The Shell-Model - Introduction


Introduction - The Shell-Model

The atomic nucleus presents one of the most challenging many-body problems. Recent experiments have been probing nuclei under extreme conditions of high spin, large deformations, high excitation energies (finite temperature), and neutron-to-proton ratios at their limit of stability. A wealth of experimental data on such nuclei is expected in the near future from new radioactive beam facilities. The understanding of nuclear structure is important in various astrophysical applications and in tests of fundamental symmetries.

A major program in computational physics is to calculate nuclear properties from underlying realistic nuclear forces. The shell model is among the most fundamental models of nuclear structure; some of the effective interactions used in this approach can be traced back to the nucleon-nucleon G-matrix. In this model, valence nucleons (outside closed shells) move in a mean-field potential and interact via a residual nuclear force. The model (in its simplest non-interacting version) was introduced almost 50 years ago by Mayer [mayer,49] and by Haxel, Jensen and Suess [Haxel,49]. It has proven very successful in describing the properties of nuclei with few valence nucleons [Talmi,93], including energy levels, magnetic and quadrupole moments, electromagnetic transition probabilities, beta-decay rates and reaction cross-sections. It has also been used as the theoretical basis for several algebraic nuclear models. The shell model became the standard model for describing the systematics observed in the spectra and transition intensities of p- [Cohen,65], sd- [Wildenthal,88]-[Brown,88] and lower fp-shell [French,69]-[Martinez-Pinedo,97] nuclei. Since the size of the model space increases rapidly with the number of valence nucleons and/or orbits, full major shell calculations were limited to nuclei with A < 49 [Caurier,94]-[Martinez-Pinedo,97]. The Drexel University Parallel Shell Model (DUPSM) method is an approach recently developed to enable calculations of nuclear properties in large model spaces. We are developing this model and applying it at the forefront of nuclear structure physics.


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