In the past twenty years, the experimental study of nuclear physics has entered a new stage. Until fairly recently, the great majority of such investigations used probes from low-energy accelerators to study properties of nuclei.
Many unanswered questions remain in nuclear physics.
The shell model provides a good framework for understanding many different types of experiments, but we have no deep understanding of a vital ingredient, the nucleon-nucleon force. In fact, the structure of protons and neutrons themselves is a major question in the field of nuclear physics today. One question of fundamental importance is why quarks and gluons, two primary constituents of matter, remain confined within nuclear particles. Collisions between two heavy nuclei at high energies are predicted to form a region where the density of partons is so high that the confining interaction is reduced and the partons are free to travel across the full volume of the system. Nuclear Theory Nuclear theory seeks to understand the structure and interactions of the nucleons, atomic nuclei, and hadronic matter that compose the universe.