Jeffrey O. Johnson is a senior research and development staff member of the Radiation Transport and Criticality (RTC) Group within the Nuclear Science and Technology Division (NSTD) at Oak Ridge National Laboratory (ORNL). He received a B.S. degree in Nuclear Engineering in 1978, a M.S. in Nuclear Engineering in 1980, and a Ph.D. in Nuclear Engineering in 1987, all from the University of Tennessee. He worked on his M.S. and Ph.D. research as a Graduate Research Assistant at ORNL from 1978 to 1986. His Ph.D. dissertation involved developing and validating a continuous-energy Monte Carlo code system (MICAP) for analysis of ionization chamber responses to mixed neutron and photon radiation fields. He became a full-time research staff member in the Engineering Physics Division at ORNL in 1986 and has also previously served as a group leader for the Applied Physics Group in the Computational Physics and Engineering Division of ORNL from 1996-2001 and for the Shield Design Group in NSTD from 2003-2006. During his career, he has participated in the shield design and analysis for space-based assets of the Strategic Defense Initiative Program and has managed and been the technical point of contact for the Defense Threat Reduction Agency Radiation Environments Program and Radiological Environments Program II, the U. S. Army National Ground Intelligence Center Nuclear Hardening Program, and Army Research Laboratory Nuclear and Directed Energy Weapon Effects Program at ORNL. From 1997 to 2001, he led the Spallation Neutron Source (SNS) Project Neutron Source Systems Development R&D Program and the Accelerator and Target Systems Neutronic and Shielding Design Program. The SNS project work entailed coupled Monte Carlo/Discrete Ordinates radiation shielding analysis methods development and application, target station design, accelerator facility shield design, and radiation transport graphical interface and analysis design tool development. From 2003 to 2005, he was the WBS manager and technical lead for the Space Reactor Shield Design Program of NASA’s JIMO/Prometheus Project with responsibilities including overall management of all design, procurement, fabrication, installation, and testing of the reactor shield segment. His areas of expertise include: (1) radiation transport analysis associated with shield design and effectiveness for terrestrial, space based, and accelerator driven systems; (2) methodology development; and (3) radiation detector design and analyses. He currently serves as a subject matter expert for armored vehicle radiation shielding design and analyses for the Army Research Laboratory, U. S. Army National Ground Intelligence Center, and U. S. Marines. He is a member and subject matter expert in radiation shielding materials, radiation transport methods development, and nuclear interaction data for the NASA Radiation Discipline Working Group and a member and subject matter expert in nuclear and radiological event modeling and simulation for the NNSA Advisory Panel on Consequence Management. He has been an active member of both the local section and national American Nuclear Society (ANS) since 1976. He is currently a member of the ANS Radiation Protection & Shielding Division (RPSD), Reactor Physics Division (RPD), and Accelerator Applications Division (AAD), serving in several executive positions for the RPSD over the years. He has authored or co-authored over 100 ORNL Technical Memorandums and papers in proceedings of national and international scientific meetings and has presented or contributed to over 100 presentations at national and international scientific meetings.