5.5.1. Nuclear structure

A number of teams around the world are engaged in the co-ordinated evaluation and compilation of nuclear structure data, under the auspices of the International Atomic Energy Agency. This International Network for Nuclear Structure Data Evaluation generates updated Evaluated Nuclear Structure Data Files (ENSDF), and is responsible for the evaluation of all the mass-chains on a regular basis (NNDC, 1987; Bhat, 1992). The resulting files are maintained by the National Nuclear Data Centre at Brookhaven National Laboratory, along with other services (Dunford, 1994; Kinsey et al, 1994). Available databases include ENSDF, atomic masses, NuDat (basic nuclear data extracted from ENSDF, including radionuclidic decay data), RADLST (calculated decay parameters from ENSDF), CSISRS (experimental cross­section data) and ENDF-6 (evaluated nuclear reaction and decay data in ENDF-6 format for applications in the nuclear industry). Details of the methods of data retrieval from NNDC are given in Appendix A, including access to the ENDF-6 files (Dunford, 1992). Theoretical decay data have been incorporated into this library for a number of important short-lived fission products, including delayed-neutron data and continuum spectra (Brady and England, 1989).

NUBASE is a database that contains the main nuclear and decay properties of nuclides in their ground and isomeric states (Audi et al, 1996 and 1997). These data have been primarily derived from ENSDF and the atomic mass evaluation of Audi and Wapstra (1995). Experimentally-measured nuclear parameters have been compiled for virtually all known nuclides, with some values estimated by systematic extrapolation. Recommended data are listed for mass excess, excitation energy of isomeric states, half-life, spin and parity, decay modes and branching fractions, as well as isotopic abundances for the stable nuclei and a list of relevant references.

The Table of Isotopes has a long and respected history, culminating in the release of the eighth edition in 1996 (Firestone et al, 1996). A CD-ROM is also included that contains all of the recommended decay-scheme data, and this vehicle will be preferentially used to communicate updates (Firestone et al, 1998). The main table is initially ordered by mass number and then by atomic number, with abbreviated mass — chain decay schemes that give the adopted half-lives, spin-parity and Q-values. Data are listed for each ground state and isomer with half-lives > 1 sec. ENSDF evaluations have been adopted whenever the authors judged this data source to be appropriate. Significant amounts of nuclear data are contained within this immense document/file, and the reader is referred to the original publication for greater detail. Other specialised decay-data compilations have been published (e. g., Reus and Westmeier, 1983; Westmeier and Merklin, 1985; Rytz, 1991; Nichols, 1996), but few appear to have been maintained in the same rigorous manner as ENSDF and the Table of Isotopes. Both are comprehensive and contain decay data for approximately 2500 radionuclides, effectively covering all nuclides that have been observed and characterised to some degree. The ability to inspect and use these data via a CD — ROM and the World Wide Web adds considerable strength to their commonality of use.