Dr. Sara Pozzi
University of Michigan
Dual Particle (Neutron and Gamma ray) Imaging
The Dual-Particle Imager (DPI) is an instrument based on scintillation detectors (liquid organic and sodium iodide) that has been proposed as a device capable detecting, localizing, and characterizing SNM. The DPI is sensitive to fast neutrons and gamma-rays, with the ability to separately reconstruct images and emitted energy spectra for both particle types. To aid this effort, new advanced imaging techniques are being developed for use with the DPI that improve image resolution and allow for the isolation of emitted energy spectra in a multi-source environment.
The system is fully scalable, and a handheld version of the DPI is also being developed. This smaller system relies on an array of stilbene scintillator bars, which are sensitive to both neutrons and photons. Each bar is read-out using silicon photomultipliers at either end, allowing for axial position sensitivity.
I will present results from the first experiments using dual particle imaging on category-I SNM. The experiments were performed at the Device Assembly Facility (DAF) at the Nevada National Security Site (NNSS) and included a 4.5-kg sphere and 4.1-kg disk of weapons grade plutonium as well as a 13.1-kg sphere of highly enriched uranium. The advanced imaging methods will demonstrate the ability of the DPI to locate and characterize these SNM sources when other sources, which also emit neutrons and gamma-rays, are present in the field of view.
Monte Carlo Methods for Radiation Detection
In the past few years, efforts to develop new measurement systems to support nuclear nonproliferation and homeland security have increased substantially. Monte Carlo radiation transport is one of the simulation methods of choice for the design of new measurement systems and for the analysis of data from existing systems; it allows for accurate description of geometries, detailed modeling of particle-nucleus interactions, and event-by-event detection analysis.
In this presentation, I will describe the use of the Monte Carlo code MCNPX-PoliMi for nuclear-nonproliferation applications, with particular emphasis on the simulation of spontaneous and neutron-induced nuclear fission. In fact, of all possible neutron-nucleus interactions, neutron-induced fission is the most defining characteristic of special nuclear material (such as U-235 and Pu-239), which is the material of interest in nuclear-nonproliferation applications. I will describe simulations of pulse height tallies of neutron interactions in existing and new organic scintillators, time-dependent cross-correlation measurements, and neutron and gamma ray multiplicity measurements. All of these simulation results are validated with experimental results.
Neutron Detection in Proton Therapy for Cancer Treatment
Recent advances in nuclear detection capabilities, including new detection materials and readout electronics, promise to have an impact in the development of new cancer therapy treatments. I will present new neutron and photon detection techniques that will be used in instruments and algorithms for application in cancer treatment facilities. The urgent needs in this area include, but are not limited to, neutron dosimetry for proton therapy facilities and the evaluation of the biological damage to cells by neutron irradiation. Proton therapy facilities use high-energy proton beams to destroy cancerous cells. In this approach, secondary radiation is produced due to proton interactions with the body and surrounding materials. This secondary field, which includes both neutrons and photons, must be accurately characterized in order to determine its effect on patients and medical personnel. An interdisciplinary approach, including both simulation and experiments, is required to tackle these complex and urgent challenges.
Science and Technology for Nuclear Treaty Verification
Since the discovery of fission, nuclear chain reactions, and nuclear weapons, preventing the spread of nuclear weapons has become a top priority for our nation and the world. Several international treaties have been put into place to curb the expansion of nuclear capabilities. Nevertheless, there are states that may be pursuing elements of an overt or covert nuclear weapons program. New science and technology developments are needed to verify the existing or proposed treaties in this area and to ensure that nuclear weapons are never used again.
In this presentation, I will discuss these challenges and the recent advances in science and technology that contribute to solving them. I will present our Consortium for Verification Technology, a consortium of 12 universities and 9 national laboratories working together on these issues. I will describe our studies on the fundamental emissions from nuclear fission, and the development of new detection systems for nuclear materials detection, localization, and characterization. Finally, I will touch upon the detection and characterization of nuclear explosions, with reference to the January 6, 2016 event in North Korea.
Professor Sara Pozzi earned her M.S. and Ph.D. in nuclear engineering at the Polytechnic of Milan, Italy in 1997 and 2001, respectively. She is a Professor in the Department of Nuclear and Radiological Sciences at the University of Michigan where she established and is the leader of the Detection for Nuclear Nonproliferation Group (DNNG). Her research interests include the development of new methods for nuclear materials detection, identification, and characterization for nuclear nonproliferation, safeguards, and national security programs.
Professor Pozzi is the founding Director of the Consortium for Verification Technology (CVT) 2014-2019 and the Consortium for Monitoring, Technology, and Verification (MTV) 2019-2024, two large consortia of multiple universities and national laboratories working together to develop new technologies needed for nuclear treaty verification. In this capacity, she directs the work of 25 faculty members and over 250 students engaged in research projects within the consortium. She is the co-author of the Monte Carlo code MCNPX-PoliMi, which is being used at over 50 institutions world-wide. Her publication record includes over 400 papers in journals and international conference proceedings. She presented over 100 invited lectures, both nationally and internationally. She has graduated 25 Ph. D. students who went on to develop successful careers at the national laboratories, academia, industry, and government. She served the NPSS in many positions, including member of Radiation Instrumentation Technical Committee (RITC), RITC Awards Chairperson, and Nuclear Science Symposium Co-chair for Atlanta, 2017, and Boston, 2020 (virtual).
She is the recipient of many awards, including the 2006 Oak Ridge National Laboratory Early Career Award, 2006 Department of Energy, Office of Science, Outstanding Mentor Award, 2012 INMM Edway R. Johnson Meritorious Service Award, 2017 IEEE Distinguished Lecturer, 2018 Rackham Distinguished Graduate Mentoring Award, and 2021 American Nuclear Society Gail De Planque Award. She is a Fellow of the American Nuclear Society, the Institute of Nuclear Materials Management, and the IEEE.