Measuring Neutron Skins in Neutron-Rich Nuclei with PREX and CREX (Junior Workshop (May 21 - 22))

• Brendan Reed (IU Bloomington)

The structure of the atomic nucleus is governed by the equation of state (EOS) of nuclear matter. For neutron-rich nuclei, the equation of state for neutron matter is constrained by a number of electroweak experiments. Recently, the PREX and CREX experiments have measured the neutron skin Rn-Rp of the neutron-rich $^{208}$Pb and $^{48}$Ca, respectively. PREX determined a moderately large neutron skin in $^{208}$Pb, which suggests a moderately stiff EOS. However CREX determined a very small neutron skin in $^{48}$Ca which suggests a soft EOS. This discrepancy paints a rather peculiar picture of neutron-rich matter. In this talk, I will discuss the implications of both experimental results on dense neutron-rich matter, including the connection to neutron stars and gravitational waves.

Dependence of ( n , γ ) − ( γ , n ) equilibrium r -process abundances on nuclear physics properties

• Mengke Li

In most r-process expansions, the dominant nuclear evolution occurs in an (n, gamma)-(gamma, n) equilibrium in which nuclei rapidly exchange neutrons but change charge much more slowly by beta decay. Freeze-out from this equilibrium shapes the final abundances but does not significantly alter the overall global abundance pattern; therefore, it is important to understand the details of (n, gamma)-(gamma, n) equilibrium both because it is the main evolution phase that determines the final abundance pattern and because it is the starting point for the freeze-out. Through use of a simple but realistic phenomenological nuclear physics model, we show that isotopic abundances versus neutron number in (n, gamma)-(gamma, n) equilibrium are well approximated as Gaussians. Nuclear pairing causes isotopic abundances to alternate between two Gaussians, and shell effects cause the isotopic abundances to shift from one Gaussian to another when the neutron number crosses a magic number. More complex neutron-separation energy curves versus mass number can be generated by adding a spike function to a linearly declining curve. In such a case, the equilibrium abundance curve jumps from one Gaussian to another for each added spike. Insights from our model can help shed light on how detailed theoretical or experimental nuclear data affect r-process nucleosynthesis during the (n, gamma)-(gamma, n) equilibrium phase.

The early evolution of magnetars

• Tejas Prasanna (The Ohio State University)

In the seconds following their formation in core-collapse supernovae, proto-magnetars drive neutrino-heated magneto-centrifugal winds. Using a suite of two-dimensional axisymmetric MHD simulations, we show that relatively slowly rotating magnetars with initial spin periods of 50-500 ms and polar magnetic field strength of about $10^{15}$ G spin down rapidly to periods greater than 1 s during the neutrino Kelvin-Helmholtz cooling epoch which lasts for about 10-100 s. Since the flow is non-relativistic at early times, and because the Alfven radius is much larger than the proto-magnetar radius, spindown is millions of times more efficient than the typically-used dipole formula. Quasi-periodic plasmoid ejections from the closed zone enhance spindown. We discuss the implications for observed magnetars, including the discrepancy between their characteristic ages and supernova remnant ages. We also speculate on the origin of 1E 161348-5055 in the remnant RCW 103, and the potential for other ultra-slowly rotating magnetars. On the other hand, we show that rapidly rotating magnetars with initial spin period of less than 5 milliseconds and strong magnetic fields greater than $10^{15}$ G are viable central engines for producing gamma-ray bursts. Millisecond magnetars with moderate magnetic field strengths of about $10^{14}$ G can power super-luminous supernovae.

Hydrogen-Triggered Thermonuclear X-ray Bursts

• Sierra Casten (Michigan State University)

Type I X-ray bursts are caused by the unstable ignition of H and/or He that has accreted onto the surface of a neutron star in a binary system. As matter accumulates on the surface, the temperature and pressure at the base of the accreted layer increase until thermonuclear reactions ignite. At very low accretion rates, it is possible that thermally unstable hydrogen burning does not raise the envelope temperature sufficiently to trigger unstable helium burning and therefore produces only a weak, purely H-powered burst. We present a study of weak, thermonuclear X-ray bursts from the accreting millisecond X-ray pulsar SAX J1808.4-3658. We primarily focus on a burst observed with the Neutron Star Interior Composition Explorer in 2019 August but also describe a similar burst observed with Rossi X-ray Timing Explorer in 2005 June. We measure peak burst bolometric fluxes that are factors of approximately 30 and 15 less than the peak flux of the brightest, helium-powered bursts observed from this source. The low accretion rates, inferred low ignition masses, and evidence that the neutron star interior is cold, suggest these bursts are triggered by thermally unstable CNO cycle hydrogen burning. The post-burst flux level in the 2019 event appears offset from the pre-burst level by an amount consistent with quasi-stable hydrogen burning due to the temperature-insensitive, hot-CNO cycle, further suggesting hydrogen burning as the primary fuel source. This provides strong observational evidence for hydrogen-triggered bursts. Comparing these observations with theoretical models provides interesting constraints on the accretion rate, nuclear heating, neutrino cooling, and heat transport in the neutron star interior.

A GADGET for Nova Nucleosynthesis Studies

• Tamas Budner (Michigan State University)

The Gaseous Detector with Germanium Tagging (GADGET) was developed at Michigan State University to measure weak, low-energy, $\beta$-delayed, charged-particle decays in service of determining thermonuclear reaction rates that are relevant for modeling explosive nucleosynthesis. GADGET has been successfully employed in multiple exotic beam experiments, including $^{23}$Al and $^{31}$Cl $\beta^+$ decay measurements. The decays of these neutron-deficient nuclei selectively populate crucial resonances for the radiative proton-capture reactions $^{22}$Na($p,\gamma$)$^{23}$Mg and $^{30}$P($p,\gamma$)$^{31}$S, respectively. Both reactions are important for understanding observables associated with classical nova events, including their range of detectability via $\gamma$-ray astronomy, the peak temperatures achieved during thermonuclear runaway, as well as isotopic ratios in certain presolar grains. GADGET's record sensitivity for detecting weak, $\beta$-delayed proton decays below 400-keV resonance energies has further constrained the thermonuclear rates of interest, whose effects on the nuclear abundances within nova ejecta were investigated using state-of-the-art hydrodynamic simulations. Here, we present the scientific findings of these nova nucleosynthesis studies and invite discussion of potential future prospects for both the original GADGET system as well as its upgraded functionality as a time projection chamber. This work was supported by the National Science Foundation under Grants PHY-1913554, No. PHY-1102511, No. PHY-1565546, PHY-2110365, No. PHY-2011890; the Department of Energy Office of Science under Award No. DE-SC0016052; the Natural Sciences and Engineering Research Council of Canada (NSERC); the Spanish MINECO grant PID2020-117252GB-I00, the E.U. FEDER funds, the AGAUR/Generalitat de Catalunya grant SGR-386/2021, the EU Horizon 2020 Grant No. 101008324; and Korean NRF Grants No. 2020R1A2C1005981 and No. 2016R1A5A1013277.

Understanding the nuclear processes on proton-rich side of nuclear chart through synthesis of 196Hg and 26Si(α, p)29P reaction (Junior Workshop (May 21 - 22))

• Kushi Bhatt (Western Michigan University)

The p-nuclei (proton-rich nuclei) are among the rarest of all the known stable nuclei. Most nuclei heavier than iron are produced through neutron capture processes, but p-nuclei are not thought to be produced via neutron-capture. The astrophysical processes responsible for the synthesis of p-nuclei are not fully understood yet. There are 35 known p-nuclei and the heaviest known is $^{196}$Hg. Its synthesis is studied through the method of activation using (p, 𝛾), (p, n) and (p, α) reactions in energy range of 4-6.93 MeV. A mono-energetic proton beam is incident on a solid HgS target (thickness ~10mg/cm$^2$) made using the method of drop-casting. To further understand the nuclear processes on the proton-rich side of the nuclear chart, the $^26$Si(α, p)$^29$P reaction has been found to be an important reaction for the nucleosynthesis in type 1 X-ray bursts. Ongoing work for the production and optimization of $^26$Si beam using RAISOR (Argonne In-Flight Radioactive Ion Separator) and Machine Learning techniques will also be presented.

Measurement of the radiative branching ratio of the Hoyle state in $^{12}{\rm C}$ carried out with magnetic selection

• Zifeng Luo (Texas A&M University)

Room: Rm 1300 - Auditorium The triple-alpha process is a fundamental reaction in nuclear astrophysics, involving two consecutive reactions: $\alpha+\alpha\to^{8}{\rm Be}$ followed by $^{8}{\rm Be}+\alpha\Leftrightarrow\gamma+^{12}{\rm C}$, which ultimately leads to the formation of carbon. The latter reaction proceeds through a specific excited $0^{+}$ state known as the Hoyle state, located at 7.65 MeV excitation energy in $^{12}{\rm C}$. The reaction rate of the triple-alpha process is primarily determined by the radiative width $\Gamma_{\rm rad}$, which can be estimated from the branching ratio for electromagnetic decay and the known partial width $\Gamma_{\pi}(E0)$ for electron-positron pair production. However, a recent measurement of $\Gamma_{\rm rad}$ deviates from the currently adopted value by more than $3\sigma$, motivating us to conduct further investigation. In this study, we aim to verify the recent measurement by measuring the total radiative decay branching ratio of the Hoyle state in $^{12}{\rm C}$ using the MDM spectrometer. To this end, we populated the Hoyle state via $^{12}{\rm C}+\alpha$ inelastic scattering, with the scattered $\alpha$-particles detected by a ΔE-E telescope and the heavy $^{12}{\rm C}$ recoils detected by the newly developed MDM-TexPPAC system. We utilized time-of-flight technology and track reconstruction to accurately identify the decay products of $^{12}{\rm C}$(7.65). Our experimental results will be presented at this meeting.

Progress towards Resonance Energy and Partial Widths Determination of the 15N(α, γ)19F at Ecm = 1323 keV

• Ruoyu Fang (University of Notre Dame)

Room: Rm 1300 - Auditorium The cosmic origin of Fluorine is still a debated and uncertain topic. The only stable isotope 19F has been observed in the Asymptotic Giant Branch (AGB) stars. 15N(α, γ)19F is considered to be the primary production reaction in AGB stars. The broad resonance at Ecm = 1323 keV contributes to the production rate of 19F at relevant temperatures. However, recent measurements show both energy and partial width discrepancies for this resonance. Here at the Nuclear Science Laboratory at the University of Notre Dame, we performed a solid TiN target measurement to investigate these discrepancies. Preliminary results will be presented in this talk.

Determining the Structure of Exotic Atomic Nuclei for Astrophysical Explosions

• Nisha Singh (Ohio University)

Our understanding of reactions in extreme conditions, such as in massive stars and X-ray bursts, is limited by nuclear physics uncertainties in quantities such as nuclear reaction rates. The poorly constrained nuclear reaction rates can impact the modeling of these astrophysical phenomena. Investigating these reaction rates will not only improve the precision of the model calculations but also promote the understanding of matter in extreme conditions. The Hauser-Feshbach (HF) statistical reaction model is one of the tools which describes reaction rates, where inputs like the nuclear level density play an important role. Two of the astrophysically important reactions are 24Mg(alpha, gamma)28Si and 59Cu(p, gamma)60Zn. Hence constraining their reaction rates to remove possible uncertainties is necessary. We performed 27Al(d, n) 28Si neutron evaporation spectrum measurements at the Edwards Accelerator Laboratory at Ohio University to constrain the nuclear level density of 28Si, which is the main input parameter in HF calculations of the 24Mg(alpha, gamma)28Si reaction rate. I will present the results of this study and briefly discuss ongoing work to upgrade our set-up with coincident charged-particle spectroscopy. This upgrade will enable the measurements of both the level density and the spin distribution in 60Zn to constrain these parameters for 59Cu(p, gamma)60Zn reaction rate calculations. Constraining these reaction rates will help to improve the precision of model calculations and our understanding of the behavior of matter in astrophysical environments.

The Neutron Mean Life and Big Bang Nucleosynthesis

• Tsung-Han Yeh (TRIUMF)

We explore the effect of neutron lifetime and its uncertainty on standard big-bang nucleosynthesis (BBN). BBN describes the cosmic production of the light nuclides $^1$H, D, $^3$H+$^3$He, $^4$He, and $^7$Li+$^7$Be in the first minutes of cosmic time. The neutron mean life $\tau_n$ plays a key role in determining the amount of free neutrons when BBN starts. Almost all free neutrons are locked into $^4$He during BBN while the other light isotopes are produced in trace amounts compared with $^4$He. We present a study of the sensitivity of the light element abundances to the modern neutron lifetime measurements. We find that $\tau_n$ uncertainties dominate the predicted $^4$He error budget, but these theory errors remain smaller than the uncertainties in $^4$He observations, even with the dispersion in recent neutron lifetime measurements. For the other light-element predictions, $\tau_n$ contributes negligibly to their error budget. Turning the problem around, we combine present BBN and cosmic microwave background (CMB) determinations of the cosmic baryon density to *predict* a “cosmologically preferred” mean life of $\tau_n(BBN + CMB) = 870 ± 16 \text{ sec}$, which is consistent with experimental mean life determinations. We go on to show that if future astronomical and cosmological helium observations can reach an uncertainty of $\sigma_{\text{obs }}(Y_p)$ = 0.001 in the $^4$He mass fraction $Y_p$, this could begin to discriminate between the mean life determinations.

Next-Generation Simulations of The Remarkable Deaths of Massive Stars (Junior Workshop (May 21 - 22))

• Carl E. Fields (LANL)

Multidimensional progenitor models can enable us to capture the chaotic nuclear shell burning occurring deep within the interior of a massive star. I will discuss ongoing efforts to progress our understanding of the nature of massive stars through next-generation hydrodynamic stellar models. In particular, I will present recent results of a three-dimensional hydrodynamic massive star model including rotation evolved for the final 10 minutes before collapse. These recent results suggest that realistic 3D progenitor models can be favorable for obtaining robust models of CCSN explosions and affect the properties of the compact objects they form. I will conclude with a brief discussion of the implications our models have for predictions of multi-messenger signals from CCSNe.

Core-Collapse Supernovae: the role of the Si/O interface and the connection between explosion and progenitor structure

• Luca Boccioli (University of Notre Dame)

The explosion mechanism of core-collapse supernovae has been a longstanding problem in nuclear astrophysics. In the last decade, important steps towards a thorough understanding of what causes supernovae to explode have been made, thanks to the development of very detailed three-dimensional simulations. However, a lot of work still needs to be done. In this talk, I will focus on the connection between the thermodynamic and compositional structure of the progenitor star and its subsequent explosion. I will use spherically symmetric simulations (where neutrino-driven convection is included via a mixing length approach) to simulate the collapse and shock revival of stars with different initial masses. I will highlight how discontinuities in the density profile at the onset of collapse can be used to predict the outcome of the explosion. Specifically, I will highlight the importance of neutrino-driven convection in triggering the explosion when these discontinuities are accreted through the shock. I will then briefly compare these results to the previous criterion by Ertl et al. (2016). Finally, I will comment on the differences between stellar evolution codes and reaction rates and how they can significantly change the explodability pattern of supernovae.

Proto-Neutron Star Convection, the Neutrino-Driven Wind, and the r-Process

• Brian Nevins (Michigan State University)

The neutrino-driven wind has been proposed and investigated as a site for r-process nucleosynthesis several times since the first promising simulations were presented in 1994. Since then, simulations have shown that a wind heated only by neutrinos cannot produce a strong r-process. However, several groups have noted that introducing a secondary heating source within the wind can change the conditions sufficiently for an r-process to take place. One possible source for this secondary heating is gravito-acoustic waves, generated by convection in the proto-neutron star, which shock and deposit energy into the wind. We present a systematic investigation of the impact of these convection-generated waves within the wind on potential nucleosynthesis, finding that they allow strong r-processing in broad regions of the parameter space.

Extraction of Gamow-Teller Strength Using (d,2He) Reaction in Inverse Kinematics

• Zarif Rahman

Electron-capture (EC) rates play a decisive role in core-collapse and thermonuclear supernovae, the crust of accreting neutron stars in binary systems, and the final core evolution of intermediate mass stars. Charge-exchange reactions (CERs) at intermediate energies (~100 MeV) are crucial in extracting information for neutron-rich nuclei as the EC Q-values are positive for such nuclei. The differential cross-sections in CERs at zero momentum transfer are proportional to the Gamow-Teller strength, B(GT), from which the EC rates can be calculated. In a first of a kind experiment, the S800 spectrometer at National Superconducting Cyclotron Laboratory (NSCL) along with Active-Target Time Projection Chamber (AT-TPC) setup was used to run an experiment with ($d$,$^{2}$He) probe in inverse kinematics to study unstable nuclei. Data from the experiment for the $^{13}$N($d$,$^{2}$He)$^{13}$C reaction is being analyzed to extract the differential cross-section for ground and excited states which will be utilized in measuring the B(GT).

Proton ingestion flashes in Type I X-ray bursts

• Simon Guichandut (McGill University)

Type I X-ray bursts are a result of the runaway nuclear burning that takes place in the atmospheres of accreting neutron stars. In cases where the accumulating fuel is hydrogen-rich, some bursts may ignite in a pure helium layer after the depletion of hydrogen through burning in the hot CNO cycle. Within seconds, the convection zone generated by helium burning collides with the overlying hydrogen shell, injecting fresh protons into the burning mixture. This process triggers further burning and expansion of the convection zone. I will present new simulations of this type of burst with the *MESA* code, and show that the shape of the light curve is directly influenced by the effect of convection at the onset of the burst, potentially enabling a new way to probe neutron star surface physics. However, multidimensional fluid simulations are required to accurately model the intricate interaction between explosive nuclear burning and convection. To that end, I will discuss our ongoing efforts to model these bursts in low-Mach number hydrodynamics using the *MAESTROeX* code.

Modeling astrophysical events with nuclear reaction network (Junior Workshop (May 21 - 22))

• Irin Sultana (Central Michigan University)

Nuclear astrophysics seeks to understand the processes that led to the origin of elements. A nuclear reaction network model describes the evolution of the abundance of elements as a function of time during various stellar nucleosynthesis and explosive events. Accreting neutron stars provides one of the few avenues to study matters in extreme temperature and density conditions. In this talk, I will focus on surface explosions on accreting neutron stars and how different nuclear reactions that power the cataclysmic event play a key role in model-observation comparison. I will discuss the effect of the uncertainties in the nuclear reactions using single-zone and multizone models for a set of different compositions of the material accreted from the companion star. I will also connect other observables from accreting neutron stars with different model calculations. Finally, I will provide an outlook on how sensitivity studies can help prioritize future experimental and observational efforts.

First cross-section measurement of the weak r-process 88Sr(⍺,n)91Zr reaction

• Chloé Fougères (Argonne National Laboratory)

Half of the elements heavier than iron is produced by the r-process consisting of rapid neutron-capture reactions on neutron-rich nuclei. The other half mostly originates from the s-process. Although proven to occur during neutron-star mergers, other sites of the r-process and other mechanisms are still under consideration to explain abundance patterns above Fe. For instance, a subset of low metallicity stars presents abundances at the first peak possibly explained by a truncated weak r-process which could be active in neutron-star mergers and 𝜈-winds after core-collapse supernovae (CCSNe). In the latter, the synthesis of elements around Z~40 in the expelled matter is mainly driven by (⍺,n) and (n,𝛾) reactions at temperatures of 2 - 5 GK. To date, ⍺-induced reactions have been poorly measured and rates are calculated with statistical Hauser-Feshbach models where nuclear physics inputs like the ⍺-Optical-Model Potential (⍺-OMP) choice lead to uncertainties of several orders of magnitude. These nuclear uncertainties are too important to gain insights on the CCSNe 𝜈-wind conditions while comparing models to observed abundances in metal-poor stars ([1, 2]). Hence the need for experimental work on (⍺,xn) reactions affecting the weak r-process in CCSNe 𝜈-winds and nuclear reaction theory. An experiment was performed at the Argonne Tandem Linac Accelerator System facility to measure the weak r-process 88Sr(⍺,n)91Zr cross sections at astrophysics energies for the first time, and results will be given. Such an experiment, based on the active gaseous target technique in inverse kinematics with the ionisation chamber MUSIC [3], has already been successful ([4, 5]). The 4.6 MeV/u 88Sr beam traveled through the 4He gas volume at 500 Torr. The detector has an electrically-segmented anode allowing to measure the excitation function at different energies while the incident beam slows down in the gas. Reaction events were identified using sharp variations in energy loss due to the Z+2 change between the beam and the recoil. Digital data acquisition electronics were employed for the first time. Measured cross sections were compared to statistical Hauser-Feshbach calculations with Talys and a set of ⍺-OMP, constraining the latter. The 88Sr(⍺,n)91Zr thermonuclear reaction rate was determined. Future experimental efforts will finally be discussed. **References** [1] J. Bliss *et al.*, PRC **101** (2020). [2] A. Psaltis *et al.*, ApJ **935** (2022). [3] P.F.F. Carnelli *et al.*, NIMA **199** (2015). [4] M. L. Avila *et al.*, PRC **94** (2016). [5] W.-J. Ong *et al.*, PRC **105** (2022).

The Abundance Patterns of (now) Disrupted Dwarf Galaxies

• Guilherme Limberg (Universidade de São Paulo and University of Chicago)

In the context of hierarchical assembly of galaxies in a Λ cold dark matter cosmology, the stellar halos of massive, Milky Way-like, systems are expected to be entirely comprised of debris from tidally-disrupted dwarf galaxies. Therefore, in principle, it should be possible to isolate which stars in the Milky Way’s halo were accreted and, hence, reconstruct the chemical-evolution of their original parent low-mass galaxies, providing a glimpse into their early formation and evolution at high redshift using observations of nearby stars. Since the advent of the Gaia mission, in particular its second data release in 2018, the availability of astrometric information for more than a billion stars has allowed us to disentangle this fine-grained structure of the Galactic halo from stellar kinematics/dynamics. Here, I will discuss what can be learned from the elemental-abundance patterns of these ancient now-destroyed dwarf galaxies. Because their stars are much closer, hence brighter, than surviving present-day satellites of the Milky Way, this approach constitutes an alternative to investigate the early formation history of these small galaxies. I will go through several results using public spectroscopic catalogs for the so-called Helmi streams, Gaia Sausage/Enceladus, and Sagittarius stream, which are all halo substructures of dwarf-galaxy origin. For example, (*i*) we found that high-metallicity stars in the Helmi streams have low α-element abundances in comparison to the overall halo, (*ii*) the Gaia Sausage/Enceladus experienced higher star-formation efficiency at early times in comparison to the similar-sized Magellanic Clouds, and (*iii*) the Sagittarius stream contains a population of carbon-enhanced metal-poor stars in conformity with the Milky Way itself. I will also present preliminary results on the Wukong stellar stream, also known as “LMS-1”, using high-resolution spectroscopy obtained with the MIKE spectrograph on the Magellan telescope (6.5m). Although these chemical-abundance studies of disrupted dwarf galaxies are still incipient, they present the opportunity to bridge the gap between low- and high-redshift observations.

The Bare Minimum (Mass) for Multiple Populations

• Sam Usman (UChicago)

The stellar stream 300S is a remnant of a globular cluster accreted onto the Milky Way from an in-falling galaxy. Like intact Milky Way globular clusters of a comparable mass (~$10^5$ M$_☉$), we expected about half of 300S’s stars to be enriched in a phenomenon called multiple populations. We studied the elemental abundances of eight red giant branch stars found in 300S using high-resolution spectroscopy from the MIKE/Magellan telescope. We identified just one star that has the signature light-element enrichment of a second-population star. We suggest 300S straddles the initial mass threshold for the creation of multiple populations, but experiences none of the mass loss to the galactic disk that Milky Way clusters endure over their lifetimes. 300S is therefore a significant benchmark for constraining the minimum initial mass for the creation of multiple populations.

Metallicity Distribution Function of the Ultra-Faint Dwarf Galaxy Reticulum II

• Alice Burington (University of Chicago)

The metallicity distribution function of stars in ultra-faint dwarf galaxies (UFDs) provides insight into their formation histories. Currently, metallicities are only measured using red-giant branch (RGB) stars in UFDs, greatly limiting the number of stellar metallicities that are possible to measure. Reticulum II is a UFD that currently has only 16 RGB stars with known metallicities. We present Magellan/IMACS spectroscopy of main sequence turn-off stars in Reticulum II, increasing the number of stellar metallicities by ~6 times. This is currently the most populated metallicity distribution for any UFD. We fit analytic models of metallicity distributions to this data, which constrains the star formation history of this ancient relic galaxy during the epoch of reionization.

Computational Nuclear Astrophysics (Main Conference (May 23 - 26))

• Falk Herwig (University of Victoria)

I this talk I discuss different approaches to construct computer simulations of the origin of the elements in stars and stellar explosions. Computational nuclear astrophysics is a classical multi-physics, multi-scale problem in which different physics operators, such as nuclear physics, fluid dynamics due to various macroscopic processes and thermal transport are interacting and operating on vastly different spatial and time scales. Key in realistic computational nuclear astrophysics modeling is to make simplifying assumptions that balance the often-orthogonal requirements imposed by the interaction of these different time scales. I will demonstrate and discuss these general principles in the context of simulations of convective-reactive nucleosynthesis in which macroscopic mixing time scales and nuclear reaction time scales are of similar magnitude and thus these two processes are inseparably intertwined. Examples include the intermediate neutron-capture process as well as nuclear shell-interactions in the late phases of massive stars, among others.

The Photometric Revolution – Stellar Parameters and Elemental Abundances for over 50 Million Stars … and Counting

• Timothy Beers (University of Notre Dame)

Galactic Archaeologists are opening a revolutionary era for the determination of stellar parameters, such as effective temperature, surface gravity, metallicity, and ages, for a substantial fraction of the stars in the Milky Way, and eventually in dwarf galaxies and other nearby galaxies of the Local Group. The most recent surveys implement a combination of narrow- and intermediate-band filters that further enable measurements of a subset of the most important elements for probing stellar populations, in addition to [Fe/H], such as [C/Fe], [N/Fe], [Mg/Fe], and [Ca/Fe]. The recently (or nearly) completed surveys, including the SkyMapper Southern Survey (SMSS) and The Stellar Abundances for Galactic Exploration Survey (SAGES) in the North, have already contributed over 50 million stars with estimates of [Fe/H]. The ongoing Javalambre Photometric Local Universe Survey (J-PLUS) and the Southern Local Universe Survey (S-PLUS) will contribute another 25 million stars with additional elemental abundances over the next two years. For those who hunger for the most chemically primitive stars, we have already identified over 1 million Very Metal-Poor stars with [Fe/H] < -2.0, and over 50,000 Extremely Metal-Poor stars with [Fe/H] < -3.0. Extension of these techniques to other large-scale surveys in the future will also be discussed.

Transuranic fission fragments in stars

• Ian Roederer (University of Michigan)

I present evidence supporting the detection of fission fragments of transuranic elements among the abundance patterns of r-process-enhanced stars. A meta-analysis of 42 r-process-enhanced stars reveals that the elements Ru, Rh, Pd, and Ag (atomic numbers 44 $\leq$ Z $\leq$ 47, mass numbers 99 $\leq$ A $\leq$ 110) exhibit a correlation with abundances of heavier elements (63 $\leq$ Z $\leq$ 78, A > 150) that is not shared by their immediate neighbors (34 $\leq$ Z $\leq$ 42 and 48 $\leq$ Z $\leq$ 62). Coproduction via fission fragments of transuranic nuclei provides the most compelling explanation for this behavior. These signatures suggest that neutron-rich fissioning nuclei with A > 260 are produced in r-process events. I also discuss prospects for detecting transuranic nuclei in multi-messenger observations of merging pairs of neutron stars and the kilonova events that accompany them. This work is supported by NSF grants PHY 14-30152 (JINA-CEE), AST 1815403/1815767, and AST 2205847. This work is also supported by NASA/STScI/HST grants GO-15657 and GO-15951.

Impact of nuclear uncertainties in the r-process nucleosynthesis of heavy elements (Main Conference (May 23 - 26))

• Samuel A. Giuliani (Universidad Autónoma de Madrid)

The rapid neutron capture process, or r process, is responsible for the production of about half of the elements heavier than iron found in nature, including the heaviest uranium and thorium [1, 2]. During the r process, several thousands of neutron-rich nuclei are synthesized in few seconds, powering an electromagnetic transient known as kilonova. Since most of such exotic nuclei have never been experimentally observed due to their exceedingly short half-lives, the estimation of abundances and kilonova light curves must rely upon the theoretical predictions of nuclear properties [3, 4]. During this talk, I will present calculations of nuclear properties and stellar reaction rates obtained within the energy density functional (EDF) framework. Several EDF parametrizations have been employed in order to asses the impact of systematic uncertainties in the r process nucleosynthesis. In particular, I will focus on the nucleosynthesis of translead elements in the merger of two neutron stars, and the role that nuclear masses, beta decays and fission play in shaping the r-process abundances and kilonova light curves. 1.E. M. Burbidge, G. R. Burbidge, W. A. Fowler, and F. Hoyle, Rev. Mod. Phys. 29, 547 (1957). 2. A. G. W. Cameron, Publ. Astron. Soc. Pacific 69, 201 (1957). 3. C. J. Horowitz, et al., J. Phys. G Nucl. Part. Phys. 46, 083001 (2019). 4. J. J. Cowan, et al., Rev. Mod. Phys. 93, 015002 (2021).

Role of neutron-rich nuclei in r-process nucleosynthesis (Main Conference (May 23 - 26))

• S. Nishimura (RIKEN)

Where and how were heavy elements which contain many neutrons relative to proton, synthesized? With regards to the origin of these heavy elements, a reaction in which nuclei capture neutrons in a fast and continuous manner during the explosion of a star was proposed and named the rapid neutron capture process (r process) [1]. In 2017, a binary neutron star merger event was discovered by simultaneous observations of gravitational and electromagnetic waves, and its kilonova was also identified, suggesting the synthesis of heavy elements. Were heavy elements such as gold, platinum, and even uranium synthesized in binary neutron star mergers, supernova explosions, or collapsars [2-4]? Analysis of the unique heavy-element compositions left behind in the solar system, meteorites, and old metal-poor stars has begun. The key to deciphering the traces left behind by isotopic elements lies in the thousands of neutron-rich nuclei that disappeared in an instant. Here, we introduce the experimental research on the explosive r-process nucleosynthesis and future perspective at RIBF [5]. [1] E.M. Burbidge, G.R. Burbidge, W.A. Fowler, and F. Hoyle, Rev. Mod. Phys. 29, 547 (1957). [2] S. Wanajo et al., Astrophys. Jour. Lett. 789: L39 (2014). [3] C. Kobayashi, A.I. Karakas, and M. Lugaro, Astrophys. Jour. 900, 179 (2020). [4] J. Barnes and B.D. Metzger, Astrophys. Jour. Lett. 939: L29 (2022). [5] V.H. Phong et al., Phys. Rev. Lett. 129, 172701 (2022).

Quantified Nuclear Mass Model for Nuclear Astrophysics Simulations

• Rahul Jain

Nuclear mass is a fundamental property of the atomic nucleus. Nuclear binding energies determine the boundaries of the nuclear landscape, the particle driplines, as well as the Q-values of nuclear reactions. As a result, they are key inputs for astrophysical models and simulations. We are, however, limited in our ability to experimentally measure the masses of all particle-bound nuclei and have to often rely on theoretical predictions. Since current global nuclear models are fitted to known experimental data and then used to predict masses over the whole nuclear chart, assessing their uncertainties in regions far from stability is a non-trivial task. This makes it difficult to quantify the impact of the uncertainties of nuclear masses in astrophysical simulations involving exotic nuclei. Moreover, different theoretical models vary in their predictions of nuclear masses leaving us indecisive on which model to choose for a particular application. To overcome these limitations, we present a data-driven mass extrapolation technique where binding energy residuals are modeled using a fully Bayesian Gaussian Process Regression. The statistically corrected predictions obtained from 11 different nuclear mass tables are then combined via Bayesian model averaging, according to their experimental evidence. This leads us to a quantified mass model providing uncertainties and covariances that can be used for astrophysical modeling and sensitivity studies. We further show that any derived quantities like the separation energies, Q-values, etc. also have quantified uncertainties which depend on the covariances of predicted masses. Such correlations between mass predictions are utmost necessary for honest uncertainty quantification of any derived quantity. The resulting tables of masses and covariances can be directly used in astrophysical simulations.

Future Mass measurements for the r-process using Canadian Penning Trap at the N=126 Factory

• Biying Liu

The rapid neutron capture process (r-process) is responsible for the production of almost half of the natural elements heavier than iron. Precise and accurate masses of neutron-rich isotopes are needed for reliable r-process abundance calculations for the models of neutron star merger and other potential astrophysical sites. The Canadian Penning Trap (CPT) has been at the Argonne National Laboratory's CARIBU facility for over a decade, where it measured the masses of over 300 nuclei produced from the spontaneous fission of CARIBU’s ${}^{252}$Cf source with a typical precision of around 10 keV. In particular, over the past few years, masses of interest in forming the rare-earth peak in the r-process abundance pattern were measured using the CPT [1,2]. Upon reaching the yield limit of CARIBU, the CPT is now moving to the future $N=126$ Factory, which uses multi-nucleon transfer reactions to produce neutron-rich nuclei. These include rare-earth isotopes such as Nd and Sm that will help better constrain the r-process astrophysical condition for the formation of the rare-earth peak [2]. Furthermore, the $N=126$ Factory enables to access the $N=126$ closed shell for the first time, where mass measurements in this region allow the investigation of the persistence of $N=126$ shell closure and the study of the formation of the last r-process abundance peak left. The status of the $N=126$ Factory and CPT, as well as future measurements at the $N=126$ Factory will be presented. This work is supported in part by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357; by NSERC (Canada), Application No. SAPPJ-2018-00028; by the National Science Foundation under Grant No. PHY-2011890; by the University of Notre Dame; and with resources of ANL’s ATLAS facility, an Office of Science User Facility. [1] R. Orford et al., Precision mass measurements of neutron-rich neodymium and samarium isotopes and their role in understanding rare-earth peak formation, Phys. Rev. Lett. 120, 262702 (2018). [2] R. Orford et al., Searching for the origin of the rare-earth peak with precision mass measurements across Ce-Eu isotopic chains, Phys. Rev. C, 105, L052802 (2022).

Precision mass measurements for the rapid neutron capture process

• Anu Kankainen (University of Jyväskylä)

Nuclear masses are key inputs for the astrophysical rapid neutron capture process, the r process. Today, the most precise mass measurements are performed using the Penning-trap mass spectrometry, with which precisions of 10 ppb or better are typically achieved. In this contribution, I will present recent results on precision mass measurements of neutron-rich nuclides performed with the JYFLTRAP double Penning trap [1], located at the Ion Guide Isotope Separator On-Line (IGISOL) [2] facility at the University of Jyväskylä, Finland. We have recently commissioned the phase-imaging ion cyclotron resonance (PI-ICR) technique at JYFLTRAP [3,4]. The method provides a much higher resolving power than the conventionally used time-of-flight ion cyclotron resonance technique. With the PI-ICR technique, even low-lying (E<100 keV) isomeric states can be resolved from the ground states and both states measured separately. Isomers can play a significant role in the r process and such “astromers” can affect kilonova light curves [5]. Many isomeric states are purely beta-decaying and their excitation energy has remained unknown before the PI-ICR technique. Altogether we have measured around 40 isomeric states with JYFLTRAP during recent years. As an example, I will show how precision measurements of neutron-rich Rh ground- and isomeric-state masses [6] reveal changes to the adopted mass values and affect the related neutron-capture reaction rates. **References** [1] T. Eronen et al., Eur. Phys. J A 48 (2012) 46. [2] I.D. Moore et al., Nucl. Instr. Meth. Phys. Res. 317 (2013) 208. [3] D.A Nesterenko et al., Eur. Phys. J. A 54 (2018) 154. [4] D.A Nesterenko et al., Eur. Phys. J. A 57 (2021) 302. [5] G. Wendell Misch et al., Astrophys. J. Lett. 913 (2021) L2. [6] M. Hukkanen et al., Phys. Rev. C 107 (2023) 014306.

Time-of-Flight Magnetic-Rigidity (TOF-Bρ) Mass Measurements at NSCL and FRIB

• Irin Sultana (Central Michigan University)

The time-of-flight (TOF) magnetic-rigidity (B$\rho$) technique offers access to short-lived exotic nuclei. The TOF-B$\rho$ method has been implemented at the National Superconducting Cyclotron Laboratory (NSCL) to measure masses that are relevant for understanding the processes occurring in the crust of accreting neutron stars and the evolution of nuclear shell closures towards the neutron drip-line, which are valuable input for r-process models. In the last TOF-B$\rho$ experiment at NSCL, we aim to measure the masses near the $\rm ^{42}{Si}$ region using the fragmentation of $\rm ^{48}{Ca}$. A previous TOF-B$\rho$ experiment at NSCL measured the masses near the N=70 region from Zr to Ru using the fragmentation of $\rm ^{124}{Sn}$. I will present the status and results of these experiments. With the Facility for Rare Isotope Beams (FRIB) in operation, we can expand the current reach of the nuclear mass surface. I will briefly discuss the future plans of TOF-B$\rho$ collaborations at FRIB. This work is supported by U.S. DOE grant DE-SC0020406, DE-FG02-88ER40387, DE-SC0019042, DE-NA0003180, DE-NA0000979, and DE- FG02-94ER40848 and by NSF grant PHY-1430152, PHY-1712832, PHY-1565546, and PHY-1714153.

Gravitational-Wave Observations and Nuclear Astrophysics (Main Conference (May 23 - 26))

• Jocelyn Read (CSU)

Gravitational-wave observatories have established a new field of transient astronomy. The most recent LIGO-Virgo-Kagra catalog, GWTC-3, identifies 90 merging binaries, which range from a double neutron star with a total mass of 2.7 M⨀ at 40 Mpc (GW170817) to a double black hole with a total mass of 150 M⨀ at 5.3 Gpc (GW190521). These observations have many potential implications for nuclear science: revealing the remnants of stellar evolution and explosions in merging binary systems, constraining rates and astrophysical environments of heavy-element nucleosynthesis events, and illuminating the dense matter dynamics of the mergers of neutron stars. I will describe some of key results from existing observations, some prospects for the new Advanced LIGO and Virgo run starting at the end of May, and the science potential of proposed next-generation observatories like Cosmic Explorer.

The Nuclear Equation of State from Experiments and Astronomical Observations

• Rohit Kumar (FRIB, MSU, Michigan )

With recent advances in astronomical observations, major progress has been made in determining the pressure of neutron star matter at high density. This pressure is constrained by the neutron star deformability, determined from gravitational waves emitted in a neutron-star merger, and the mass-radius relation of two neutron stars, determined from a new X-ray observatory on the International Space Station. Previous studies have relied on nuclear theory calculations to constrain the equation of state at low density. In this work, we combined constraints composed of three astronomical observations and twelve nuclear experimental constraints that extend over a wide range of densities to obtain the nuclear equation of state. This data-centric result obtained using the Bayesian framework provides benchmarks for theoretical calculations and modeling of nuclear matter and neutron stars. Furthermore, it provides insights into the microscopic degrees of freedom of the nuclear matter equation of state and on the composition of neutron stars and their cooling via neutrino radiation.

Production of Blue Kilonovae from Hypermassive Neutron Star Remnants

• Sanjana Curtis (University of Chicago)

When binary neutron stars merge together, they eject neutron-rich matter that undergoes r-process nucleosynthesis, synthesizing some of the heaviest elements in our Universe and powering an electromagnetic transient called a kilonova. With the detection of the kilonova associated with the GW170817 event, we have obtained strong evidence that such mergers are a heavy element production site. However, almost five years after this remarkable detection, the origin of the blue component of the observed kilonova (AT2017gfo) remains a mystery. In this talk, I will present a 3D general-relativistic magnetohydrodynamic simulation of a hypermassive neutron star remnant formed in the aftermath of a binary neutron star merger. The simulation uses a newly implemented M1 neutrino transport scheme to track neutrino-matter interactions and is thus uniquely poised to predict the resulting nucleosynthesis and kilonova emission. I will show that outflows from such remnants are an important component of merger ejecta and can produce a blue kilonova consistent with AT2017gfo. I will also discuss the diversity of kilonova transients expected from merger events and how we can better prepare for their detection.

Searching for counterparts of explosive transients with the GOTO network

• Duncan Galloway (Monash University)

The impetus for wide-field searches for counterparts of explosive transients including binary neutron-star mergers, supernovae, and tidal disruption events has never been higher. The imminent resumption of operations with the LIGO-Virgo-Kagra network of gravitational wave detectors offers particular challenges for optical observers, primarily due to the poor (~100 deg$^2$) localisation regions. I will describe a new facility, the Gravitational-wave Optical Transient Observer (GOTO; http://goto-observatory.org) network, featuring instruments in the Canary Islands and south-east Australia, designed to overcome these challenges. A modular design featuring eight 40-cm telescopes on each mount provides a composite field of view of around 40 square degrees per instrument, capable of quickly and autonomously covering large fields of view in response to observing triggers. I will report on the status and progress of the network and our expectations for the detection of future transients.

Separation of Neutron Rich Nuclides in White Dwarfs

• Matt Caplan (Illinois State University)

The mixtures of elements inside white dwarf stars separate upon crystallization, enhancing (or depleting) the concentration of neutron rich nuclides like $^{22}$Ne and $^{56}$Fe in the solid or liquid phases. This talk will describe recent work using analytic phase diagrams and molecular dynamics simulations to study how plasma mixtures in white dwarfs separate and determine the effects of separation on observable astrophysics. Processes such as precipitation and distillation may result in crystalline $^{22}$Ne or $^{56}$Fe inner cores (or shells) in C-O white dwarfs and $^{56}$Fe cores (or shells) in O-Ne white dwarfs. While the impact of separation on white dwarf cooling is relatively straightforward to calculate, the effects of these substructures on nuclear burning when white dwarfs explode in type 1a supernova are less well understood. By enhancing the concentration of neutron rich nuclides in the center of the star these substructures may play a role in the production of nuclides such as $^{55}$Mn and $^{58}$Ni and may be of interest to future work.

Heavy Element Nucleosynthesis from the Births of Black Holes (Main Conference (May 23 - 26))

• Brian Metzger

The origin of the heaviest elements in our universe, particularly those produced via the rapid neutron capture process ("r-process"), remains a question of intense debate. Although the kilonova emission that accompanied GW170817 revealed neutron star mergers to be an important r-process source, several independent observations hint that mergers may not be the only source, particularly early in the history of our Galaxy and Universe. Outflows from the accretion disk feeding the newly-formed black hole - that responsible for powering the gamma-ray burst (GRB) jet - was likely the dominant source of r-process elements in GW170817. Broadly similar accretion flows are created in another explosive transient - the collapse of massive rotating stars ("collapsars") which give rise to GRBs of longer duration, and simple estimates show that the integrated r-process yields of collapsars could compete with those of neutron star mergers over the history of the Galaxy. I will discuss observational tests of whether collapsars produce r-process elements using infrared observations of GRB supernovae, such as with JWST and Roman Space Observatory.

Observational signature of magneto-rotaional supernovae associated with r-process nucleosynthesis

• Nobuya Nishimura (RIKEN)

Magnetorotational-driven supernovae (MRNSe) are a peculiar type of core-collapse SNe. Their progenitors are fast-rotating massive stars with strong magnetic fields, making them candidates for the central engine of hypernovae and gamma-ray bursts. They are also expected to be astronomical sites for the r-process, as they have a different explosion mechanism from regular SNe. MRSNe may have very neutron-rich ejecta suitable for the r-process due to the strong effect of the jet-driven explosion. In studies of galactic chemical evolution, MRSNe are expected to be additional r-process sources because they have different frequencies and delay times from neutron-star mergers. Although some observations suggest jet-like SNe, the occurrence of r-process nucleosynthesis has never been directly confirmed.In this presentation, we focus on the effect of r-process nucleosynthesis in MRSNe on possible observational properties in SN light curves. The r-process occurring in the central region of the SN provides different opacity and heating sources compared to canonical core-collapse SNe. We quantitatively investigate the effects of r-process elements and ${}^{56}$Ni abundances on the light curves based on a series of radiative hydrodynamics simulations. We confirm that the influence of the r-process is not significant for all models, which is consistent with the fact that r-process elements have not yet been identified in SNe observations. However, we have found some models where the existence of r-process elements can be observationally confirmed by current high-precision observations, such as those made by JWST, as well as future telescopes.

Timing the r-process Enrichment of the Ultra-faint Dwarf Galaxy Reticulum II

• Alexander Ji (University of Chicago)

Identifying the dominant astrophysical source of elements synthesized in the rapid neutron capture process (r-process) is an open question in nuclear astrophysics. One way to distinguish between different astrophysical sources of r-process elements is measuring their delay times, i.e. the time it takes to synthesize r-process elements after a burst of star formation. The ultra-faint dwarf galaxy Reticulum II exhibits a unique chemical evolution history, with ~70% of its stars strongly enhanced in r-process elements due to a single r-process enrichment event. This provides a rare opportunity to put limits on the delay time of r-process nucleosynthesis in the early universe. Using new star formation histories derived from deep Hubble Space Telescope photometry, we show that ~30% of stars in this galaxy formed within 500 ± 200 Myr of the onset of star formation. The combination of the star formation history and the prevalence of r-process-enhanced stars demonstrates that the r-process elements in Ret II must have been synthesized early in its initial star-forming phase. We therefore constrain the delay time between the formation of the first stars in Ret II and the r-process nucleosynthesis to be less than 500 Myr. This measurement rules out an r-process source with a delay time of several Gyr or more, such as GW170817.

Uranium Abundances and Ages of r-process Enhanced Stars with Novel U II Lines

• Shivani Shah (University of Florida)

The ages of the oldest stars shed light on the birth, chemical enrichment, and chemical evolution of the universe. Nucleocosmochronometry (radioactive-decay dating) provides an avenue to determining the ages of these stars independent from stellar evolution models. The uranium abundance, which can be determined for metal-poor *r*-process enhanced (RPE) stars, has been known to constitute one of the most robust chronometers known. So far, U abundance determination has used a *single* U II line at λ3859 Å. Consequently, U abundance has been reliably determined for only five RPE stars. In this talk, I will present results from the first homogeneous U abundance analysis of four RPE stars using two novel U II lines at λ4050 Å and λ4090 Å, in addition to the canonical λ3859 line. I will discuss the reliability of the two new U II lines and present revised U abundances for these stars. I will also discuss the technique of nucleocosmochronometry and present stellar age estimates of these old metal-poor stars. Furthermore, I will discuss the major factors contributing to the uncertainties in the U abundances and the stellar ages as well as the prospects of addressing these uncertainties in the future. Finally, I will discuss the potential impact of these results in robustly determining U abundances and nucleocosmochronometric ages for a larger sample of RPE stars, with the overarching goal of constraining chemical enrichment and evolution in the early universe, especially of *r*-process elements.

Nuclear Astrophysics Experiments with Storage Rings (Main Conference (May 23 - 26))

• Rene Reifarth (Goethe University Frankfurt (DE))

Most of the time, stars gain their energy from fusion of the very light left-overs of the Big Bang into heavier elements over long periods of time. The observation of radioactive isotopes in different regions of the Universe is an indicator of this ongoing nucleosynthesis. In addition, short-lived nuclei are often intermediate steps during the nucleosynthesis in stars. A quantitative analysis of these relations requires a precise knowledge of reaction cross sections involving unstable nuclei. The corresponding measurements are very demanding and the applied techniques therefore manifold. Ion storage rings offer unprecedented possibilities to investigate radioactive isotopes of astrophysical importance in inverse kinematics. During the last years, a series of pioneering experiments proofed the feasibility of this concept at the Experimental Storage Ring (ESR) at GSI. I will present recent experiments and ideas for future setups for the investigation of capture reactions with astrophysical motivation.

12C – A Node in the Chemical Evolution of the Universe (Main Conference (May 23 - 26))

• Michael Wiescher (University of Notre Dame)

The production and depletion of 12C is a fundamentally important question in our understanding of the chemical evolution of the universe. 12C is produced in large abundances in first stars through the cluster configurations of light isotopes. It is depleted by the 12C(α,γ)16O reaction, a reaction that determines the composition of white dwarfs as the final stage of low mass stars. It sets the conditions for pair-production supernova which completely annihilate the most massive stars in our universe as reflected in the black holes gap. As integral part of the CNO cycles, the 12C(p,γ) reaction feeds 13N whose decay is an important neutrino source from our sun and the 12C+12C fusion triggers thermonuclear supernovae (Type Ia) and type I superbursts. Last not least 12C is not only a node in the chemical evolution of the universe, but also in the biological evolution since it is the key for the multitudes of biochemical reactions that led to the origin of life as we know. This talk will provide an overview of the nuclear reaction rates involving 12C at all these sites, the associated uncertainties and the observational signatures.

Nucleosynthesis based on modern core-collapse supernova simulations

• Andre Sieverding (Max-Planck Institute for Astrophysics)

Core-collapse supernovae have long been understood as a major contributor to cosmic nucleosynthesis. Most of the current understand is, however, based on parameterized models. "Ab-initio", parameter-free, core-collapse supernova simulation in 2D and 3D are now becoming more mature and provide new insights into the nucleosynthesis conditions in supernovae. In general, mutli-D supernova simulations provide a wider range of conditions that may allow to solve the underproduction found for some elements in canonical 1D calculations, such as Sc and Zn. I will present recent nucleosynthesis results based on modern simulations and highlight some of the challenges in obtaining reliable nucleosynthesis results from large-scale simulations.

First direct measurement of the 65 keV resonance in the 17O(p,g)18F reaction at LUNA

• Giovanni Francesco Ciani (University degli Studi di Bari & INFN Ba)

The 17O(p,g)18F reaction plays a key role in the hydrogen burning in CNO cycle At temperatures of interest for the H shell burning in AGB stars, the reaction rate is dominated by the Ecm = 65 keV resonance. The strength of this resonance is presently determined only through indirect measurements, with a literature value wg = (16 ± 3) neV[1], leading to an expected counting rate of N = 0.3 reactions/C for typical experimental quantities . Recently, the LUNA collaboration has performed a new measurement of the 17O(p,g)18F cross section in the low-background environment of the deep underground Laboratori Nazionali del Gran Sasso (LNGS, Italy). This unique location, combined with the high stable intense proton beam (< I >= 200 μA) of the LUNA accelerator, an improved setup based on a segmented 4pi BGO detector with proper shielding for high sensitivity measurements and a devoted technique for the suppression of the beam induced background[2], allowed to directly measure for the first time the 65 keV resonance strength Moreover, from this strength a new value of the proton width was evaluated which seems to confirm what measured in a previous 17O(p,a)14N measurement at LUNA[3], larger than the literature values[4]. In the talk the experimental techniques and the preliminary results of the LUNA collaboration will be presented. [1] Fox C. et al,PHYSICAL REVIEW C 71, 055801 (2005) [2] Skowronski J. et al, Accepted on J. Phys. G. [3] Bruno C.G. et al., PRL 117, 142502 (2016) [4] Buckner M.Q. et al., PHYSICAL REVIEW C 91, 015812 (2015)

Galactic chemical Evolution with short lived radioactive isotopes

• Benjamin Wehmeyer (Konkoly Obs & Univ of Hertfordshire)

Studying the galactic chemical evolution with short lived radioisotopes (SLRs) has a significant advantage over using stable elements: Due to their radioactive decay, SLRs carry additional timing information on astrophysical nucleosynthesis sites. We can use meteoritic abundance data in conjunction with a chemical evolution model to constrain the physical conditions in the last rapid neutron capture process event that polluted the early Solar system prior to its formation [1]. Further, with the help of detections of live SLRs of cosmic origin in the deep sea crust [2], we can use these data in a 3-dimensional chemical evolution code to explain why different classes of radioisotopes should often arrive conjointly on Earth, even if they were produced in different sites (e.g., neutron star mergers, core-collapse/thermonuclear supernovae) [3]. Finally, we included radioisotope production into a cosmological zoom-in simulation to create a map of Al-26 decay gamma-rays indicating areas of ongoing star formation in the Galaxy, consistent with the observations by the SPI/INTEGRAL instrument [4]. [1] Côté et al., 2021 Science 371, 945 [2] Wallner et al., 2021 Science 372, 742W [3] Wehmeyer et al., 2023 ApJ 944, 121 [4] Kretschmer et al., 2013 A&A 559, A99

Model-Independent Measurements α-ANCs for the 12C(α,γ)16O Reaction

• Emily Harris (Texas A&M University)

The $^{12}$C(α,γ)$^{16}$O reaction is often considered the “Holy Grail” of nuclear astrophysics. It determines the absolute abundance of $^{12}$C and $^{16}$O in our universe and plays a fundamental role in the late stages of stellar evolution. However, direct measurement of this reaction is not possible with current experimental methods. This is because the Gamow peak at 300 keV is far below the Coulomb barrier where the cross section is on the order of $10^{−17}$ b. Low-energy extrapolations from higher energy measurements have proven challenging for this reaction and thus the reaction rate is not known to the desired uncertainty of 10%. One way to reduce uncertainties related to low-energy extrapolations is an indirect technique that measures Asymptotic Normalization Coefficients (ANCs) of bound states extracted from sub-Coulomb α-transfer reactions. This approach provides a valuable tool for studying astrophysically important reaction rates since the results are nearly model independent. One of the remaining sources of uncertainty for extrapolation is the α-ANC of the ground state of $^{16}$O. The preliminary results of an experiment performed at the Texas A&M University Cyclotron Institute using the TexPPAC detector will be presented for the sub-Coulomb α-transfer reaction of $^{12}$C($^{20}$Ne,$^{16}$O)$^{16}$O.

Dwarf galaxies' view of the heavy elements (Main Conference (May 23 - 26))

• Asa Skuladottir (INAF)

The origin of heavy elements such as europium (Eu), and gold (Au) remains mystery, and the astrophysical site hosting the rapid neutron-capture process (r-process; high neutron flux) remains unclear to this day. With spectroscopic observations of individual stars in the Milky Way and the dwarf galaxy satellites, it becomes clear that (at least) two distinct r-process sites are needed to explain the data: a quick source with timescales comparable to core-collapse supernovae, and a delayed source with characteristic timescales of a few ~Gyr, most probably originating in neutron star mergers. In this talk I will go over the data and the arguments leading to this result and show that only by looking at all the available data in many galaxies will we be able to understand the origin of the heavy elements.

On the Prospects for R-Process Nucleosynthesis in Realistic GRRMHD Collapsars

• Brandon Barker (Michigan State University)

We model a black hole – accretion disk system originating from the circularization of in-falling matter from a collapsing star – the collapsar scenario. We use the new, open source code Phoebus which includes frequency dependent general relativistic radiation magnetohydrodynamics with a dense matter equation of state. Using these improved initial conditions, we access the prospects for rapid neutron capture (r-process) nucleosynthesis occurring in the collapsar disk winds. Moreover, we access whether or not these winds may escape the in-falling stellar mantle and carry away r-process rich ejecta. We present prospects for future work on the sensitivity of these results to properties of the progenitor star.

New experimental decay properties of very exotic neutron-rich nuclei in the north-east of double magic $^{78}$Ni region. First $^{91-93}$Br $\gamma$ ray spectroscopy.

• Roger Caballero Folch (TRIUMF)

The freeze-out of the $r$-process path involves thousands of nuclei decaying to stability by $\beta$-decay through isobaric chains, and $\beta$-delayed neutron emission, the latter forcing a shift of the isobaric chains to lower masses, with a significant effect in the final abundances. The scarce experimental data available in several regions of the nuclei chart is the main uncertainty of the astrophysical models to better understand the observed abundance distribution, since they rely heavily on theoretical data for yet unmeasured nuclei. Since 2016, the BRIKEN collaboration has investigated several neutron-rich regions between $A$=70 and $A$=200 with the aim of determining properties of hundreds of isotopes with unknown or incomplete decay information that were not accessible before. This contribution is part of an experiment focused in the neutron-rich nuclei in the $A\approx$90-100 region with interest for nuclear structure and astrophysics. The aim is to provide new experimental $\beta$-decay half-lives, $\beta$-delayed neutron emission probabilities (P$_{xn}$), and $\gamma$ ray information of north-east nuclei in the vicinity of the double magic $^{78}$Ni. The experimental setup was installed at the fragmentation RIB facility of RIKEN in Japan, and consisted of a DSSDs array to register the implanted ions and $\beta$-decays, and the BRIKEN neutron counter, which also included two HPGe clover-type $\gamma$-ray detectors for high resolution spectroscopy. In this contribution, I will report for the first time information of the $\gamma$ spectroscopy for $^{91-93}$Br nuclei, together with $\beta$-decay half-lives and P$_xn$ values of neutron-rich Ge, As, Se, and Br nuclei around mass A$\approx$90. The implications of the results in theoretical models and astrophysical simulations will also be discussed.

Hitting the Lithium Record with the most Li-Enhanced metal-poor Giant

• Rana Ezzeddine (University of Florida)

Lithium remains to be one of the most ambiguous elements in the Universe. Despite observational and theoretical evidence that lithium (Li) photospheric abundances in low-mass stars decrease as they age due to dregde-up, a small fraction of low-mass red giants exhibit exceptionally high Li abundances. I will report on the exciting discovery of the most Li-enhanced red-giant star to date, with an ultra-high Li abundance of A(Li)(3D,NLTE)= 5.62. I will present a detailed spectroscopic analysis of this star, and discuss evidence of both internal and external enrichment processes tied to its observational signatures. I will discuss how this new benchmark Li star will provide ample opportunities and push within the community to further investigate the origin and evolution of Li in the Galaxy as well as place stronger constraints on 3D mixing models, as we expect current and future high-resolution spectroscopic surveys to discover more such stars.

Experimental determination of the triple alpha rate

• Takahiro KAWABATA (Department of Physics, Osaka University)

The triple alpha reaction is one of the most important nuclear reactions in nucleosynthesis. 3alpha resonance states are formed as intermediate states in the triple alpha reaction. Most of the resonance states decay into the original 3alpha particles, but a tiny fraction of them become the ground state of $^{12}$C via radiative decays. Therefore, the radiative decay widths of the 3lpha resonances are very important parameters to determine the triple alpha rate. Recently, we have measured the radiative-decay width of the $3^-_1$ state in $^{12}$C for the first time, and found that it has a sizable contribution to the triple alpha reaction at high temperatures [1]. We will also report our on-going work to measure the radiative-decay width of the Hoyle state motivated by a striking report that the radiative-decay width of the Hoyle state is about 50% larger than the previous literature value [2]. [1] M. Tsumura, T. Kawabata *et al*., Phys. Lett. B **817**, 136283 (2021). [2] T. Kibedi *et al*., Phys. Rev. Lett. **125**, 182701 (2020).

Measuring the $^{15}$O$(\alpha,\gamma)^{19}$Ne Reaction Rate in Type I X-ray Bursts using $^{20}$Mg $\beta$-decay

• Tyler Wheeler (Michigan State University)

A neutron star can accrete hydrogen-rich material from a low-mass population II binary companion star. This can lead to periodic thermonuclear runaways, which manifests as a Type I X-ray bursts detected by space-based telescopes. Sensitivity studies have shown that $^{15}$O$(\alpha,\gamma)^{19}$Ne carries one of the most important reaction rate uncertainties affecting the modeling of the resulting light curve. This reaction is expected to be dominated by a resonance corresponding to the 4.03 MeV excited state in $^{19}$Ne. This state has a well-known lifetime, so only a finite value for the small alpha-particle branching ratio is needed to determine the reaction rate. Previous measurements have shown that this state is populated in the decay sequence of $^{20}$Mg. $^{20}$Mg($\beta p \alpha$)$^{15}$O events through the key $^{15}$O($\alpha$, $\gamma$)$^{19}$Ne resonance yield a characteristic signature: the emission of a proton and alpha particle. To identify these coincidence events the GADGET II detection system was used at the Facility for Rare Isotope Beams during Experiment 21072. An $^{36}$Ar primary beam was impinged on a $^{12}$C target to create a fast beam of $^{20}$Mg that fed the $^{19}$Ne state of interest. We are presenting here the preliminary results from this experiment, which includes discussion of the data processing and analysis methods being used on the newly acquired data, as well as a primer on the development of convolutional neural networks for rare event identification. This work has been supported by the U. S. Department of Energy under award no: DE-SC0016052 and the U. S. National Science Foundation under award no: 1565546 and 1913554.

Measurements of the Cosmic Ray Nuclei with the Alpha Magnetic Spectrometer (AMS) (Multi-messenger Astronomy for Nuclear Astrophysics Workshop May 25)

• Yi Jia (Massachusetts Institute of Technology)

The Alpha Magnetic Spectrometer (AMS) is a multi-purpose high-energy particle detector installed on the International Space Station on May 19, 2011 to conduct a unique long-term mission of fundamental physics research in space. The primary physics objectives of AMS include the precise studies of the origin of dark matter, antimatter, and cosmic rays as well as the exploration of new phenomena. To date, AMS has collected more than 200 billion charged cosmic rays with energies up to multi TeV. In this talk, I will present the latest AMS results on the measurements of cosmic ray nuclei.

Presolar grains from Core-Collapse Supernovae (Multi-messenger Astronomy for Nuclear Astrophysics Workshop May 25)

• Marco Pignatari (Konkoly Observatory, CSFK)

A fraction of the presolar grains found today in meteorites are identified as relics of old Core-Collapse Supernovae, which exploded shortly before the formation of the Solar System. Their stellar origin can be identified based on their anomalous isotopic abundances, including both stable and radioactive isotopes. These observations are challenging present theoretical stellar models. In this talk I will review some of these challenges, and I will discuss the main properties and the present limitations of the theoretical models that appear to better fit presolar grains measurements.

Detection of Core-Collapse Supernova Neutrinos

• Kate Scholberg (Duke University)

When a massive star collapses at the end of its life, nearly all of the gravitational binding energy of the resulting remnant is released in the form of neutrinos. I will discuss the nature of the core-collapse neutrino burst and what we can learns from the detection of these neutrinos. I will cover supernova neutrino detection techniques in general, current supernova neutrino detectors, and prospects for specific future experiments.

Neutrinos from core collapse supernovae and their multimessenger connections (Multi-messenger Astronomy for Nuclear Astrophysics Workshop May 25)

• Cecilia Lunardini (Arizona State University)

I will illustrate how future detections of supernova neutrinos will inform us on the physics of collapsing stars, with emphasis on the potential of joint analyses with other messengers, in particular gravitational waves. The discussion will include supernovae ranging from cosmological to near-Earth.

The Compton Spectrometer and Imager (Multi-messenger Astronomy for Nuclear Astrophysics Workshop May 25)

• Steven Boggs (University of California, San Diego)

The Compton Spectrometer and Imager (COSI) is a NASA Small Explorer (SMEX) satellite mission in development with a planned launch in 2027. COSI is a wide-field gamma-ray telescope designed to survey the entire sky at 0.2-5 MeV. It provides imaging, spectroscopy, and polarimetry of astrophysical sources, and its germanium detectors provide excellent energy resolution for emission line measurements. Science goals for COSI include studies of 0.511 MeV emission from antimatter annihilation in the Galaxy, mapping radioactive elements from nucleosynthesis, determining emission mechanisms and source geometries with polarization measurements, and detecting and localizing multimessenger sources. The instantaneous field of view for the germanium detectors is >25% of the sky, and they are surrounded on the sides and bottom by active shields, providing background rejection as well as allowing for detection of gamma-ray bursts and other gamma-ray flares over most of the sky. This presentation will include an overview of the COSI mission, including the science, the technical design, and the project status.

Title TBA

• Carla Fröhlich (North Carolina State University)

Prospects for Multimessenger Nuclear Astrophysics with JWST in LVK O4 and Beyond (Multi-messenger Astronomy for Nuclear Astrophysics Workshop May 25)

• Maria Drout (University of Toronto)

Room: Rm 1300 - Auditorium Approximately half of all elements heavier than iron form through rapid-neutron capture. Yet the cosmic origin of these “r-process” elements has been debated for over 60 years. In 2017, the discovery of a kilonova associated with the gravitational wave source GW170817 partially unraveled this mystery---firmly establishing that neutron star mergers do synthesize r-process elements. However, in this discovery's wake many questions remain. In particular, it is unclear whether GW170817 synthesized any of the heaviest “third peak” or actinide elements. As a result, we are still uncertain whether NS mergers are the only – or even the dominant – site of r-process production. However, the recent successful launch of JWST coupled with the imminent start of the LIGO/Virgo/Kagra Observing Run 4 (LVK O4) provide us a unique way to tackle some of these questions. In this talk, I will review JWSTs unique capabilities in the context of predictions for electromagnetic counterparts to neutron star mergers, and highlight a set of JWST programs that will be active during LVK O4. I will highlight both the science they hope to probe and the likelihood of a successful trigger over the next 18 months. Finally, I will emphasize how the scientific outcomes of JWST can be maximized by coupling these observations with those of future, wide-field, UV telescopes.

Heavy Element Nucleosynthesis in the Multi-Messenger Era (Multi-messenger Astronomy for Nuclear Astrophysics Workshop May 25)

• Erika Holmbeck (Carnegie Observatories)

Room: Rm 1300 - Auditorium Neutron star mergers (NSMs) have been confirmed as one of the production sites of the heaviest elements. Studying post-NSM signals in the electromagnetic spectrum is invaluable for understanding the production of these elements, especially as the LIGO Scientific Collaboration begins its next observing run. However, with the current low detection rates of post-merger light curves, we invoke a different kind of resource for observational data: metal-poor stars. Long after merger, metal-poor stars can host in their spectra signatures of the historical events that produced the heavy elements, which can in turn be used as additional sources to study ancient NSM sites. This talk will discuss the overlap between observations of metal-poor stars and NSM signals at this critical time in astronomy and how their joint study can help constrain the cosmic evolution of the elements and the fundamental nature of dense matter.

The Origin of the Elements and their Evolution in Galaxies (Main Conference (May 23 - 26))

• Chiaki Kobayashi (University of Hertfordshire)

Stars are fossils that retain the history of their host galaxies. Elements heavier than helium are created inside stars and are ejected when they die. Elements heavier than iron (such as gold) are also produced by neutron star mergers. From the spatial distribution of elements in galaxies, it is therefore possible to constrain star formation and chemical enrichment histories of the galaxies. This approach, Galactic Archaeology, has been popularly used for our Milky Way Galaxy with a vast amount of data from Gaia and multi-object spectrographs. This approach can also be applied to external galaxies thanks to integral field units. Theoretical predictions are also available including detailed chemical enrichment into hydrodynamical simulations from cosmological initial conditions. These simulations can well reproduce the metallicity distribution in the universe, observed as the mass-metallicity relations of galaxies and metallicity radial and vertical gradients within galaxies. However, very high-redshift observations, such as the fluorine-enhanced galaxy at z=4.4 discovered by ALMA and the nitrogen emission of GN-z11 at z=10.6 taken by JWST/NIRSpec, challenge our current understanding of nuclear astrophysics.

The Force Explosion Condition Accurately Predicts Explodability of Core-collapse Supernova Simulations

• Mariam Gogilashvili (Department of Physics, Florida State University)

At the end of their lives, most massive stars undergo core collapse. Some stars explode as a core-collapse supernova (CCSN) explosion leaving behind neutron stars (NS) while others fail to explode and collapse to stellar-mass black holes (BH). One of the major challenges in CCSN theory is to predict which stars explode and which fizzle. We develop an analytic force explosion condition (FEC) for spherical explosions. The FEC is $\tilde{L}_\nu\tau_g-0.06\tilde{\kappa} > 0.38$ and depends upon two dimensionless parameters only: 1. the dimensionless neutrino heating deposited in the gain region: $\tilde{L}_\nu \tau_g = L_{\nu} \tau_g R_{\rm NS}/ ( G \dot{M} M_{\rm NS})$ and 2.the dimensionless neutrino opacity $\tilde{\kappa} = \kappa \dot{M} / \sqrt{G M_{\rm NS} R_{\rm NS}}$ that parameterizes the neutrino optical depth in the accreted matter near the neutron-star surface. We test and validate the FEC using one dimensional light-bulb simulations as well as one-dimensional simulations with realistic neutrino transport. In addition to being an accurate explosion condition for spherical simulations, the FEC also promises to be a useful diagnostic to measure a "distance" to explosion. These successes suggests that the FEC has potential to be an accurate diagnostic for multi-dimensional simulations as well. We will present progress in validating the FEC with multi-dimensional simulations.

Low energy studies of Mg + Ne fusion for pycnonuclear burning in an accreting neutron star

• Javier Rufino (University of Notre Dame)

Pycnonuclear burning is an important heat source that takes place in the crust of an accreting neutron star. Theoretical models predict that the most important reactions in pycnonuclear burning are neutron rich mass regions of Mg + Mg-, Ne + Ne-, and Mg + Ne-fusion reactions. Pycnonuclear burning is a density driven reaction meaning they occur at very low energies, however, there is a lack of experimental data for these fusion reactions not only for the neutron rich mass regions, but also for the stable mass region. This lack of information leads theoretical fusion calculations to differ by many orders of magnitude in the low energy nuclear regime. To constrain these fusion cross sections and allow models to better extrapolate to low energies an experimental campaign was started to measure Mg + Ne fusion cross sections that start from stable forms of Mg up to neutron rich in Mg. The most recent experiments performed at the University of Notre Dame are two fusion experiments, $^{24}$Mg + $^{20}$Ne and $^{26}$Mg + $^{20}$Ne. We ran both experiments using the Tandem FN accelerator with a $^{24}$Mg beam at 80 MeV, and a $^{26}$Mg beam at 81 MeV , measuring the fusion cross sections using the ND-Cube, an active target time projection chamber, that was filled with a gas mixture of Ne:H$_2$ (95:5). I will present preliminary results from these two experiments as well as an outlook to repeat these experiments optimizing the experiment parameters, and plans for future experiments in the $^{28}$Mg- and $^{30}$Mg- + $^{20}$Ne mass regions at national user facilities.

The impact of Neutron-Star Structure and Cooling on Type-I X-ray Bursts

• Akira Dohi (RIKEN)

Type-I X-ray bursts are rapidly brightening phenomena triggered by the nuclear burning of light elements near the surface of accreting neutron stars. Observed light curves are sensitive to many model parameters such as accretion rate, the composition of accreted matter, reaction rates, neutron star structure, and temperature, and therefore Type-I X-ray bursters are powerful sites to probe uncertainties of many kinds of physics. In this study, we focus on the uncertainties of the equation of states, which determines the latter two properties. Based on our numerical models covering whole areas of neutron stars, we will present their impact on X-ray burst light curves. Furthermore, we will discuss the possibility to constrain EOSs from X-ray regular bursters.

Sensitivity of He Flames in X-ray Bursts to Nuclear Physics

• Zhi Chen (Stony Brook University)

Through the use of an axis-symmetric 2D hydrodynamic simulation, we conducted further investigations into the laterally propagating flames in X-ray bursts (XBRs). We aim to investigate the sensitivity of a pure propagating helium flame to different nuclear reaction networks. We confirmed the phenomenon of enormous energy generation shortly after flame establishment after adding 12C(p, γ)13N(α, p)16O to the network, in agreement with the past literature. The massive energy output of XRBs leads to a short accelerating phase that is crucial to accurately modeling their flame dynamics. Furthermore, we investigate the influence of different plasma screening routines on the He flame propagation. We finally examine the performance of simplified-SDC, a novel approach to hydrodynamics and reaction coupling proposed in our previous paper, in comparison to strang-splitting during XRB simulation.

Direct measurements of (α,n) cross sections relevant for the weak r-process (Main Conference (May 23 - 26))

• Melina Avila (Argonne National Laboratory)

The recent discovery of two binary neutron stars merging has shed light on the production of heavy elements via the rapid neutron capture process (r-process). However, studies of ultra-metal-poor stars indicate that there is more to the story. In fact, there is strong evidence that suggests that another r-process site is responsible for the production of the lightest heavy elements. Potential candidate for producing weak r-process elements are neutrino-driven winds following core-collapse supernova explosions. Unfortunately, only a few reaction rates essential to understanding astrophysical models are currently known due to the small cross sections and difficulties associated with studying low-intensity radioactive beams. However, recent advancements in experimental techniques and capabilities of radioactive ion beam facilities have made it possible to explore these reactions further. In this talk, I will discuss recent experimental efforts to constrain these reactions using the MUSIC detector. This work was supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contract Number DE-AC02-06CH11357. This research used resources of ANL’s ATLAS facility, which is a DOE Office of Science User Facility

High neutron flux, high deuteron and neutron yields from the interaction of a petawatt laser with a cryogenic deuterium jet

• Ou Labun (University of Texas at Austin)

A compact high-flux, short-pulse neutron source would have applications from nuclear astrophysics to cancer therapy. Laser-driven neutron sources can achieve fluxes much higher than spallation and reactor neutron sources by reducing the volume and time in which the neutron-producing reactions occur by orders of magnitude. We report progress towards an efficient laser-driven neutron source in experiments with a cryogenic deuterium jet on the Texas Petawatt laser. Neutrons were produced both by laser-accelerated multi-MeV deuterons colliding with Be or mixed metallic catchers and by d(d, n)3He fusion reactions within the jet. We observed deuteron yields of 10^13/shot in quasi-Maxwellian distributions carrying ∼ 8 − 10% of the input laser energy. We obtained neutron yields greater than 10^10/shot and found indications of a deuteron-deuteron fusion neutron source with high peak flux (> 10^22 cm^−2 s^−1). The estimated fusion neutron yield in our experiment is one order of magnitude higher than any previous laser-induced dd fusion reaction. Though many technical challenges will have to be overcome to convert this proof-of-principle experiment into a consistent ultra-high flux neutron source, the neutron fluxes achieved here suggest laser-driven neutron sources can support laboratory study of the rapid neutron-capture process, which is otherwise thought to occur only in astrophysical sites such as core-collapse supernova, and binary neutron star mergers. Moving forward, we are preparing an experiment for late 2023 to reproduce the high neutron flux and measure for the first time a multi-neutron capture process with 103Rh and 197Au as nuclear waiting materials.

Impact of the experimentally constrained $^{93}$Sr(n,$\gamma$)$^{94}$Sr reaction for the astrophysical $i$-process

• Andrea Richard (Lawrence Livermore National Laboratory)

Neutron-capture cross sections play a vital role in our understanding of heavy element nucleosynthesis. In astrophysical processes such as the intermediate neutron-capture process, or $i$-process, element formation occurs in neutron-rich environments and involves short-lived isotopes for which capture cross sections cannot be measured via direct techniques. Instead reaction rates in these regions rely on calculations that have uncertainties up to a few orders of magnitude. Recent measurements of the $\beta$-decay of $^{94}$Rb, which compared the neutron-to gamma-ray-branching ratio of state decays above the neutron separation energy in $^{94}$Sr, suggest an enhanced $\gamma$-ray branch which would in turn lead to an unexpectedly large $^{93}$Sr(n,$\gamma$) cross section. If confirmed, such an enhancement could have a strong impact on our understanding of $i$-process nucleosynthesis involving nuclei in this region. In order to investigate this potential enhancement of the $^{93}$Sr(n,$\gamma$) cross section and its impact on the $i$-process, an experiment was performed at TRIUMF using an 8 MeV/u $^{93}$Sr beam impinging on a CD$_2$ target. The (d,p$\gamma$) coincidence data was measured using the SHARC and TIGRESS arrays. Experimental details from the measurement of $^{93}$Sr(d,p)$^{94}$Sr will be presented along with preliminary gamma-particle coincidence analysis using the Surrogate Reaction Method along with preliminary $i$-process calculations. *This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.

Constraining the i-process with neutron-capture reaction rates

• Caley Harris (Michigan State University)

The majority of elements heavier than iron are produced via neutron capture processes, primarily the s process and the r process. However, certain astrophysical observations, such as Sakurai’s object and several CEMP stars that show enhancement of s- and r-elements, cannot be described by either process or a combination of the two. The intermediate i process was proposed as a neutron capture process that proceeds at neutron densities between those of the s and r processes, in a region several neutrons away from stability. Models to determine the final abundance pattern of astrophysical environments depend on nuclear physics input, including β-decay rates, nuclear masses, and neutron capture rates. Denissenkov et al. performed a sensitivity study on the neutron capture rates of 52 unstable isotopes and determined eight reactions that had the largest impact on the final abundance pattern of an i process model. Measurements of the neutron capture rates on 85-86Br, 87-89Kr, 89Rb, and 89,92Sr, would significantly reduce the uncertainties. The preliminary results of an experiment performed at Argonne National Lab using the SuN detector, its associated tape station (SuNTAN), and beams from the CARIBU facility will be presented for the indirect study of 87-89Kr(n,γ)88-90Kr. This research was funded by the National Science Foundation Funding Acknowledgement: and used resources of ANL’s ATLAS facility, which is a DOE Office of Science User Facility.

Constraining the 13C(α,n)16O reaction rate with 16O + n total and elastic scattering cross section measurements

• Joseph Derkin (Ohio University)

Stellar nucleosynthesis for a large section of the heavy elements is governed in part by the slow neutron capture process (s-process). The ${}^{13}{\rm C}(\alpha, n) {}^{16}{\rm O}$ reaction is the primary source of neutrons which propels this reaction sequence further along the nuclear chart to produce increasingly heavier isotopes. Many efforts in the community have been made to further constrain this reaction rate, in order to better understand the behavior of the s-process. An intermediate state can be formed during the ${}^{13}{\rm C}(\alpha, n) {}^{16}{\rm O}$ reaction, causing a resonance to appear as an excitation in the ${}^{17}{\rm O}$ compound nucleus. Further measurements are therefore required to refine the ${}^{16}{\rm O}$ total neutron cross section database, leading to a more accurate evaluation of the ${}^{13}{\rm C}(\alpha, n) {}^{16}{\rm O}$ reaction rate. We have identified a number of narrow resonances in the ${}^{16}{\rm O} + n$ reaction channel to be studied using neutron transmission and scattering measurements. Our measurements utilize the newly-installed Fixed Angle Short Trajectory (FAST) reaction-based collimated neutron source at the Edwards Accelerator Laboratory at Ohio University. This presentation includes Monte Carlo simulation results of the FAST neutron source and preliminary results from the first commissioning experiment.

CLOSING REMARKS

• Ruchi Garg (Facility for Rare Isotope Beams, Michigan State University)

Room: Rm 1300 - Auditorium