Download Thesis in Pdf Format - Theoretical Nuclear Physics and ...

Chapter 1
Introduction
Nuclear physics is the study of atomic nuclei. The primary aim of nuclear physics
is to understand the force between nucleons, the structure of nuclei, and how nuclei
interact with each other and with other subatomic particles. These three questions
are, to a large extent, related to each other. It has been known for years that the
nucleus is a many-body system of protons and neutrons, the two lightest members
of the baryon family, that is held together by the strong nuclear force. Traditional
models of nuclei rely on the shell model, where it is assumed that both protons and
neutrons are moving independently in an average mean-field potential, which expresses
the interaction of the nucleon with the surrounding medium. The nucleons
then occupy the lowest single-particle levels up to the Fermi energy, whereas the
single-particle levels above the Fermi energy remain unoccupied. From systematic
investigations for a large number of target nuclei a richness of precise information
about the independent-particle wave functions and spectroscopic strengths was assembled
[1], and it turned out that many nuclear features could be explained within
this single-particle picture.
However, as nucleons in the nucleus interact with each other through the strong,
short-ranged interaction, a number of nuclear structure properties remains unexplained
in the basic independent-particle model. An extensive amount of measurements
has made it clear that the occupancy of the single-particle level is substantially
smaller than what is expected in a naive independent-particle model. This observation
has resulted in the conjecture that 2/3’s of the nucleons in the nucleus act as
independent quasi-particles, whereas the remaining ones are then correlated [1].
A full understanding of the nucleus can not be achieved without some knowledge
about the underlying mechanisms that are responsible for the strong nuclear force.
The strong nuclear force manifests itself as a result of the strongly interacting quark
and gluon constituents which build up the nucleon. A better understanding of
the quantum chromodynamics (QCD) theory which describes the strong interaction
between quarks and gluons, will most certainly lead to a better understanding of
1