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Nuclear physics
Radioactive decay
Nuclear fission
Nuclear fusion
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Nuclear physics is the field of physics that studies the building blocks and interactions of atomic nuclei.

It must not be confused with atomic physics, that studies the combined system of the nucleus and its arrangement of electrons, even if both terms are sometimes used synonymously in standard English.

Particle physics is a field that has evolved out of Nuclear physics and for this reason has been included under the same term in earlier times.

Nuclear power and nuclear bombs are the most commonly known applications of nuclear physics, but the research field is also the basis for a far wider range of less common applications, like e.g. in the medical sector (nuclear medicine, magnetic resonance imaging), in materials engineering (ion implantation) or archaeology (radiocarbon dating).

Contents

Forces

Nuclei are bound together by the strong force. The strong force usually acts over a very short range (a fermi or two, roughly one or two nucleon diameters) and causes an attraction between nucleons (protons and neutrons). However there are also halo-nuclei such as Lithium11 or Boron14 in which di-neutrons, or other collections of nucleons, orbit at distances of tens of fermis. This behaviour is beyond the descriptive capacity of usual wave mechanics. 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 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 is usually of a few Million electron Volts in magnitude, arising from to the exchange of mesons. The study of nuclei has been attempted by wave mechanicists, and it partially works in special cases (typically for simple spherical nuclei), but the general N-body problem in nuclear physics is best dealt with by meson theory (QCD) which always works [see ILLERT, 2008]. Another force, acting between mesons, is an order of magnitude weaker (about -0.3 Million electron Volts). Some argume that this arises from ghost particles blinking into and out of existence ("fizzing of the aether"), a kind of QED effect, whilst other suggest it is a Weak Force manifestation. Inter meson forces exist, regardless of what causes them, and theoretical debate continues.

REFERENCE

C. ILLERT [2008], "nuclear structure from naive meson theory", Proceedings of the 10th annual PIRT conference, Imperial College, London. The paper is at present accessible in electronic form on the internet site

www.physicsfoundations.org

or more specifically perhaps

http://www.physicsfoundations.org/PIRT_XI/texts.htm


 This section may require cleanup to meet Wikipedia's quality standards.
Please improve this section if you can. (March 2008)

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 Schrödinger 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 very important experimental fact implies that spherical nuclei have radii directly proportional to the cube root of their respective volumes (volume of a sphere = 4 / 3πR3). It says that nuclear volumes are generally equal to the sum of the respective volumes of constituent nucleons, like oranges packed together in a string bag. This single experimental fact shows that protons and neutrons are solid spheres with fixed volumes that are packed together in a nucleus, thereby refuting the various unphysical wave models that imagine nucleons to be either size-less point particles in potential wells, or else probability waves as in the "optical model".


Nuclei are not all spherical. Some can exist with giant haloes. Whilst others can also exist in giant cigar or ring states, superdeformed by excessive spin. All these are beyond the capacity of spherically symmetric potential well theory. Only naive meson theory works in general for all atomic nuclei [see ILLERT 2008].

REFERENCE

C. ILLERT (2008), "Nuclear Structure from Naive Meson Theory, Part 1", Proceedings of the 10th biannual PIRT conference, Imperial College London. The paper is at present accessible in electronic form on the internet site

www.physicsfoundations.org

or more specifically perhaps

http://www.physicsfoundations.org/PIRT_XI/texts.htm

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.

Nuclear activity

Alpha decay

Main article: Alpha decay

Beta decay

Main article: Beta decay

Gamma decay

Main article: Gamma decay

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

Fission

Main article: Nuclear fission

Fusion

Main article: Nuclear fusion

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 Curie 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.

See also

Physics portal

References

 This article does not cite any references or sources.
Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed. (March 2008)

Nuclear Physics by Irving Kaplan 2Nd edition, 1962 Addison-Wesley General Chemistry by Linus Pauling 1970 Dover Pub. ISBM 0-486-65622-5

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