PNNL

Daniel Stephens is a distinguished nuclear scientist and senior executive with over 30 years of radiation detection and nuclear science research experience. Since joining Pacific Northwest National Laboratory (PNNL) in 2003, he has served in multiple roles—from individual contributor to institutional leader—making significant contributions to national security missions. Dr. Stephens serves as the director of the Nuclear Nonproliferation and Security Sector within the National Security Directorate. In this role, he is responsible for a business portfolio that represents nearly 25% of PNNL’s total annual budget ($1.64 billion in fiscal year 2025). His strategic relationship-building across federal agencies and senior administration and congressional stakeholders has resulted in substantial program growth, with over $100 million in new initiatives developed under his leadership. 

Dr. Stephens’ leadership philosophy centers on fostering scientific excellence while delivering transformative mission impact. He spent four years as technical group manager of the Radiation Detection and Nuclear Sciences group, overseeing more than 60 technical staff; world-class laboratory operations both on-site and at facilities in Japan (KEK), Canada (SNOLAB), and South Dakota (SURF); an active postdoctoral and student program; and research spanning basic nuclear and high-energy physics to sensitive nuclear security programs. 

He also served as the interim chief science and technology officer of the National Security Directorate, where he was responsible for the research and development investment strategy across the directorate, balancing immediate operational needs with long-term scientific vision. 

As a trusted advisor, Dr. Stephens translates technical capabilities, emerging needs, and institutional investments into solutions that address national priorities. He served as the chief scientist and manager supporting deployments of radiation portal monitors at the nation’s borders for U.S. Customs and Border Protection within the Department of Homeland Security. This role required managing 700-plus interdisciplinary staff across science, engineering, procurement, construction, and deployment functions—representing one of the largest and most complex projects in PNNL history. He also served as a technical advisor during an off-site assignment to the National Nuclear Security Administration Office of Nonproliferation Research and Development for the Advanced Materials and Special Nuclear Material Movement Detection programs. In this role, he provided direct support to senior federal program managers and influenced interagency strategy development.

Dr. Stephens is a recognized thought leader who engages internally and externally to shape nuclear nonproliferation and security missions and empower the next generation of technical staff. Dr. Stephens is an alumnus of the Oppenheimer Science and Energy Leadership Program, the premier leadership development program of the Department of Energy. He is also a fellow in Massachusetts Institute of Technology’s Seminar XXI, a year-long fellowship designed for current and future leaders in the U.S. government’s national security community. He has a distinguished history of scholarship, including several highly cited research papers, and was elected as a senior member of the IEEE Nuclear and Plasma Sciences Society in 2018. Dr. Stephens holds a PhD in nuclear engineering from the University of Tennessee.

• Nuclear nonproliferation
• National and homeland security applications of novel radiation detection instruments
• Advanced spectroscopic identification algorithms
• Alternate signatures for radioactive materials
• Sensor networking
• Operational testing and evaluation of sensor systems
• Space radiation environment modeling and experiment

• PhD in Nuclear Engineering, University of Tennessee
• MS in Nuclear Engineering, University of Tennessee
• MS in Physics, University of Tennessee
• BS in Physics, Georgia Southern University 

• Member, American Association for the Advancement of Science
• Elected Senior Member, Institute of Electrical and Electronics Engineers, Division of Nuclear and Plasma Science
• Appointment to the External Board of Advisors, Department of Nuclear Engineering, University of Tennessee, 2014–2019
• Member, Radiation Instrumentation Steering Committee, IEEE Nuclear and Plasma Science Society, 2014–2017