Fundamental Nuclear Science
Leveraging advanced experimental techniques and state-of-the-art facilities across North America, including the Facility for Rare Isotope Beams (FRIB), our group addresses the most exciting questions in fundamental nuclear science.
Nuclear astrophysics
A major goal of nuclear astrophysics is to understand the origin of the elements in our solar system and throughout the cosmos. Nuclear reactions occurring in a variety of extreme astrophysical environments are responsible for producing most of the elements. However, our current understanding is limited, in part, by the scarcity of nuclear-reaction data on radioactive isotopes.
To address this, NPAT researchers conduct nuclear-reaction experiments at radioactive-beam and stable-beam facilities using both direct measurements and indirect techniques, such as the surrogate nuclear reaction method and the beta-Oslo approach. Additionally, the NPAT group performs cosmochemistry measurements to analyze the isotopic signatures of multiple elements in pre-solar grains and conducts decay-spectroscopy experiments on exotic nuclei to gain insights into the dynamics of astrophysical environments.
Nuclear structure
NPAT researchers investigate the properties of exotic nuclei to better understand nuclear forces, the organization of nuclear matter, and the limits of nuclear stability. A key focus is studying the evolution of properties, such as nuclear shell structure and nuclear shapes, by extending experiments to isotopes with greater proton-to-neutron imbalances.
These experiments utilize sophisticated decay-spectroscopy techniques and advanced reaction methods, such as Coulomb excitation with high-energy beams. To probe these highly sensitive radioactive nuclei, we employ state-of-the-art radiation-detection systems—including the FRIB Decay Station Initiator and GRETINA, paired with the CHICO-X charged-particle detector.
Fundamental symmetries
Certain radioactive nuclei serve as sensitive testing grounds for detailed investigations of the weak nuclear force, one of the four fundamental forces of nature. By trapping radioactive lithium-8 and boron-8 ions in a vacuum and detecting the radiation emitted during beta decay, NPAT researchers are conducting some of the most sensitive searches for phenomena beyond the Standard Model, helping to refine our understanding of this poorly characterized force.
Nuclear data for applications
NPAT conducts cutting-edge experiments on nuclear cross-sections, neutron-induced reactions, and fission processes, leveraging modern facilities, advanced detection systems, and interdisciplinary collaboration.
Nuclear reactions
Nuclear cross-section measurements provide the data that underpin our nuclear-security missions in stockpile stewardship and nuclear forensics and the development of next-generation nuclear power plants. These applications require an improved understanding of neutron-induced reactions on radioisotopes.
The NPAT Group employs experimental approaches such as the surrogate nuclear reaction method and the beta-Oslo technique to obtain data on a wide range of radioisotopes, from nuclei just off stability to short-lived fission products. Additionally, direct measurements of actinides are being pursued to determine cross sections that are otherwise difficult to measure. These efforts are enabled by modern radioactive-beam facilities such as FRIB, advanced radiation detection systems, and close collaboration with radiochemists and nuclear theorists at LLNL.
Fission
A comprehensive understanding of nuclear fission is essential for the nation’s nuclear-security missions. Fission is a complex process in which heavy nuclei split into fragments, releasing neutrons, gamma rays, and significant amounts of energy.
The NPAT Group conducts experiments to measure key fission properties, including the cross section of neutron-induced fission, the yields of the resulting fission products, and the multiplicity of emitted neutrons and gamma rays. Notably, NPAT research has provided insights into how fission-product yields depend on the energy of the neutron or gamma ray that induces the fission reaction.
Fission products
One of the most reliable methods for determining fission-product yields is detecting the characteristic gamma rays emitted during the beta decay of fission products. NPAT researchers have developed a novel method to precisely measure the absolute intensities of these gamma rays. By producing pure samples with radioactive beams or chemically purifying irradiated samples, the NPAT Group achieves high-precision measurements for detecting beta-gamma coincidences.
Accelerator science
Our group operates a suite of particle accelerators at LLNL, capable of producing high-energy beams of electrons, neutrons, light ions, and photons. This suite includes:
- The 7-MeV deuteron accelerator for generating high-intensity neutron beams that enable nuclear cross-section measurements, material assay through gamma-ray spectroscopy, and experiments to study the effects of radiation on materials and component performance.
- The Photonuclear Reactions for Isotopic Signature Measurements (PRISM) accelerator for investigating the photonuclear properties of materials. This system accelerates electrons to energies of up to 55 MeV, directing them into a tungsten plate to produce high-energy x rays, which are then used to bombard targets. PRISM supports research in radiation effects, radiochemistry, medical isotope production, and photonuclear cross-section measurements.
- The mono-energetic gamma-ray (MEGa-ray) test station for producing electron bunches that collide head-on with a laser beam, boosting the photon energy from visible light to mono-energetic x rays through Compton scattering.
These advanced capabilities allow scientists to conduct fundamental nuclear science measurements, develop cutting-edge experimental techniques, and address a range of emerging programmatic needs.
