This personal retrospective covers half a century of the development of our understanding of the atomic nucleus with particular reference to the writer’s involvement in it: nuclear instrumentation, nuclear photodisintegration, the early years of the shell model, nuclear symmetries, isospin, and β-decay. “. . . a breaker of stones on an old road to a not yet clearly marked destination.”
This article reviews experimental data on the orbitally excited charmed mesons, commonly called D**s, including measurements of their masses and widths as well as information on their production and decay properties. We use all available experimental data to calculate average values for the masses and widths of the six known D**(+)s. Measurements of blanching ratios, decay angular distributions, and production momentum spectra are tabulated, We also summarize the evidence supporting their spin-parity assignments. The measurements are compared with theoretical predictions from a quark model and from calculations using heavy-quark symmetry. Prospects for future measurements of these D**s and of other excited states yet to be discovered are discussed.
One of the new directions in nuclear science is the exploitation of beams of exotic nuclei. This field has grown tremendously in the past few years owing to considerable progress in the production and isotopic separation of secondary beams. This article summarizes the methods of radioactive ion production, the techniques used in isotope separation, and the scientific frontiers of this field. The production methods of secondary beams range from Coulomb barrier reactions to reactions at relativistic energies. New advances in high-intensity and high-energy accelerator facilities and new efficient separators based on the on-line separation and the in-flight methods have increased secondary beam intensity and selectivity. The combination of cooler and storage devices with a separator has opened a new field for experiments and applications.
After giving a brief historical overview, we use simple few-body models to illustrate the basic properties of halo states. Giant halos may exist in certain excited levels, although this is still very hypothetical. The main part of the paper is dedicated to the momentum spectra of fragments from breakup and to the beta decay of halo states.
Positron emission tomography (PET) is a new technique increasingly used in clinical medicine and research to create images that show physicians and scientists how effectively certain tissues are performing their physiological functions. It does this by determining the spatial distribution of radioactive nuclei that emit a positron. These nuclei are introduced to the body as ''labels'' on tracer molecules designed to probe physiological processes such as tissue perfusion or sugar metabolism. The PET scanner, based on detection techniques from nuclear and particle physics, produces three-dimensional (3-D) images using the methods of computed tomography (CT). PET isotopes are produced on-site by small cyclotrons or linear accelerators and are synthesized into highly specific chemical agents by automated systems. Physiological modeling is used to relate the PET measurements to metabolic parameters. PET plays an increasingly important role in the diagnosis of cancer, heart disease, and illnesses of the brain such as epilepsy, stroke, and the dementias. It is used as a basic research tool in studying the functional anatomy of the brain.
