Nuclear physics and Physics of the Particles (In2p3), France
• Large National Accelerator of Heavy Ions (GANIL), France
• Commissariat à l'Energie Atomique (ECA), France
• Gesellschaft für Schwerionenforschung (GSI), Germany
• Joint Institute for Nuclear Research (JINR), Russia
• National Laboratory, (ANL) the United States
• Center European of Nuclear Research, Swiss Argonne
• Riken, Japan

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