Our research has been supported by the National Science Foundation, Department of Homeland Security, Department of Energy, Defense Advanced Research Projects Agency, Defense Threat Reduction Agency, Nuclear Regulatory Commission, and industry.

Research Thrust 1: Ionizing Radiation Detection and Measurement

Nuclear nonproliferation and security are some of the major challenges associated with the expansion of nuclear power. Addressing these challenges requires both a sound nuclear policy and major advances in detection science and technology. We are pursuing research projects in collaboration with other academic departments, universities, and national laboratories, focusing on developing advanced technologies to safeguard nuclear technology and detect nuclear proliferation. Some of our recent projects include:

1) Remote discovery and monitoring of nuclear reactors using antineutrinos (Sponsor: DOE/NNSA)

We are part of the WATCHMAN scientific collaboration consisting of universities and national laboratories in the US and UK, with the goal of demonstrating remote monitoring of individual reactor operations at a significant distance using scalable water-based technology. WATCHMAN plans to deploy a 6-kton water-based antineutrino detector, NEO, at the Advanced Instrumentation Testbed (AIT) site. The AIT site consists of an underground laboratory in the Boulby mine in Northern England, located 26 km from the Hartlepool Reactor Complex. The project is supported by the NNSA’s Office of Defense Nuclear Nonproliferation, the DOE Office of Science, The Ministry of Defence, and The Science and Technologies Facilities Council.

2) Near-field reactor monitoring using antineutrinos (Sponsor: DOE/NNSA)

We are building and testing the first antineutrino directional detector that employs ⁶Li-doped pulse-shape-sensitive plastic called SANDD. Using solid-state materials enables fine-grained segmentation, leading to excellent spatial resolution. Combined with particle ID sensitivity, this is not only critical to reconstructing the direction of the antineutrino flux but could also enable aboveground antineutrino detection, which would be immensely beneficial to both the physics and nonproliferation communities. Additionally, we are investigating pulse shape discrimination using an alternative DAQ based on mass-produced ASICs with low cost per channel, excellent timing characteristics, and scalability to thousands of channels. The work is conducted in collaboration with Lawrence Livermore National Laboratory (LLNL) and the University of Hawaii, with support from LLNL.

3) Active interrogation (Sponsor: DHS and DOE/NNSA)

Active interrogation techniques can provide highly accurate information about special nuclear material (SNM) in many safeguards and verification settings. With the support of the Department of Homeland Security, the National Nuclear Security Administration, and the Consortium for Monitoring, Technology, and Verification, we have collaborated with partners at Los Alamos National Laboratory to conduct several experimental campaigns at the Device Assembly Facility at the Nevada National Security Site, MIT Bates Accelerator Laboratory, University of Notre Dame, and Institute for Nuclear Energy Research in Taiwan. We have been investigating novel methods to detect and characterize SNM, such as HEU, using active interrogation neutron sources to induce delayed neutron signatures that provide calibration-free isotopic identification.

4) Magnetic microcalorimeters (Sponsor: DOE/NNSA)

5) Coherent elastic neutrino-nucleus scattering – CEνNS (Sponsor: DOE/NNSA)

CEνNS is a recently measured neutrino interaction with a relatively high cross-section. CEνNS would allow small detectors (~10s of kg) to monitor nuclear reactors for malicious activity, such as fissile-material diversion, via their antineutrino signatures. We are collaborating with Lawrence Livermore National Laboratory to develop dual-phase (liquid and gas) argon CEνNS detectors. We aim to perform CEνNS measurements of reactor antineutrinos, to measure neutrinos below the IBD kinematic threshold (1.8 MeV), and to develop this technology and analysis methods for nonproliferation. In conjunction, we are investigating the potential vulnerability of neutrino detectors to “spoofing” signals that malicious actors might produce, and the steps nuclear regulators might take to ensure the validity of the neutrino signal. Additionally, CEνNS is a crucial tool in answering high-level fundamental physics questions and contributes to studies of sterile neutrinos, neutrino magnetic moment(s), solar nuclear fusion, and dark matter cosmology.

Research Thrust 2: High-Power Laser Science, Technology, and Applications.

Over the past two decades, remarkable developments in laser technology have led to peak powers exceeding 1 Petawatt and focal-spot intensities exceeding 10²² W/cm², establishing a new and promising field of relativistic optics and high-field science. Importantly, university settings now have access to laser systems capable of producing relativistic intensities. Applications of such systems in nuclear engineering are numerous and include producing intense pulses of X-rays, gamma rays, and neutrons, as well as extremely high-current electron and ion beams. Such systems have been used for isotope production, inertial confinement fusion via fast ignition, studies of ultrafast dynamics in solids, and even to demonstrate photon-photon scattering. Our current research activities include:

1) Laser spectroscopy for nonproliferation (Sponsor: DOE/NNSA)

Laser-based spectroscopy has several benefits for nuclear nonproliferation applications. One of which is the ability to excite isotopic, atomic, and molecular signatures. Another is that, due to optical nonlinear effects, one can overcome the diffraction limit and deliver energy to a remote (~km distance) target at high peak powers. We use high-intensity, ultrafast lasers at the Gérard Mourou Center for Ultrafast Optical Science to investigate optical remote sensing via filamentation. We primarily focus on laser-induced breakdown spectroscopy (LIBS) and laser-induced fluorescence (LIF) of various materials relevant to nonproliferation. Our most recent projects have focused on identifying signatures of uranyl fluoride, using LIF to detect stress in biota, and using LIBS to detect uranium-containing compounds. Other focuses include understanding filament plasma properties and controlling and optimizing laser beam parameters to improve the production and collection of optical signals at a remote distance. 

2) Remote optical detection of nuclear materials (Sponsor: DTRA)

Optical methods that detect photons in the UV, visible, and IR spectral regions originating from electronic transitions provide a modality for detecting nuclear materials that can complement traditional techniques based on ionizing radiation detection. Because electronic states are easier to excite than nuclear states and are typically more populated, they produce stronger, more easily detectable signals with improved statistical significance. Optical photons can also propagate readily through air over extended distances. We study the filamentation of ultrafast laser pulses in air to deliver the high electric fields needed to excite and/or ionize remote targets at distances of tens to hundreds of meters. Our research into the fundamental science behind the filamentation phenomenon spans three interrelated areas: we investigate the nonlinear propagation of intense, high-peak-power, ultrafast laser pulses; the excitation and ionization of the propagation medium to form the filament channel; and, ultimately, the interaction of the filament with the target.

3) Optical instrumentation for advanced reactors (Sponsor: DOE, INL)

With support from the U.S. Department of Energy and in collaboration with Ohio State University, Idaho National Laboratory, and private industry, we are investigating the linear and nonlinear optical properties of materials after irradiation and thermal annealing to support the development of optical instrumentation for use in advanced reactors. We investigate these properties using spectroscopy and nonlinear optical techniques enabled by high-energy, nanosecond-pulsed lasers. We further develop optical technologies for online fuel integrity testing in next-generation gas-cooled fast reactors.

4) Long-wave ultrafast coherent radiation sources (Sponsor: DOD/ONR)

Many laser-matter interaction processes, such as laser pulse filamentation, strong-field physics, and attosecond science, show strong wavelength dependence and favor longer wavelengths in the infrared spectral range, which has not been fully explored experimentally because suitable laser sources are lacking. With the support of the Office of Naval Research (ONR), we are investigating the use of Optical Parametric Chirped Pulse Amplification (OPCPA) to produce ultrashort, TW-class long-wave infrared pulses. We developed a seed source centered at 10 µm based on difference-frequency generation in an AGS crystal, and a 2.75-µm pump source based on a KTA parametric master oscillator power amplifier system to support OPCPA development in GaSe crystals.

5) Nuclear photonics (Sponsor: NSF)

The National Science Foundation’s facility, ZEUS (Zettawatt-Equivalent Ultrashort pulse laser System), is under construction at the Gérard Mourou Center for Ultrafast Optical Science and will house the nation’s most powerful laser. When interacting with matter, the 3-Petawatt ZEUS pulses will produce X-rays, gamma rays, neutrons, electrons, positrons, and exotic particles with energies that rival large scientific particle accelerator facilities. We are exploring the production and use of this high-energy radiation and particle beams for nuclear physics studies and applications.

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Past Projects

Low-dose shielded nuclear materials detection (Sponsor: NSF/DHS)

With support from the National Science Foundation’s Academic Research Initiative program and the Department of Homeland Security, we explored methods to detect shielded nuclear materials via active interrogation. In this multi-particle method, we used monoenergetic photons and/or neutrons to perform transmission imaging or induce photofission. We developed new solid-state glass-plastic composite neutron detectors to detect fast neutrons.

Radiation sensors and radiation-hard electronics based on graphene and other 2D materials (Sponsor: NSF/DHS and DTRA)

With support from the National Science Foundation’s Academic Research Initiative program and the Department of Homeland Security, we investigated non-traditional detection methods and detector architectures based on graphene, a material with numerous favorable properties for radiation detection. With support from the Defense Threat Reduction Agency, we studied radiation effects on other novel 2-dimensional materials for applications such as radiation-hard electronics.

Directional neutron detection (Sponsor: DOE/NNSA)

In collaboration with and with the support of Lawrence Livermore National Laboratory and the Department of Energy, we investigated the use of time projection chambers, sophisticated detectors used in particle and nuclear physics research, as high-performance directional neutron detectors for nonproliferation applications and for accurate measurement of fission cross-sections.

Fission distribution anisotropy studies by use of the surrogate reaction method (Sponsor: LLNL)

The surrogate reaction method is well suited for measuring short-lived nuclides. We are studying the low-energy fission anisotropy of Pu-239, U-235, and U-238, which is prevalent in surrogate reactions. In conjunction with microscopic cross-section models, this work can extend the surrogate method’s validity to measure cross-sections of short-lived isotopes at energies <1 MeV for nearly any actinide. This work was conducted in collaboration with Lawrence Livermore National Laboratory and Texas A&M University.

Compact dielectric structures pumped by ultrafast lasers could enable compact, high-efficiency accelerators and radiation sources for medical, scientific, and security applications. Within the UCLA-led GALAXIE consortium, we developed mid-infrared radiation sources based on nonlinear optical mixing processes. The project aimed to develop an ultra-bright, compact X-ray source for phase-contrast medical imaging.

Laser-based radiation sources based on microstructures (Sponsor: DTRA)

We pursued novel, high-risk approaches to particle acceleration to enable low-power ultrafast laser systems to achieve large acceleration gradients and replace traditional particle accelerators. These methods could enable the production of X-rays, gamma rays, and neutrons for active nuclear interrogation and medical applications.

Femtosecond laser spectroscopy for nuclear forensics (Sponsor: DHS)

Nuclear forensics is an area of increasing importance in the present climate of post-Cold War nuclear threats. In collaboration with ANL, LBNL, and LLNL, we investigated the potential of laser spectroscopy using shaped femtosecond pulses to enhance the sensitivity and speed of nuclear forensics techniques. 

Quantum remote sensing (Sponsor: DOE/NNSA, DARPA)

Advanced technology is needed to support aerial surveillance for detecting proliferation activities. We explored a novel class of sensors based on nonclassical manipulation of light to demonstrate imaging resolution that exceeds that of classical imaging systems.

Advanced pulse shaping techniques (Sponsor: DARPA)

With support from the Defense Advanced Research Projects Agency, we investigated phase-sensitive parametric interactions to produce complex shapes of ultrashort laser pulses needed for applications in ultrafast and materials science, nuclear fusion, and particle accelerators.