Understanding astrophysical observables and phenomena requires a thorough knowledge of various properties of nuclei all over the nuclear chart. Since most of these systems are inaccessible through experiment, theoretical predictions are necessary. At present, nuclear Density Functional Theory is the only method available which can reach these systems while maintaining a microscopic character. Its key ingredient, the nuclear energy density functional, is an effective interaction based on one-body local densities and currents which contains a number of coupling constants whose values are optimized to experimental data and/or pseudo-data. Developing this interaction to minimize its root-mean-square error with respect to certain observables is crucial for more accurate astrophysical predictions. Past and current procedures in this endeavor will be discussed, as well as future plans to incorporate beyond-mean-field effects through both the cranking model and the generator coordinate method, as well as different approaches to the statistical fitting of the functional.

Committee: Kenji Saito(Chairperson), Morten Hjorth-Jensen, Chong-Yu Ruan, Jie Wei, Yoshishige Yamazaki. Thesis is on display in 1312 BPS Bldg. and NSCL Atrium

Short-range correlations (SRC) are pairs of strongly interacting nucleons at close proximity. Due to their large spatial overlap and high relative-momentum, the study of SRC pairs is an appealing gateway for probing the strong nuclear interaction at high-densities (i.e. short-distances) and its relation to the underlaying quark-gluon substructure of nuclei. In this talk I will present new results from high-energy electron scattering experiments that probe SRC pairs via measurements of exclusive hard breakup reactions. Special emphasis will be given to the effect of SRCs on the behavior of protons in neutron-rich nuclear systems and how it can impact properties of dense nuclear systems such as neutron stars. Pursuing a more fundamental understanding of short-distance interactions, I will present new measurements of the internal quark-gluon sub-structure of nucleons and show how its modification in the nuclear medium relates to SRC pairs and short-ranged nuclear interactions. Last, I will also discuss the development of new effective theories for describing short-ranged correlations, the way in which they relate to experimental observables, and the emerging universality of short-distance and high-momentum physics in nuclear systems.

The use of particle accelerators has a long history at Los Alamos National Laboratory (LANL), from their early use in radiography to their present day use in stockpile stewardship. There are two primary accelerator system in use today at LANL, LANSCE (the Los Alamos Neutron Science Center) and DARHT (the Dual-Axis Radiographic Hydrodynamic Test facility), and they are heavily subscribed. Recently, LANL formulated an overall laboratory accelerator strategy, and this strategy highlights both the need to maintain our current capabilities, but to also expand these capabilities to meet the ever evolving mission need. Following a summary of the history of accelerators at LANL, current systems and uses will be described. This will be followed with our vision of the future for accelerator systems at LANL.

The radiation from rare isotopes allows us to detect them, but it also marks their decay. Radiochemists are constantly racing against the clock to utilize the traceability of radionuclides to improve our understanding of chemistry, medicine, physiology, nuclear physics, and many other interesting subjects. Sometimes too-short or too-long half-lives make that job difficult, and require us to mix and match elements outside of their natural environments. The plus side of that rearrangement is that radiochemists get to work with elements all across the periodic table. Who else plays with manganese, lanthanum, zirconium, thulium, and erbium all in the same week? Come see how fast and slow decays are used to trace all types of interesting processes with the most unlikely combination of elements.

Fission and nucleosynthesis

The astrophysical site(s) for the rapid neutron capture process which synthesizes the heaviest elements observed in nature has been a long outstanding question. The era of multi-messanger astronomy now permits unprecedented insights into astrophysical events, as evidenced by LIGO/VIRGO's ability to direct the telescope community to perform detailed electromagnetic follow-up for merger events such as GW170817. Nuclear physics experiment is simultaneously undergoing its own era of revolution by beginning to probe the very neutron-rich regions populated at crucial times during the r process, as is being done by the CPT at CARIBU. The next generation of nuclear physics experiment will push the boundary of explored nuclei even further. FRIB will produce hundreds of neutron-rich species for the first time, making them accessible for numerous studies which determine properties such as masses or beta-decay half-lives. But what exactly do these revolutions in experiment and observation mean for our understanding of the origin of the heaviest elements in our galaxy? The r-process nucleosynthesis studies I will present explicitly connect these avenues of exploration via considering how nuclear data influences r-process observational signatures. We will discuss the current uncertainties affecting r-process calculations and how these will be reduced by next generation experiments. Since the electromagnetic signal from merger events is highly influenced by the presence of high opacity lanthanide elements, we will focus our discussion on a feature of enhanced lanthanide production, the r-process rare-earth abundance peak, which could be intimately linked to the nuclear structure and deformation of neutron-rich lanthanide species. The alternative means by which the rare-earth peak can be produced is via late-time fission deposition which we will also examine in the context of new theoretical fission yields for neutron-rich nuclei. The question of where nature primarily produces the heavy elements can only be answered through such collaborative efforts between theory, experiment, and observation.

The exciting physics of neutron-rich matter covers a wide range of densities, from finite nuclei to neutron stars. Constraining the neutron-rich matter equation of state (EOS) simultaneously from experiment, observation, and theory is a very active field of research. In anticipation of novel constraints, e.g., from FRIB and multi-messenger astronomy, it is time to take advantage of the recent advances in chiral effective field theory (EFT) and many-body frameworks to improve microscopic predictions of the EOS based on chiral nuclear interactions. I will discuss several applications of a novel Monte Carlo framework for many-body perturbation theory to infinite nuclear matter with chiral two-, three-, and four-nucleon interactions. The efficiency of this framework allows for the incorporation of all many-body contributions up to high orders as well as the Bayesian estimation of theoretical uncertainties through order-by-order calculations. I will show results for the EOS of neutron and symmetric matter, the nuclear saturation point, the symmetry energy as well as its slope parameter, and a comparison to results based on quark-gluon degrees of freedom at intermediate densities. Nuclear matter is furthermore an ideal testbed for the development of chiral interactions aimed at precise nuclear structure and reaction calculations with quantifiable uncertainties across a wide range of the nuclear chart. As a first step, we fit chiral interactions up to next-to-next-to-next-to-leading order (N3LO) to the triton as well as the empirical saturation point. Such approaches have recently gained much attention since ab initio calculations of medium-mass to heavy nuclei have demonstrated that realistic saturation properties of chiral forces in infinite matter are important for reproducing experimental ground-state energies and charge radii. I will review our subsequent study of closed-shell medium-mass nuclei up to nickel using the ab initio In-Medium Similarity Renormalization Group (IM-SRG) and my conclusions for making progress in this direction.

In the mid-eighties, the development of radioactive-ion beams has enabled the study of nuclei far from stability. This technical breakthrough has led to the discovery of nuclei which display unexpected structures, challenging the usual description of nuclear matter. In particular, in the neutron-rich region, halo nuclei have been observed. These nuclei exhibit a very large matter radius compared to their isobars. Since they are short-lived, they cannot be studied through the usual spectroscopic techniques but they are mostly probed with reactions, such as elastic scattering, breakup and knockout. To extract precise information from these measurements, an accurate reaction model coupled to a realistic description of the nucleus is needed. The eikonal model is reliable at high energies, i.e., above 60 MeV/nucleon, and has a short computational time. During this seminar, I will present three different projects on the eikonal model that I have conducted during my PhD. My first project is the extension of the eikonal model to lower energies, i.e., 10 MeV/nucleon, in the energy range of the new facilities ReA12 at FRIB and HIE-ISOLDE at CERN. To improve the eikonal model at low energies, I have studied corrections to the nuclear deflection of the projectile by the target. I have assessed their efficiency for the elastic scattering and breakup of one-neutron halo nuclei. My second research topic is the development of an eikonal-like model which treats at the first-order the dynamics of the projectile during the collision. This new model has a similar numerical cost as the eikonal model but does not diverge for the Coulomb breakup, since it corrects for the adiabatic approximation. My third research is on knockout reactions and which nuclear structure information can be inferred from such measurements. To identify what can be probed with such reactions, I have used a halo effective-field theory to describe the projectile. Finally, I will present my research plans for the FRIB-Theory Fellowship. My idea is to bridge reaction theory with ab initio theory through the development of optical potentials from the no-core shell model with continuum calculations.

Nuclear reactions generate energy in nuclear reactors, in stars, responsible for the existence of all elements heavier than Hydrogen in the universe and provide information of nuclear structure. An important mechanism that takes place in the nuclear collisions is the dissociation of the projectile into two or more fragments. For the two-body dissociation, this corresponds to reactions of the form a(=b + x) + A -> b + x +A. The theoretical interpretation of these reactions is studied by Faddeev and later reformulated by Alt-Grassberger- Sandhas (AGS) in momentum space. In this talk, I will discuss about solving the Faddeev-AGS equation with separable form interactions which have the advantages to include the Coulomb interaction exactly. In addition, I will also discuss about the inclusive breakup, which takes the form a+A-> b + anything, and several applications based on the studies of inclusive breakup.

The abundance of lithium observed in very young stellar populations is few times larger than the primordial one estimated by recent Planck measurements. Since Lithium is easily destroyed in the stellar interiors, the search for astrophysical sources responsible for the observed lithium over-abundance was a challenge for decades. In this talk I will present the results of an on-going survey dedicated to the study of nova outburst with high-resolution spectrographs at ESO/VLT. In particular, I will concentrate on the recent detection of beryllium-7 in the spectra of recent classical novae. While this finding is a further confirmation of the occurrence of the thermo-nuclear runaway in nova explosions, at same time it implies that classical novae are one of the main factories of lithium in our Galaxy (and other nearby systems).