Nuclear Structure and Radioactive Decay Resources at the US National Nuclear Data Center

Abstract

The National Nuclear Data Center has a long tradition of evaluating nuclear structure and decay data as well as offering tools to assist in nuclear science research and applications. With these tools, users can obtain recommended values for nuclear structure and radioactive decay observables as well as links to the relevant articles. Some of the activities are described in this article. 1 ENSDF The Evaluated Nuclear Structure Data File (ENSDF) stores recommended nuclear structure and decay data for all nuclei. ENSDF deals with properties such as: - nuclear level energies, spin and parity, half-life and decay modes, - nuclear radiation energy and intensity for different types, - nuclear decay modes and their probabilities. The data in ENSDF is incorporated after a careful compilation and analysis followed by a peer-reviewed refereeing process. Nearly 40 physicists worldwide contribute to ENSDF. In the last 4 years, an average of 230 nuclides was evaluated per year and nearly 80% of the evaluation work was performed by evaluators from the USA and Canada. The management of ENSDF resides at the NNDC, which is also responsible for the maintenance of the many codes used in the evaluations. The contents of ENSDF are stored in a relational database, which can be accessed electronically at http://www.nndc.bnl.gov/ensdf. This web site contains several search forms as well as an index to the database. ENSDF evaluations for A = 3-20 are published in Nuclear Physics A, the rest are published in the Nuclear Data Sheets journal, published by Elsevier, http://www.nndc.bnl.gov/nds. More details about ENSDF can be found in earlier publications (1). Any nuclide that has been reported as experimentally observed is included in ENSDF. As of today, it includes 3,011 nuclides with a total of 146, 314 nuclear levels. In order to illustrate the richness of the database and our current knowledge of nuclear structure, two plots are presented. In figure 1 we plot the distribution of largest spin values. At the extreme of the distribution is 152 Dy with a J + = 68 + excited level, with other rare earth nuclides also showing very high angular momentum values. One can also query the database to plot the number of levels distribution, which is shown in figure 2. In this case, the nuclei at the extreme are two doubly magic cases, 40 Ca and 208 Pb, both with more than 500 levels.