Daniel F. Hollenbach is a research and development staff member in the Radiation Transport and Criticality Group in the Nuclear Science and Technology Division. He received a B.S. degree in nuclear engineering from North Carolina State University in 1982, M.S. degree in nuclear engineering from the University of Washington in 1983, and Ph.D. degree in nuclear engineering from the University of Tennessee in 1992. His Ph.D. dissertation research focused on vectorization of the KENO V.a criticality safety code. His M.S. thesis research involved five parameter characterization of two-phase flow using the University of Washington nuclear reactor. From 1975 to 1979 he served in the U.S. Army as a Russian linguist. Between 1983 and 1988, he also spent 1-½ years with the Nuclear Regulatory Commission as a reactor inspector and 3-½ years as a nuclear engineer at the Puget Sound Naval Shipyard. While there Dr. Hollenbach was involved in a variety of research and analysis activities, including writing procedures for naval nuclear submarine refueling and collaborating on the development of a program to modify spent fuel shipping containers for the transport and storage of naval nuclear fuel. He is the primary author of the KENO-VI criticality safety code and the CSAS6 control model, which uses it. Research interests include the development and implementation of calculational methods using Monte Carlo transport theory emphasizing the area of criticality safety. Current research activities include the development and enhancement of neutral particle transport computer codes (e.g., KENO-VI, CENTRM, CSAS, etc.) at ORNL. He also occasionally performs code and cross-section validation studies and criticality safety analyses of systems containing fissile material. Side interests include naturally occurring fissile material systems and their effects (the OKLO reactor and deep-Earth reactors) and the production and distribution of fissile material in cosmic systems (production in stellar events and distribution in comets and asteroids). His sporting interests include running marathons (he is an active member of the Knoxville Track Club), sailing, skiing, and karate. Dr. Hollenbach is an active member of the American Nuclear Society and is involved with community activities such as science bowls and competitions.