28 MAINTAINING THE QUALITY AND CREDIBILITY OF LARGE NUCLEAR DATABASES THROUGH EXTENDED MULTINATIONAL INITIATIVES A. L. Nichols 1 , S. Dunaeva 1 , A. Trkov 2 , V. Zerkin 1 1 Nuclear Data Section, Department of Nuclear Sciences and Applications, International Atomic Energy Agency, Vienna, Austria 2 Institut Jozef Stefan, 1000 Ljubljana, Slovenia Multinational efforts have ensured the development and maintenance of a number of important databases to cover the worldwide demand for access to nuclear reaction cross sections and nuclear structure and decay data. Compilations for EXFOR (EX change FOR mat (for nuclear reaction cross sections)) and evaluations for ENSDF (E valuated N uclear S tructure D ata F ile) were placed on international footings in 1970 and 1974, respectively. Both have been maintained ever since through the combined efforts of a number of individuals, research groups and national/international data centres brought together collectively under the auspices of the International Atomic Energy Agency (IAEA). ENDF (E valuated N uclear D ata F ile) databases are normally sponsored on a national basis, and their format (ENDF-6) and contents constitute the backbone of the necessary input data for a wide range of nuclear applications. The most recent studies and activities to improve the contents and user-friendliness of the three forms of database are described, and emerging problems and solutions are identified. 1. Introduction There are many distinct advantages associated with maintaining healthy sets of recommended nuclear data in a computerised form through the organised efforts of multinational networks: (a) maintenance of well-defined archives of nuclear data for future generations, (b) results in valuable interplays between nuclear reaction and decay data studies to define nuclear parameters to good accuracy, (c) significant impact of the recommended data on developing nuclear theories, (d) assists in the resolution of contradictory results, (e) identifies requirements for and stimulates new measurements, (f) benefits to users in many applied areas - nuclear medicine, analytical science, environmental monitoring, nuclear engineering, etc. Members of such networks can take great personal pride in assisting nuclear physicists and nuclear engineers with their everyday nuclear data needs. Many substantial nuclear data libraries can be found on the Web site of the International Atomic Energy Agency (IAEA). The most noteworthy are EXFOR (EX change FOR mat – extensive compilation of experimentally measured cross sections), ENDF (E valuated N uclear D ata F ile – nuclear applications libraries) and ENSDF (E valuated N uclear S tructure D ata F ile), which are continuously maintained multi-nationally (EXFOR and ENSDF), or periodically at a national level (ENDF). 2. EXFOR: EXtended FORmat for nuclear reaction cross-section data EXFOR is an experimental nuclear reaction data library (also known as CSISRS in the USA) compiled on a continuous basis by the International Network of Nuclear Reaction Data Centres under the coordination of the IAEA Nuclear Data Section (http://www-nds.iaea.org/nrdc/ ) [1]. This database is commonly used as the starting point for cross-section evaluations, as a primary data source when evaluations are unavailable, and by nuclear physics researchers measuring or calculating cross-section data (http://www-nds.iaea.org/exfor/ and on CD-ROM). Entries within EXFOR can also be used to generate bibliographic information for CINDA (http://www-nds.iaea.org/cinda/) [2]. The EXFOR and CINDA libraries contain neutron-induced, charged-particle-induced and photonuclear data and bibliographic information, including integral and all types of differential cross sections, resonance parameters, polarization data, fission product yields, and other related data for projectile energies up to 1 GeV. The EXFOR database was established in the 1960s, with the adoption of a working agreement between the four principal nuclear data centres to form the International Network of Nuclear Reaction Data Centres (NRDC): International Atomic Energy Agency, Nuclear Data Section (IAEA-NDS), Vienna, Austria; Nuclear Energy Agency Data Bank, OECD, Paris, France; National Nuclear Data Center (NNDC), Brookhaven National Laboratory, USA; and Russian Nuclear Data Centre, Institute of Physics and Power Engineering, Obninsk, Russian Federation. A further nine specialised nuclear data centres assist in the compilation of EXFOR entries, and are members of the NRDC: Russian Nuclear Structure and Reaction Data Centre, Moscow, Russian Federation; Centre for Photonuclear Experiments Data, Moscow, Russian Federation; Centre of Nuclear Physics Data, Russian Federal Nuclear Centre, RFNC-VNIIEF, Sarov, Russian Federation; China Nuclear Data Centre, Beijing, China; Nuclear Data Centre, Japan Atomic Energy Agency, Tokai-Mura, Japan; Japan Charged-Particle Nuclear Reaction Data Group, Hokkaido University, Sapporo, Japan; Nuclear Data Evaluation Laboratory, Korea Atomic Energy Research Institute, Yusong, Taejon, Republic of Korea; Charged-Particle Nuclear Reaction Data Group, Debrecen, Hungary; and Ukrainian Nuclear