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DOE OSTI2024

Nuclear-matter saturation and symmetry energy within Δ -full chiral effective field theory

Nuclear saturation and the symmetry energy are key properties of low-energy nuclear physics that depend on fine details of the nuclear interaction. The equation of state around saturation is also an important anchor for extrapolations to higher densities and studies of neutron stars. Here we develop a unified statistical framework that uses realistic nuclear forces to link the theoretical modeling of finite nuclei and infinite nuclear matter. We construct fast and accurate emulators for nuclear-matter observables and employ an iterative history-matching approach to explore and reduce the enormous parameter domain of Δ -full chiral interactions. We perform rigorous uncertainty quantification and find that model calibration including O 16 observables gives saturation predictions that are more precise than those that only use few-body data. Published by the American Physical Society 2024

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2021

The Role of Nuclear-Conventional Intermingling on State Decision-making and the Risk of Inadvertent Escalation

The questions answered by this report are: What are the implications of nuclear and conventional intermingling on crisis stability and the potential risk of miscalculation?, and Specifically, how might entanglement influence US and competitor decision making during crisis and conflict? In practice, there are three main forms of nuclear-conventional intermingling. First, intermingling between nuclear and non-nuclear weapon systems can occur via the fielding of dual capable delivery systems like missiles or aircraft. Second, intermingling can happen due to the co-location of nuclear and non-nuclear forces and their support structures—for example, the co-location of strategic bombers and general-purpose aircraft, or the co-location of strategic submarines and general-purpose vessels. Third, intermingling can occur via convolving nuclear and conventional military command and control systems, to include ballistic missile early warning and potentially space surveillance systems as well. All three forms of nuclear-conventional intermingling have significantly increased since the end of the Cold War, driven by both technological and doctrinal changes. However, there are important differences in the rationale behind, and also the risks associated with these three different forms of intermingling. The mere existence of dual capable systems is not new— deploying such systems can increase the effectiveness of forces, and it can also provide more flexibility. The major powers have both employed and threatened with dual capable systems for decades, and they have done so without nuclear escalation. Similarly, the major powers co-located nuclear and conventional systems in the Cold War, and they did so for variety of reasons that had nothing to do with complicating the adversary’s risk calculus. The Soviet Union, for example, decided to co-locate its nuclear and conventional forces for economic and administrative reasons. Although today it might be recognized as a useful deterrent tool, it was not their primary intention. Major powers want to convince rivals that the co-location of forces creates a high bar for targeting and raises the risk of nuclear escalation, but they also want to have the flexibility of this not being true in an actual crisis or conflict.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗

DOE OSTI2025

Lattice Effective Field Theory Simulations of Nuclei

Lattice effective field theory applies the principles of effective field theory in a lattice framework where space and time are discretized. Nucleons are placed on the lattice sites, and the interactions are tuned to replicate the observed features of the nuclear force. Monte Carlo simulations are then employed to predict the properties of nuclear few- and many-body systems. Here, we review the basic methods and several theoretical and algorithmic advances that have been used to further our understanding of atomic nuclei.

nuclear lattice effective field theory↗

DOE OSTI2021

Boson Fermion Nucleus Polynuclear Structure: Monograph #11

The boson fermion nucleus (BFN) structure indicates the possibility of stable, nonradioactive polynuclear structures bound by the strong nuclear force. In the process of making polynuclear structures, BFN self-ordering on the nuclear level as a stable structure resembles the self-ordering of carbon atoms at the atomic level into buckminsterfullerene, graphene sheet, or graphene nanotubes. This natural assembly derives from the modulation of electron orbital collapse, which decreases coulomb repulsion between atoms and allows a natural reordering among nuclear structures by modulating the permeability of free space. Polynuclear material would be unearthly in tensile strength, thermal and electrical conductivity, and heat of disassociation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2023

White Paper On Nuclear Structure Reactions and Astrophysics

In preparation for the 2023 NSAC Long Range Plan (LRP), the DNP Town Meeting on Nuclear Structure, Reactions, and Astrophysics was held at Argonne National Laboratory (ANL) on Nov 14-16, 2022. The town meeting brought together 578 members of the low-energy nuclear science community, including 216 in-person attendees and 362 remote participants coming from US national laboratories, a wide range of US universities and other research institutions and universities abroad. Participants met in five topic-oriented and seven cross-cutting and intersecting working groups to discuss progress since the 2015 LRP and identify compelling science opportunities and the resources needed to realize them. These considerations were used during the Town Meeting to determine a set of resolutions outlining the highest priorities for our subfield. The full text of the resolutions endorsed by unanimous consent by the low-energy nuclear science community at the Town Meeting is presented at the end of this executive summary. The reports from all working groups that met during the Town Meeting are included as Secs. 1 to 11 of this Whitepaper. The intellectual challenges for nuclear structure, reactions and astrophysics can be captured in the following questions: What is the nature of the nuclear force that binds protons and neutrons into stable nuclei and rare isotopes, and how do the rich phenomena of nuclear structure and reactions emerge? How do single-nucleon, cluster, and collective degrees of freedom coexist and evolve with increasing proton-neutron imbalance and excitation energies? What are the limits of nuclear existence, and what features arise near and beyond these limits? What are the astrophysical origins of the elements and how did the associated chemical evolution proceed? How do stars evolve, and what nuclear signatures do they leave behind? What is the nature of neutron stars and dense matter? How can the knowledge and technological progress provided by nuclear science best be used to benefit society?

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2021

Measurement of Parity Violating Asymmetry in Elastic Electron Scattering off 48Ca

Atomic nuclei are composed of nucleons governed by the strong nuclear force. Although the proton distributions in nuclei are well measured with electromagnetic probes, the neutron distributions are relatively unconstrained. The nuclear symmetry energy governs the distribution of the excess neutrons in asymmetric nuclei, as well as the dynamics of neutron-rich nuclear matter up to the scale of neutron stars….

Clarke, Cameron↗

DOE OSTI2022

Theory of nuclear fission

Atomic nuclei are quantum many-body systems of protons and neutrons held together by strong nuclear forces. Under the proper conditions, nuclei can break into two (sometimes three) fragments which will subsequently decay by emitting particles. This phenomenon is called nuclear fission. Since different fission events may produce different fragmentations, the end-products of all fissions that occurred in a small chemical sample of matter comprise hundreds of different isotopes, including α particles, together with a large number of emitted neutrons, photons, electrons and antineutrinos. The extraordinary complexity of this process, which happens at length scales of the order of a femtometer, mostly takes less than a femtosecond but is not entirely over until all the lingering β decays have completed – which can take years – is a fascinating window into the physics of atomic nuclei. While fission may be more naturally known in the context of its technological applications, it also plays a crucial role in the synthesis of heavy elements in astrophysical environments. In both cases, simulations are needed for the many systems or energies inaccessible to experiments in the laboratory. In this context, the level of accuracy and precision required poses formidable challenges to nuclear theory. Overall, the goal of this article is to provide a comprehensive overview of the theoretical methods employed in the description of nuclear fission.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2026

Nuclear shell structure governs short-range nucleon pairing

Atomic nuclei are intricate quantum systems in which nucleons (protons and neutrons) are held together by the strong nuclear force. At very short distances, nucleons can momentarily form high-momentum pairs—known as short-range-correlated pairs—that shape the high-momentum structure of nuclear matter. Studying how nucleons form short-range-correlated pairs provides a rare experimental window into the short-distance behaviour of the strong interaction. Here, in this study, we use the scattering of high-energy electrons from 40 Ca, 48 Ca and 54 Fe, chosen for their distinct shell structures, to probe the formation of short-range-correlated pairs. Unexpectedly, we find that short-range-correlated pairing depends far more on the specific quantum orbitals occupied by protons and neutrons than on the nuclear mass or neutron–proton imbalance. This dependence is much stronger than that predicted by theoretical models. Our results point to a need for new angular-momentum quantum selection rules governing short-range nucleon pairing and reveal a deep connection between long-range nuclear shell structure and short-range interactions.

Nguyen, D. [Thomas Jefferson National Accelerator ↗

DOE OSTI2025

Global Framework for Emulation of Nuclear Calculations

We introduce a hierarchical framework that combines ab initio many-body calculations with a Bayesian neural network, developing emulators capable of accurately predicting nuclear properties across isotopic chains simultaneously and being applicable to different regions of the nuclear chart. We benchmark our developments using the oxygen isotopic chain, achieving accurate results for ground-state energies and nuclear charge radii, while providing robust uncertainty quantification. Our framework enables global sensitivity analysis of nuclear binding energies and charge radii with respect to the low-energy constants that describe the nuclear force.

FOS: Computer and information sciences↗

DOE OSTI2025

Why Do Nuclei Stick Together?

Although quantum chromodynamics (QCD) has long been accepted as the underlying theory of the strong nuclear force, connecting the structure and interactions of nuclei to the fundamental parameters of QCD remains challenging. In this talk, I will present new results from lattice QCD and effective field theory that explore how nuclear interactions look in a world where the quarks are much heavier than they are in nature, and discuss lessons that can be learned for nuclear physics as well as searches for physics beyond the Standard Model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Twentieth Exotic Beam Summer School (EBSS2023)

The study of unstable nuclei with unusual ratios of protons to neutrons is one of the frontiers of science. Investigating these rare isotopes is critical for understanding the synthesis of the chemical elements in stellar explosions as well as the fundamental nature of the nuclear forces that bind atomic nuclei together. Scientific progress in this field is driven by the development of exotic beams in present and next-generation rare-isotope beam facilities including the Facility for Rare Isotope Beams (FRIB). Nuclear physics is a broad discipline, influencing our knowledge on subjects as diverse as weakly-bound nuclei, many-body quantum theory, the super heavy elements, and the inner structure of neutron stars. Applications based on nuclear science and technologies include medical diagnostics and therapies, materials science, and national security. The major goal achieved in this project was to hold Exotic Beam Summer School 2023 (EBSS2023), the twentieth installment of EBSS series, July 9-15, 2023 at the Facility for Rare Isotope Beams on the campus of Michigan State University to educate and train the next generation of scientists that will drive research with rare-isotope beams. FRIB became operational in 2022 and is now providing beams of exotic nuclei that will ramp up to unmatched intensities, exceeding what is available today by orders of magnitude. Beams available at FRIB are facilitating a wide variety of studies in nuclear structure, astrophysics, fundamental symmetries and societal applications. There is a large community of scientists interested in working with rare isotope beams; for example, the FRIB User Organization currently has over 1,700 members. In order to maximize the scientific output of FRIB, there must be a workforce continuously trained in both the physics of exotic beams and in the practical techniques of carrying out an experiment. This summer school series is designed to specifically address this need - to ensure that new generations of scientists from a broad range of institutions and backgrounds is trained, motivated, and equipped to push the field forward to new and important breakthroughs.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2026

Mapping the Gap: Analysis of Nuclear Cybersecurity Education in U.S. Universities

The U.S. nuclear sector is undergoing rapid transformation, driven by the expansion of advanced reactors, digital modernization of legacy systems, and increasing interest in nuclear energy to meet AI-fueled energy demands. However, the cybersecurity talent pipeline is not keeping pace with this growth. This paper investigates the significant gap in nuclear cybersecurity education and proposes scalable strategies for colleges to address this critical need by promoting it as a viable and essential career path. Through a multi-institutional landscape analysis of 16 cybersecurity and 12 nuclear engineering programs, we found that nuclear cybersecurity is largely absent from university curricula. Most students are unaware of the field’s existence, and few institutions offer hands-on training or interdisciplinary exposure. This lack of awareness leads to a shortage of specialized talent, forcing nuclear facilities to retrain generalist hires or rely on costly external consultants. We present a framework for early pipeline cultivation grounded in Social Cognitive Career Theory and workforce development principles. Proposed solutions include student-led clubs, guest lectures, modular classroom kits, and summer boot camps. By increasing visibility and access to nuclear cyber content, we aim to break the self-reinforcing cycle of low awareness and limited specialization. This work underscores the critical role of education and advocacy in cultivating early interest and guiding students toward this emerging field. We call on academic institutions, national laboratories, and industry stakeholders to collaborate in establishing nuclear cybersecurity as a distinct and accessible career path within the broader cybersecurity and nuclear engineering ecosystems.

99 - GENERAL AND MISCELLANEOUS↗

DOE OSTI2022

The Strategic Implications of the Evolving US-China Nuclear Balance

China is significantly expanding the size and sophistication of its nuclear forces. Over the summer of 2021, researchers using satellite imagery discovered three separate fields of intercontinental ballistic missile (ICBM) silos under construction in the deserts of north-central China. If each silo is eventually equipped with a missile, the Chinese nuclear arsenal capable of striking the continental US could triple in size. Furthermore, the US government estimates that China’s nuclear arsenal could number 1000 warheads by 2030, with at least 200 deployed on long-range platforms.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗

DOE OSTI2025

EIC Physics from Lattice QCD: investigations beyond leading twist

This project proposes theoretical studies of Quantum Chromodynamics (QCD), the theory describing the strong nuclear force among the building blocks (quarks and gluons) of the visible matter. These appear only confined within hadrons, that make up more than 99% of the mass of the matter. Understanding QCD will significantly advance many aspects of science, from the sub-nuclear interactions to astrophysics, and a quantitative theoretical description is imperative. However, this is a challenging task because QCD is a highly nonlinear theory. We propose hadron structure calculations within lattice QCD (LQCD), an ideal ab initio approach based on space-time discretization, which allows the study of the properties of fundamental particles numerically. This is done by defining the continuous equations on a discrete four-dimensional lattice, which results in equations with hundreds of billions of degrees of freedom, and must be simulated in powerful computers.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2022

The Equation of State of Neutron-Rich Matter at Fourth Order of Chiral Effective Field Theory and the Radius of a Medium-Mass Neutron Star

We report neutron star predictions based on our most recent equations of state. These are derived from chiral effective field theory, which allows for a systematic development of nuclear forces, order by order. We utilize high-quality two-nucleon interactions and include all three-nucleon forces up to fourth order in the chiral expansion. Our ab initio predictions are restricted to the domain of applicability of chiral effective field theory. However, stellar matter in the interior of neutron stars can be up to several times denser than normal nuclear matter at saturation, and its composition is essentially unknown. Following established practices, we extend our microscopic predictions to higher densities matching piecewise polytropes. The radius of the average-size neutron star, about 1.4 solar masses, is sensitive to the pressure at normal densities, and thus it is suitable to constrain ab initio theories of the equation of state. For this reason, we focus on the radius of medium-mass stars. We compare our results with other theoretical predictions and recent constraints.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2025

Quantifying uncertainties in α -nucleus reaction dynamics informed from first principles

The ab initio symmetry-adapted no-core shell model is a microscopic many-body method which naturally describes challenging collective and clustering features of atomic nuclei. Wave functions and observables computed with realistic nucleon-nucleon forces in this framework are tied to first principles, and are hence well-suited for rigorous uncertainty quantification. We discuss α-deuteron and α- 12 C cluster potentials informed by symmetry-adapted calculations, and propagate uncertainties in the effective binary cluster method as well as those in the nuclear interaction to reaction observables, namely scattering phase shifts, cross sections, partial widths and resonance energies. Here, we find that the overall uncertainties are dominated by those originating in the underlying nuclear force, speaking to the need for tighter constraints on realistic nucleon-nucleon interactions.

Ab initio↗

DOE OSTI2024

Imaging shapes of atomic nuclei in high-energy nuclear collisions

Atomic nuclei are self-organized, many-body quantum systems bound by strong nuclear forces within femtometre-scale space. These complex systems manifest a variety of shapes, traditionally explored using non-invasive spectroscopic techniques at low energies. However, at these energies, their instantaneous shapes are obscured by long-timescale quantum fluctuations, making direct observation challenging. Here we introduce the collective-flow-assisted nuclear shape-imaging method, which images the nuclear global shape by colliding them at ultrarelativistic speeds and analysing the collective response of outgoing debris. This technique captures a collision-specific snapshot of the spatial matter distribution within the nuclei, which, through the hydrodynamic expansion, imprints patterns on the particle momentum distribution observed in detectors. We benchmark this method in collisions of ground-state uranium-238 nuclei, known for their elongated, axial-symmetric shape. Our findings show a large deformation with a slight deviation from axial symmetry in the nuclear ground state, aligning broadly with previous low-energy experiments. This approach offers a new method for imaging nuclear shapes, enhances our understanding of the initial conditions in high-energy collisions and addresses the important issue of nuclear structure evolution across energy scales.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

First Measurement of the Isospin-Dependence of Nuclear Structure Functions at 12 GeV Jefferson Lab

The structure functions of protons and neutrons provide crucial insight into how the strong nuclear force, as described by Quantum Chromodynamics (QCD), manifests at everyday energies, allowing us to better understand precisely how quarks and gluons interact to form the basic building blocks of almost all visible mass in our universe. Despite more than 40 years of experimental and theoretical effort, the EMC effect – the observation that nuclear structure functions appear to be modified from those of free nucleons – is still not fully understood. One open question that remains is whether or not the modification of quark distributions is the same for all quark flavors. Determining the flavor (isospin) dependence of the EMC effect, which is predicted by several models, is essential for coming to a complete understanding of how QCD manifests in nuclei. To this end, inclusive electron Deep Inelastic Scattering (DIS) from nuclei with approximately constant atomic mass number A and variable proton-to-neutron ratio N/Z was measured in Jefferson Lab experiment E12-10-008 to look for isospin-dependent modification of nuclear structure functions. The preliminary EMC ratios presented here cover a kinematic range of 2.8 < Q2 < 8.1 GeV2 and 0.18 < xBj < 1.0. The size of the EMC effect in these nuclei is extracted by calculating the slope of the EMC ratio as a function of Bjorken x (xBj ) over the ranges 0.3 < xBj < 0.6 and 0.3 < xBj < 0.7; these slopes then are compared with existing world data. Our preliminary results do not appear to indicate significant isospin-dependence of the EMC effect, though a more careful study is needed once all results are confirmed.

Cotton, Cameron William [Univ. of Virginia, Charlo↗