Heavy Elements from Neutron Star Mergers: Progress and Puzzles

In the aftermath of a neutron star merger, matter from the torn apart stars is expected to gradually drain into the central remnant (a black hole), powering relativistic jets and sub-relativistic outflows. In 2017, follow-up of the gravitational wave source GW170817 confirmed this picture — detection of a coincident gamma-ray burst (GRB) provided evidence for a relativistic jet, while optical/infrared emission indicated slower outflows composed of radioactive heavy isotopes (an event called a kilonova). Observations of this kilonova provided the first direct evidence that heavy nuclei are synthesized via the r-process in mergers. Since that time, there have been a disappointingly few gravitational wave detections of neutron star mergers, and none with electromagnetic counterparts. However, some interesting (if confusing) results have recently emerged in studies of GRBs without gravitational wave data. A handful of new GRBs show what looks like signs of r-process emission, but the duration of the GRB is much longer than expected and the spectra of the kilonova different than predictions. I will review the physics at play, and discuss how theoretical modeling can help determine whether these new events are really additional examples of r-process nucleosynthesis in mergers, or instead are something altogether different, such as collapsing massive stars or disrupted white dwarfs.

Rational Design and Application of Organic-Based Scintillators

Organic scintillators are widely used as radiation detection media in diverse application areas, including homeland security and nuclear physics. This is due to the potential for large-scale and low-cost detectors to directly detect fast neutrons, gamma-rays, and other types of ionizing radiation. However, several challenges remain at the intersection of detection performance, cost, scale, and physical characteristics. In this colloquium, I will describe the interplay between these factors and a pathway towards the rational design of these materials. A case study in Organic Glass Scintillator (OGS)-based materials will be provided as a template for future material development efforts. Also to be discussed will be the configuration of OGS scintillators into optically segmented and waveguide detectors for spatially- and time-resolved applications.

How strong are the strong interactions?

Modern particle physics experiments, e.g. at the Large Hadron Collider (LHC) at CERN, crucially depend on the precise description of the scattering processes in terms of the known fundamental forces. This is limited by our current understanding of the strong nuclear force, as quantified by the strong coupling, ⍺S, between quarks and gluons.  Relating ⍺S to experiments poses a major challenge as the strong interactions lead to the confinement of quarks and gluons inside hadronic bound states. At high energies, however, the strong interactions become weaker (``asymptotic freedom’’) and thus amenable to an expansion in powers of the coupling.  Attempts to relate both regimes usually rely on modeling of the bound state problem in one way or another.  In this talk I will go over 25 years of theoretical advances that have made possible to determine ⍺S without relying on models for the physics at low energies. These techniques, based on Lattice QCD and large scale lattice simulations, are able to produce precise determinations of the strong coupling with negligible theoretical uncertainties. This result will increase the likelihood to uncover small effects of yet unknown physics, and enable stringent precision tests of the Standard Model.

Pushing Boundaries: Advancements in Heavy Element Synthesis and Radiation Effects Research at the 88-Inch Cyclotron

The 88-Inch Cyclotron supports ongoing research programs in heavy element studies, nuclear data for societal needs, and technology R&D. Efforts to synthesize elements beyond oganesson (Z=118) will push the limits of current technology due to the expected low production cross sections (below the 100 femtobarn level) and short half-lives (likely of order a few microseconds) for these elements. The approach to making new elements necessitates using beams other than 48Ca. The ion source group at the 88-Inch Cyclotron has developed a Ti beam, which, combined with a Cf target, could produce a new element, Z=120. The Ti beam was created using VENUS and AECR ion sources and new oven technologies. The 88-Inch Cyclotron plans to host a new element search involving long running periods (many months) of intense beams (~1 particle μA 50Ti) on actinide targets to approach the theoretical tens of femtobarn production cross sections. On the applications side, the 88-Inch Cyclotron provides a unique environment for conducting radiation effects testing at the Berkeley Accelerator Space Effects (BASE) Facility, providing well-characterized beams of protons, heavy ions, and other medium energy particles to simulate the space environment. The National Security Space (NSS) community and researchers from other government, university, commercial, and international institutions use these beams to understand the effect of radiation on microelectronics, optics, materials, and cells.

BAR: Bayesian Analyses of Reactions

Nuclear reactions are an essential probe for studying isotope structure and nuclear astrophysics.

It is from nuclear reactions that we learn about where nuclei come from and how they are produced. Also, reaction experiments provide critical knowledge on how neutrons and protons organize themselves to form matter as we know it and matter at the limits of stability.

However until recently, models for nuclear reactions included no uncertainty quantification. In this presentation, I will review the Bayesian analysis efforts developed over the last 6 years in reaction theory, including not only uncertainty quantification but also steps toward experimental design. This presentation assumes no prior knowledge on Bayesian Statistics.

Some relevant references:

[1] C. Hebborn et al., J. Phys. G 50, 050601 (arXiv:2210.07293)

[2] G.B. King et al., Phys. Rev. Lett. 122, 232502 (2019)

[3] A. Lovell et al., J. Phys. G 48, 014001 (2020)

[4] M. Catacora-Rios et al., Phys. Rev. C 100, 064615 (2019)

[5] T. Whitehead et al., Phys. Rev. C 105, 054611 (2022)

[6] M. Catacora-Rios et al., Phys. Rev. C 108, 024601 (2023)  (arXiv:2212.10698)

[7] M. Catacora-Rios et al., Phys. Rev. C 104, 064611 (2021)

Design of first experiment to achieve fusion target gain > 1

The inertial fusion community have been working towards ignition for decades, since the idea of inertial confinement fusion (ICF) was first proposed by Nuckolls, et al., in 1972. On August 8, 2021 and Dec 5th 2022, the Lawson criterion for ignition was met and more fusion energy was created than laser energy incident on the target at the National Ignition Facility (NIF) in Northern California. The first experiment produced a fusion yield of 1.35 MJ from 1.9 MJ of laser energy and appears to have crossed the tipping-point of thermodynamic instability according to several ignition metrics.  Building on this result, improvements were made to increase the fusion energy output to ~4MJ from 2.05 MJ of laser energy on target, resulting in target gain exceeding unity for the first time in the laboratory.  This result is important in that it proves that there is nothing fundamentally limiting controlled fusion energy gain in the laboratory.  The presentation will detail the changes made to achieve this result.

Bio and photo are attached.