Nuclear physics

Overview
Nuclear physics is the branch of physics concerned with the nucleus of the atom. It has three main aspects: probing the fundamental particles (protons and neutrons) and their interactions, classifying and interpreting the properties of nuclei, and providing technological advances.

Forces
Nuclei are bound together by the strong force. The strong force acts over a very short range and causes an attraction between nucleons (protons and neutrons). The strong nuclear force is so named because it is significantly larger in magnitude than the other fundamental forces (electroweak, electromagnetic and gravitational). The strong force is highly attractive at only very small distances which, combined with repulsion between protons due to the electromagnetic force, allows the nucleus to be stable. The strong force felt between nucleons arises due to the exchange of gluons. The study of the strong force is dealt with by quantum chromodynamics (QCD).

Nuclear models
Nucleons in the nucleus move about in a potential energy well which they themselves create arising from their interaction, and movement, with respect to each other. Nucleons can interact with each other via 2-body, 3-body or multiple-body forces. The fact that many nucleons interact with each other in a complicated way makes the nuclear many-body problem difficult to solve.

There broadly exist two types of nuclear models which attempt to predict and understand characteristics of nuclei. These are microscopic and macroscopic nuclear models. Microscopic nuclear models approximate the potential which the nucleons create in the nucleus. Individual interactions are combined as linear sums of potentials. Almost all models use a central potential plus a spin orbit potential. The difference between models is then defined by the 3-body potential used, and/or the shape of the central potential. The form of this potential is then inserted into the Schrodinger equation. Solution of the Schrödinger equation then yields the nuclear wavefunction, spin, parity and excitation energy of individual levels. The form of the potential used to determine these nuclear properties indicates the type of microscopic model. The shell model and deformed shell model (Nilsson model) are two examples of microscopic nuclear models.

Macroscopic nuclear models attempt to describe such attributes as the nuclear size, shape and surface diffuseness. Rather than calculating individual levels, macroscopic models predict nuclear radii, degree of deformation and diffuseness parameter. A simple approximation for the nuclear radius is that it is proportional to the cube root of the nuclear mass.

$$R \propto A^{1/3}$$

This implies that all nuclei are spherical and their radius is directly proportional to the cube root of their volume (volume of a sphere = $$4/3 \pi R^3$$). Nuclei can also exist in a deformed shape and thus a degree of deformation ,$$ \beta_{2}$$, can be included to take this into account. The fact that the nucleus may not be entirely incompressible is also considered by the diffuseness parameter $$\delta$$. An example of a macroscopic model is the droplet model of Myers and Schmidt.

Some quite successful attempts have been made to combine the microscopic and macroscopic models together. These so called mic-mac models begin with a nuclear potential, solve the Schrödinger equation and proceed to predict macroscopic nuclear parameters. It is also possible to build real phyaical models of nuclei using small cylindrical Neodymium magnets that imply a protocol of accumulation (increase) that is related to the periods of the periodic table. See Talk:nuclear model. WFPMWFPM (talk) 05:02, 23 May 2008 (UTC)WFPMWFPM (talk) 14:12, 28 May 2008 (UTC)WFPMWFPM (talk) 14:34, 28 May 2008 (UTC)WFPMWFPM (talk) 14:47, 28 May 2008 (UTC)WFPMWFPM (talk) 15:28, 28 May 2008 (UTC)WFPMWFPM (talk) 15:31, 28 May 2008 (UTC)

Protons and neutrons
Protons and neutrons are fermions, with different values of the isospin quantum number, so two protons and two neutrons can share the same space wave function. In the rare case of a hypernucleus, a third baryon called a hyperon, with a different value of the strangeness quantum number can also share the wave function.

Gamma decay
Here, a nucleus decays from an excited state into a lower state by emitting a gamma ray.

History
The history of nuclear physics began with the discovery of the nucleus by Rutherford in 1911. While the work on radioactivity by Becquerel, Pierre and Marie Cure predates this, an explanation of radioactivity would have to wait for the discovery that the nucleus itself was composed of smaller constituents, the nucleons. Attempts to split the atom led to the discovery of nuclear fission.