International Symposium on Nuclei in the Cosmos XVIII (NIC XVIII)

15 Jun 2025, 19:00 → 20 Jun 2025, 13:00 Europe/Brussels

Girona

Jordi José (UPC, IEEC), Laura Tolós (ICE-CSIC, IEEC)

 

*** If you have missed the registration deadline, contact the organizers at nic2025@ieec.cat 

Nuclei in the Cosmos (NIC) is a biennial series of Nuclear Astrophysics conferences. These interdisciplinary events gather together several hundred nuclear physicists, astrophysicists and cosmochemists, to review, share, and discuss recent advances (and challenges) in this field, covering broad areas, from the origin of the elements to the nuclear processes that power stars and their evolution. As such, it has become the most important international meeting in Nuclear Astrophysics. Prior to each edition of the Conference, a School for graduate students and early career researchers is also held.

The series began in 1990, with the conference organized by Heinz Oberhummer and Claus Rolfs in Baden bei Wien, Austria, and changes location in every edition. To date, 17 editions of NIC have taken place in different towns, countries, and continents:

1990 NIC I    Baden bei Wien, Austria
1992 NIC II   Karlsruhe, Germany
1994 NIC III  Gran Sasso, Italy
1996 NIC IV   Notre Dame, USA
1998 NIC V    Volos, Greece
2000 NIC VI   Aarhus, Denmark
2002 NIC VII  Fuji-Yushida, Japan
2004 NIC VIII Vancouver, Canada
2006 NIC IX   CERN, Switzerland
2008 NIC X    Mackinac Island, USA
2010 NIC XI   Heidelberg, Germany
2012 NIC XII  Cairns, Australia
2014 NIC XIII Debrecen, Hungary
2016 NIC XIV  Niigata, Japan
2018 NIC XV   Gran Sasso, Italy
2021 NIC XVI  Chengdu, China (online)
2023 NIC XVII Daejeon, South Korea

NIC XVIII will take place in Girona (Catalonia, Spain) in Summer 2025 (June 15 - 20), and it will be preceded by the usual NIC School in downtown Barcelona, the week before (June 10 - 13).

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Circulars

• First_Circular_NIC2025.pdf
• Second_Circular_NICXVIII.pdf
• Third_Circular_NICXVIII.pdf

Monday 16 June

1 Opening

Speakers: Jordi Jose (UPC), Jordi José (UPC)

NIC XVIII Symposium_JJ.pdf

2 Nuclear Astrophysics: Perspectives and Challenges

Speaker: Roland Diehl

Stellar Abundances I – Spectroscopy, Meteorites, Solar System Abundances, Extremely Metal-Poor Stars

3 Solar System Elemental Abundances

Speakers: Katharina Lodders (Dept of Earth, Environmental, & Planetary Sciences and McDonnell Center for Space Sciences, Washington Univ., St. Louis, MO 63130, USA.), Katharina Lodders, Maria Bergemann (Max Planck Institute for Astronomy, Heidelberg, Germany), Maria Bergemann

10:00 Coffee Break

Stellar Abundances I – Spectroscopy, Meteorites, Solar System Abundances, Extremely Metal-Poor Stars

4 Abundances of EMP stars

Understanding the mass distribution of the first generation of massive stars and the yields of individual elements they injected into the intergalactic medium is one of the central questions in modern astrophysics. Among the most powerful observational clues to address this issue are the elemental abundance patterns of extremely metal-poor (EMP) stars. These stars are believed to have formed from gas clouds enriched by a small number of supernova events and have preserved the chemical signature of those events to the present day. As such, they provide a unique opportunity to empirically constrain the nucleosynthetic yields of individual supernovae.
Over the past decade, wide-field photometric and spectroscopic surveys of the Milky Way's stellar populations have efficiently identified these rare EMP stars. Follow-up high-resolution spectroscopic observations allow detailed statistical analyses of their elemental abundance patterns. In this talk, I will review what we have learned about nucleosynthesis and chemical evolution in the early universe based on results from these investigations. I will also present prospects for ongoing, wide-field surveys targeting Galactic stellar populations.

Speaker: Dr Miho Ishigaki (National Astronomical Observatory of Japan)

5 Deriving Progenitors of Extremely Metal-poor Stars with Nucleosynthesis Yields of Massive Stars

The most metal-poor stars offer a unique window into the chemical enrichment processes driven by Population III stars in the early Universe. The observed chemical abundance patterns in these stars provide critical constraints on the nucleosynthetic yields of metal-free progenitors, shedding light on their zero-age main-sequence masses. In this work, we analyze 406 very metal-poor stars with the latest high-resolution spectroscopic data from LAMOST and Subaru, presenting the most extensive investigation to date of the initial mass distribution of the first stars. The results challenge the traditional Salpeter initial mass function. By incorporating supernova explodability theory, we propose a modified power-law function that successfully accounts for the observed mass distribution, emphasizing that the initial metal enrichment arose predominantly from successful supernova explosions. Our findings suggest an extremely top-heavy or nearly flat initial mass function for Population III stars, characterized by a high explosion energy exponent. This study highlights the critical role of the nucleosynthesis in massive stars and explosion mechanisms in shaping the chemical evolution of the early Universe.

Speaker: Ruizheng Jiang (National Astronomical Observatories, CAS)

6 The heavies in CEMP

Elements heavier than iron are predominantly formed through neutron-capture processes, the slow (s-process) and rapid (r-process) neutron-capture processes. The s-process occurs in low- and intermediate-mass stars during the Asymptotic giant branch stage, while the r-process takes place under more extreme conditions, such as neutron star or black hole mergers.

Recently, an intermediate neutron-capture process (i-process) has been proposed to explain the dual s- and r-process enrichment observed in carbon-enhanced metal-poor (CEMP-r/s) stars. However, the astrophysical site of the i-process remains uncertain. Previous studies suggested that CEMP-r/s stars could have been enriched by a low-mass, low-metallicity thermally pulsing asymptotic giant branch (TP-AGB) companion undergoing i-process nucleosynthesis triggered by proton ingestion during its first convective thermal pulses. These conclusions were based on abundance measurements of several lanthanides and heavy elements such as lead (Pb).

Here, for the first time, we determine the abundances of very heavy r-process elements, including terbium (Tb), holmium (Ho), thulium (Tm), tantalum (Ta), iridium (Ir), lutetium (Lu), and ytterbium (Yb). These new measurements are compared with nucleosynthesis model predictions, providing further insights into the i-process and its role in heavy-element enrichment.

Speaker: Sophie Van Eck (Université libre de Bruxelles)

7 Nucleosynthetic Isotope Variations in Meteorites

Speaker: Larry Nittler (Arizona State University)

8 Examinating evidence for a shorter $^{146}$Sm-$^{142}$Nd chronology in the early solar system

$^{146}$Sm, as an extinct p-process isotope, plays an irreplaceable role in the time-line construction of the early solar system (ESS) and the geochemical tracing via its α decay to $^{142}$Nd. Persistent debate on both measured and theoretical half-lives of $^{146}$Sm results in a large uncertainty in the initial $^{146}$Sm abundance of the ESS and subsequent dating of planetary events after the birth of the Sun. In this study, a newly-proposed technique was used to analyze the α decay process within the widely-employed α-core nuclear potentials, namely, three different Woods-Saxon shapes and the double-folding potential. The half-life is obtained through large-scale random sampling of parameters for each potential, with the robust results subjected to statistical analysis. Additionally, a well-founded extrapolation for α decay energy of $^{146}$Sm, based on the systematic behavior of the neighboring decay chain, is in perfect agreement with the adopted experimental value, further supporting the present evaluation on this crucial half-life. As a result, the half-life of $^{146}$Sm was determined to be 71.74 ± 7.39 million years with a 95% confidence interval. The initial $^{146}$Sm/$^{144}$Sm ratio of 0.0092 ± 0.0014 at 4568 (± 10) Ma, corresponding to the formation of the solar system, is then determined, further leading to a reduced timescale for various planetary silicate mantle differentiation events of the ESS. It is expected that this study paves the way for a theoretically calibrated $^{146}$Sm-$^{142}$Nd chronometer in future studies of nucleosynthesis, earth and planetary astrophysics.

Speaker: Yibin Qian (Nanjing University of Science and Technology)

9 FLASH Poster Session I

13:00 Lunch Break

Stellar Abundances I – Spectroscopy, Meteorites, Solar System Abundances, Extremely Metal-Poor Stars

10 R-Process Alliance: unveiling the abundance patterns of ten r-II stars through homogeneous spectral analysis

The rapid neutron capture process, known as the $r$-process, is responsible for producing approximately half of the elements heavier than iron, including Ag, Au, Th and U, among others. Despite its fundamental role in nucleosynthesis, the astrophysical sites and conditions of the r-process remain an open question. Metal-poor stars serve as exceptional
laboratories for studying this process, as their chemical compositions reflect that of the cloud in which they were born.
Among them, $r$-II stars, which are characterized by strong enhancements in $r$-process elements with [Eu/Fe] > 0.7, offer key insights into the nature of the astrophysical events responsible for heavy element production. However, previous studies have focused on individual $r$-II stars rather than performing a homogeneous analysis of a larger sample.

In this work, we present the first homogeneous chemical abundance analysis of a sample of ten $r$-II stars, expanding upon the discoveries from the R-Process Alliance’s first data release by Hansen et al. (2018) and Sakari et al. (2018). We derive abundances for 28 neutron-capture elements, covering the full $r$-process pattern from Sr to U. A central objective of this study is to determine whether the observed star-to-star variations in $r$-process abundances originate from intrinsic astrophysical differences, such as variations in the progenitor events, or from observational uncertainties.

Our analysis highlights two key elemental regions. (i) the Ru-Ag region, where recent studies suggest signatures of fission fragment deposition (Roederer et al. 2023), and (ii) the third $r$-process peak elements, Os and Ir, which remain poorly explored.

By applying a uniform methodology, we provide the most comprehensive abundance analysis of $r$-II stars to date, enabling a direct comparison across the sample. This approach is essential for bridging observations with theoretical nucleosynthesis models and advancing our understanding of the astrophysical sites of the $r$-process.

Speaker: Mila Racca (Stockholm University)

11 3D NLTE abundance of iron-peak and neutron-capture elements within GCE context

One of the prime questions in Galactic archeology is how chemical elements formed in the universe. Whereas the past decades have focused on nucleosynthesis in single stars, more evidence is emerging in favour of exotic systems such as stripped massive binaries, magnetorotating supernovae (MRSNe) and compact binary mergers with GW detectors. In this study, for the first time, we explore constraints on Galactic chemical enrichment of iron-peak (Mn, Co, Ni) and neutron-capture (Sr, Y, Ba, Eu) elements using data calculated with novel 3D Non Local Thermodynamic Equilibrium (NLTE) models. These elements correspond to key iron-peak, 1st and 2nd s-process peaks, as well as r-process. We contrast the abundance trends for the calculated elements with galactic chemical evolution (GCE) model predictions and constrain the contribution of diverse sites to the nucleosynthesis of these elements. Among the most intriguing findings is the remarkable increase of [Ni/Fe] ratios in the metal-poor stars, accompanied by the well-known rise of [Co/Fe] ratios at low metallicities with decreasing [Fe/H], with values that are significantly [X/Fe] >> 0 at [Fe/H] < -3. These trends could be explained either by a significantly non-standard IMF or a much greater contribution of electron-capture SNe (ECSNe) or hypernovae to the chemical enrichment of the galaxy.

Speaker: Nicholas Storm (Max-Planck-Institute for Astronomy)

12 Nature's Fission Fragment Distribution

The nuclear mechanism responsible for roughly half of the heavy-elements (Z>30) abundances in our Solar system---the rapid neutron capture (r) process---was long thought to produce a "universal" abundance pattern. However, recent studies have challenged r-process universality by identifying significant variations between the elemental abundances patterns of metal-poor ([Fe/H]<$-$1.0), r-process-enhanced stars. In particular, r-process-rich ([Eu/Fe]>+0.3) stars show a signature that may possibly only be explained by fission. In this work, we construct a method of decomposing stellar abundance patterns into a basis set of patterns from which each star can be constructed as a linear combination, akin to a principal component decomposition. We use this method to uncover the underlying signature that is present in the r-process-rich stars in order to derive an empirical record of fission in the r-process. This talk will present the "pure" fission pattern is that is recovered from these metal-poor stars.

Speaker: Erika Holmbeck (Lawrence Livermore National Laboratory)

Nuclear Reactions – Experiments

13 The Beta-Oslo Method and Neutron-Capture Reactions

Great progress has been made regarding our understanding of heavy-element nucleosynthesis in recent years. In particular, the 2017 discovery of a neutron-star merger with its kilonova confirmed that such astrophysical sites can produce heavy elements through the rapid neutron-capture process. At the same time, as more and more high-quality observations become available, the heavy-element nucleosynthesis puzzle becomes more and more complex. For example, some very old stars in the Galactic halo show peculiar element distributions that might only be explained invoking an intermediate neutron-capture process.

In this talk, I will discuss some aspects of the rapid and intermediate neutron-capture processes and the needed nuclear-physics input, with particular emphasis on neutron-capture rates important for abundance calculations. I will also present experimental efforts to obtain indirect constraints of these rates by means of the Oslo method and the beta-Oslo method.

Speaker: Prof. Ann-Cecilie Larsen (University of Oslo)

14 Determining neutron-induced reaction cross sections with surrogate reactions in inverse kinematics at heavy-ion storage rings

Neutron-induced reaction cross sections of short-lived nuclei are essential in astrophysics. In particular, neutron-induced fission cross sections are essential as fission sets the end of the r-process path and influences the abundance patterns and light curves. However, these cross sections are very difficult or impossible to measure due to the difficulty to produce and handle the necessary radioactive targets. The NECTAR (Nuclear rEaCTions At storage Rings) project uses for the first time surrogate reactions in inverse kinematics at a heavy-ion storage ring. This allows one to measure the de-excitation probabilities as a function of the excitation energy of the nuclei formed through the surrogate reaction with unrivaled precision and indirectly determine the aforementioned cross sections.

In this contribution I will present the first results of the NECTAR surrogate-reaction experiment that took place in June 2024 at the ESR storage ring of the GSI/FAIR facility in Darmstadt. In this experiment, the $^{238}$U(d,d') and $^{238}$U(d,p) surrogate reactions were used to form the $^{238}$U and $^{239}$U compound nuclei, respectively, and measure for the first time the fission, γ-ray, neutron and even two- and three-neutron emission probabilities simultaneously. The measurement of all the decay channels competing with fission will allow us to precisely determine fundamental quantities such as fission barriers, particle transmission coefficients, γ-ray strength functions and nuclear level densities and to infer the $^{237,238}$U(n,f), $^{237,238}$U(n,g), $^{237,238}$U(n,n’), $^{238}$U(n,2n) and $^{238}$U(n,3n) cross sections.

Acknowledgment: This work is supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (ERC-Advanced grant NECTAR, grant agreement No 884715).

Speaker: Camille Berthelot (LP2I (ex-CENBG), Bordeaux, France)

15 FLASH Session II

16:15 Coffee Break

Nuclear Reactions – Experiments

16 Role of Exotic Nuclei Away from Stability

The synthesis of heavy elements such as gold and uranium remains one of the profound mysteries in astrophysics. These elements are believed to form through rapid neutron capture reactions (r-process) occurring in extreme astrophysical environments. To unravel this process, it is crucial to understand the properties of thousands of neutron-rich nuclei (Ris) produced during r-process nucleosynthesis. Key parameters such as RI masses, half-lives, and beta-delayed neutron emission probabilities are essential for elucidating elemental abundances in solar systems, metal-poor stars, and meteorites, as well as for identifying the astrophysical sites of r-process events, such as supernovae and binary neutron star mergers.
Over the past decades, significant experimental efforts have been dedicated to studying neutron-rich nuclei that play critical roles in the r-process. This talk will present a series of experimental programs conducted at the Radioactive Isotope Beam Factory (RIBF), focusing on the behavior of these nuclei and their impact on r-process nucleosynthesis.

Speaker: Dr Shunji Nishimura (RIKEN)

17 Experimental investigation on the γ-emission probability of the unbound states in 131Sn through 130Sn(d,p)131Sn reaction measurement for understanding r-process

The rapid neutron capture process, r-process, is responsible for the production of more than half of the elements heavier than iron. However, the physical conditions and astronomical sites of the r-process have not yet been determined. One key issue is the lack of experimental data on the properties of involved exotic nuclei, partly due to the difficulty of measuring neutron capture reactions for short-lived nuclei.
One of the critical isotopic regions in r-process is the area near $^{132}$Sn, which has the neutron magicity with 82 neutrons. A drastic decrease in the neutron capture rate when crossing the neutron magic number is expected for the compound neutron capture due to the large energy gap after the shell closure. Due to a lack of experimental data, there are large uncertainties in neutron capture rates, which result in the large ambiguity in r-process conditions and make the calculation of final elemental abundance of r-process undetermined.
The neutron capture rates can usually be determined with the knowledge of $\gamma$-emission probabilities of the neutron unbound states. However, the low $\gamma$-emission probabilities and usually low $\gamma$-ray detection efficiency have been the experimental obstacles. At the OEDO-SHARAQ beamline in RIKEN RIBF, an alternative method to identify experimental $\gamma$-emission probability was developed, in which the heavy reaction residues are identified with the SHARAQ spectrometer, and the $\gamma$-emission probability can be obtained based on the number of heavy residues with increased neutron number. A $^{130}$Sn(d,p) experiment was conducted with this method to identify the $\gamma$-emission probabilities of the neutron unbound states in $^{131}$Sn. The kinetic energy of $^{130}$Sn beam was degraded to about 20 MeV/u for the one neutron transfer reaction at OEDO beamline. We identified Sn isotopes with A = 129, 130, and 131, which correspond to two, one, and zero neutron emissions after the reaction, respectively, and the $\gamma$-emission probability near the one-neutron separation energy of $^{131}$Sn was explored. The features and preliminary results of this experiment will be presented.

Speaker: Thomas Chillery (LUNA, LNGS)

18 The results of the $^{204}$Tl and $^{205}$Tl neutron capture cross section measurement at n_TOF (CERN) and their impact to the s-process-only $^{204}$Pb and $^{205}$Pb production

Neutron capture cross sections are one of the key input parameters for an accurate description of the slow (s) process of stellar nucleosynthesis, which is responsible for the production of about half of the elemental solar abundances between Fe and Bi in AGB stars [1]. In this contribution we will present the results of the measurement of the capture cross section of the thallium isotopes $^{204}$Tl and $^{205}$Tl, performed at the n_TOF facility (CERN) between 2015 and 2018, and the implications that the new cross section data have for the production of the important s-process only lead isotopes $^{204}$Pb and $^{205}$Pb.

It is well-known that the s-process of elements heavier than Sr occurs in the Asymptotic Giant Branch (AGB) stage of low mass (1.5 to 3 solar masses) stars [1]. In the short, but intense, neutron irradiation taking place in the recurrent Thermal Pulse episodes, both thallium isotopes become unstable with very short half-lives, and thus they act as branching points of the s-process flow, i.e. nuclei in which capture reactions compete with the decay process. Consequently, the capture cross section of both isotopes strongly affects the s-process abundance of their daughter isotopes, which in the case of $^{204}$Tl is $^{204}$Pb. The s-only stable isotopes such as $^{204}$Pb play a pivotal role in studying the s-process, because they can be used to benchmark state-of-the-art AGB models by comparing nucleosynthesis calculations with observed abundances of these nuclei. A new calculation of the stellar $^{204}$Tl$(\mathrm{n},\gamma)$ cross section, based on the results of the first ever measurement of $^{204}$Tl$(\mathrm{n},\gamma)$ conducted at n_TOF, and the consequences of this result for the $^{204}$Pb production in AGB stars were all reported in a recent publication in Physical Review Letters [2]. With the new results, the uncertainty arising from the $^{204}$Tl$(\mathrm{n},\gamma)$ cross-section on the s-process abundance of $^{204}$Pb could be reduced from $\sim$30\% down to +8\%/ -6\%, and the s-process calculations are in agreement with the latest solar $^{204}$Tl solar abundance of Pb reported by K. Lodders in 2021 [3]. Therefore, presently there is no need to invoke additional nucleosynthesis mechanisms or fractionation effects in order to explain the $^{204}$Pb abundance observed in the solar system.

In the case of $^{205}$Tl, the activation of its bound state beta decay to $^{205}$Pb at stellar temperatures makes the $^{205}$Pb abundance very sensitive to the cross section of the $^{205}$Tl$(\mathrm{n},\gamma)$ reaction. Apart from being s-only, $^{205}$Pb is radioactive with a long half-life of 17.2 Myr, and therefore it has potential to be used as a cosmochronometer of the s process. Recently, the results of the first ever measurement of the stellar decay of $^{205}$Tl, conducted at GSI, were published by Leckenby et al. in Nature [4]. The new results allowed the authors to make the first accurate estimation of the s-process isolation time based on s-process calculations and the current $^{205}$Pb meteoritic abundance. In this context, the latest results of the new measurement of the stellar $^{205}$Tl$(\mathrm{n},\gamma)$ cross section that will be presented in this contribution will permit to further reduce the still relevant nuclear data uncertainty affecting the $^{205}$Pb s-process stellar production.

[1] F. Käppeler, R. Gallino, S. Bisterzo, and W. Aoki, Rev. Mod. Phys. 83, 157 (2011).
[2] A. Casanovas-Hoste et al., Phys. Rev. Lett. 133, 052702 (2024).
[3] K. Lodders, Space Sci. Rev. 217, 44 (2021).
[4] G. Leckenby et al., Nature 635, 321 (2024).

Speaker: Adrià Casanovas (Universitat Politècnica de Catalunya (UPC))

19 Underground Measurements of $^{14}$N(p,$\gamma$)$^{15}$O and Other Key Reactions for Nuclear Astrophysics

The LUNA (Laboratory for Nuclear Astrophysics) collaboration has a long and successful history in measuring the cross sections of astrophysically important reactions in a deep underground location at LNGS, Italy. In addition to the very prolific LUNA-II 400 keV accelerator, the collaboration has an extensive program on the recently launched Bellotti Ion Beam Facility (BIBF), which is based on a 3.5 MeV accelerator at LNGS.

The first completed experimental campaign at BIBF was the study of $^{14}$N(p,$\gamma$)$^{15}$O, the key reaction of the CNO cycle hydrogen burning. In this talk, the experimental methods and some preliminary results of the $^{14}$N(p,$\gamma$)$^{15}$O cross section measurement will be presented. In addition, some recent results and ongoing activities of the LUNA collaboration will also be advertised shortly.

Speaker: Gy. Gyürky (HUN-REN Institute for Nuclear Research (ATOMKI))

20 Underground Measurements of the 16O(p,γ)17F Reaction at LUNA

The $^{16}$O(p,$\gamma$)$^{17}$F reaction is the slowest proton-induced reaction in the CNO cycle because at energies of astrophysical interest it has no resonances, making it an example of a pure direct capture reaction. The ratio of $^{16}$O/$^{17}$O in AGB stars depends strongly on the rate of this reaction. This ratio is an important probe of nucleosynthesis and mixing processes in the interior of these stars, as it can be measured directly. At low energies, i.e. centre of mass energies below around 500 keV, there is little experimental data for this reaction, and the data that exists has relatively large uncertainties. In addition, Bayesian estimations of the reaction S-factors carried out by Iliadis et al. in 2022 do not closely match the low energy experimental data, particularly for direct capture to the ground state.

An experimental campaign has been carried out at the LUNA underground accelerator at Gran Sasso National Laboratory in Italy, aiming to measure the cross section for $^{16}$O(p,$\gamma$)$^{17}$F. The very low background in the underground laboratory combined with lead shielding allows for direct measurements of this weak reaction to be carried out at low energies.

The experiment was carried out in two parts, using two different techniques: the prompt gamma rays from the reaction were detected using two CeBr$_{3}$ scintillators and a HPGe detector; and the $\beta$$^{+}$ decay of the resulting $^{17}$F was measured using a segmented BGO detector (the activation method).

I will report on the setup and data taking, and will present the results.

Speaker: Duncan Robb (The University of Edinburgh)

21 FLASH Session III

Tuesday 17 June

Nuclear Reactions – Experiments

22 Direct measurement of the carbon-carbon fusion cross section at stellar energies

The carbon-carbon fusion reaction serves as a crucial reaction for stellar evolution and explosive events, significantly influencing the evolution of massive stars and the explosion of superburst in the Universe. Despite decades of research, there remains considerable uncertainty in the cross section, particularly at stellar energies below E_{C.M.}=3MeV. The extrapolation techniques cannot provide a clear picture of the reaction within the Gamow window. We measured the cross section of ^{12}C(^{12}C,a_{0})^{20}Ne in the energy range of E_{C.M.}=2.3 MeV to 3.6 MeV using an intense carbon beam with intensity up to 100 particle microamperes, provided by the LEAF accelerator in Lanzhou, and a novel detection system comprising a time projection chamber (TPC) and a silicon detector array. Our direct measurement results yield new values for the reaction cross section, indicating that further improvements are needed in the THM indirect method. A new reaction rate is recommended based on our experimental result.

Speaker: Yunzhen Li (Institute of Modern Physics)

23 Investigation of $^{31}$P levels near the proton threshold by Nuclear Resonance Fluorescence and the impact on the $^{30}$Si(p,$\gamma$)$^{31}$P thermonuclear rate

Globular clusters represent fascinating puzzles for understanding stellar evolution and early galaxy formation. Anticorrelations between Mg and K have been observed in a small number of globular clusters, foremost of which is NGC 2419. It has been shown that the observed abundances of Mg and K were likely produced in a progenitor object, before the current generation of stars. The astrophysical environment of this progenitor nucleosynthesis has not yet been determined. One of the important reactions that can help constrain the potential nucleosynthesis environment is the $^{30}$Si(p,$\gamma$)$^{31}$P reaction, where rate uncertainties are still significant in the associated temperature range of interest.

Using the nuclear resonance fluorescence (NRF) technique, we investigated the nuclear structure of $^{31}$P near the proton threshold to refine the properties of key resonances in the $^{30}$Si(p,$\gamma$)$^{31}$P reaction. The experiment was conducted using the High Intensity $\gamma$-ray Source (HI$\gamma$S) at the Triangle Universities Nuclear Laboratory (TUNL). Excitation energies, spins, and parities were determined for several states, including two unobserved resonances at $E_r$ $=$ $18.7$ keV and $E_r$ $=$ $50.5$ keV. Our presented results provide a significant update to the $^{30}$Si(p,$\gamma$)$^{31}$P thermonuclear reaction rate, which is substantially lower than previous estimates at temperatures below $200$ MK, affecting predictions for silicon isotopic abundances in stellar environments.

This work is supported by the DOE, Office of Science, Office of Nuclear Physics, under grants DE-FG02-97ER41041 (UNC) and DE-FG02-97ER41033 (TUNL).

Speaker: David Gribble (UNC Chapel Hill, Triangle Universities Nuclear Laboratory)

Atomic and Nuclear Inputs for Nuclear Astrophysics

24 Atomic Physics Inputs for Kilonova Modelling

With the recent detection of multiple neutron star merger events, the necessity for a more comprehensive understanding of nuclear and atomic properties, as well as radiative transfer processes, has become increasingly critical. Despite advancements in our knowledge, significant uncertainties persist in opacity calculations, leading to variations in the strength and location of spectral features in radiative transfer models. These uncertainties hinder the definitive identification of r-process nucleosynthesis products.

Additionally, observations with the James Webb Space Telescope (JWST) yielded numerous spectral features at infrared wavelengths, with proposed explanations ranging from a cool continuum to forbidden line emission. Due to their intricate atomic structures, Lanthanide ions are promising candidates among these forbidden emission lines, which dominate the cooling processes from approximately one week post-merger in the kilonova evolution and which are essential for non-local thermodynamic equilibrium (NLTE) radiative transfer. However, this is only the first step towards full NLTE-radiative transfer, which will be required to model future kilonova observations.

In my presentation, I will discuss both the current and future needs from atomic physics for radiative transfer modeling of kilonovae. In particular, I will reflect on the required accuracy of atomic properties, large-scale atomic structure calculations, and key challenges associated with the non-local thermodynamic equilibrium (NLTE) radiative transfer necessary for connecting neutron star merger models with astronomical observations.

Speaker: Andreas Flörs (GSI Helmholtzzentrum for Heavy Ion Research)

25 Mass Measurements of Exotic Neutron-Deficient Nuclides Below $^{100}$Sn at IGISOL and Their Astrophysical Implications

The investigation of heavy N = Z nuclei and their neighbors has attracted significant attention both theoretically and experimentally due to their crucial role in nuclear structure studies and their substantial impact on modelling nuclear astrophysical processes, particularly as inputs for the astrophysical rapid proton-capture (rp) and $\nu$p processes [1-3]. Recent advancements at the IGISOL facility in Finland have enabled direct mass measurements of highly exotic neutron-deficient nuclides, specifically around the N=50 shell closure below $^{100}$Sn [4-5].

Using the JYFLTRAP double Penning trap [6], coupled with the newly commissioned inductively heated hot-cavity catcher laser ion source at IGISOL, we have successfully measured the atomic masses of $^{95-97}$Ag [5]. This setup allows the production of very exotic neutron-deficient nuclides. The ground state masses of $^{95-97}$Ag and the low-lying isomeric state in $^{96}$Ag were determined with the JYFLTRAP, achieving a precision of approximately 1 keV/c$^2$. Both the conventional time-of-flight ion-cyclotron resonance (TOF-ICR) method [6] and the phase-imaging ion-cyclotron-resonance (PI-ICR) technique [7-9] were employed in these measurements. This allows us to reevaluate the thermonuclear reaction rate of a few reactions along the rp-process path and its influence on the astrophysical rp process. Additionally, a fusion-evaporation method using a $^{58}$Ni primary beam on a $^{28}$Si target was employed to produce ions of interest in the A = 84 region, with mass measurements conducted using Multi-Reflection Time-of-Flight Mass Spectrometer (MR-TOF MS). These masses will help shed light on the Zr-Nb cycle in the rp process [1] and address some of the major uncertainties in the $\nu$p process. Preliminary results of this experiment will be presented.

This contribution will cover the latest results and progress from our mass measurement campaigns of exotic neutron-deficient nuclides using MR-TOF MS and JYFLTRAP at IGISOL.

Reference
[1] H. Schatz et al., Phys. Rep. 294, 167 (1998).
[2] H. Schatz et al., Phys. Rev. Lett. 86, 3471 (2001).
[3] C. Frohlich et al., Phys. Rev. Lett. 96, 142502 (2006).
[4] M. Reponen et al., Nat Commun 12, 4596 (2021).
[5] Z. Ge, M. Reponen et al., Phys. Rev. Lett. 133, 132503 (2024).
[6] T. Eronen et al., Eur. Phys. J. A 48, 46 (2012).
[7] S. Eliseev et al., Phys. Rev. Lett. 110, 082501 (2013).
[8] D. A. Nesterenko et al., Eur. Phys. J. A 54, 154 (2018).
[9] D. A. Nesterenko et al., Eur. Phys. J. A 57, 11 (2021).

Acknowledgement:
We thank the support from: Academy of Finland under the projects No. 354589, No. 345869 and No. 354968; European Union's Horizon 2020 research and innovation program under grant No. 771036 (ERC CoG MAIDEN) and No. 861198-LISA-H2020-MSCA-ITN-2019

Speaker: zhuang ge (University of Jyväskylä)

26 Comprehensive Atomic Data for Kilonova Spectral Modeling Beyond the Photospheric Phase

The limited but growing set of kilonova observations following neutron star mergers has established these events as significant sites for r-process nucleosynthesis [1,2]. Despite recent advances in spectral identification of several elements in merger ejecta [see for e.g. 3], precise abundance determinations remain challenging, particularly at later evolutionary phases where non-local thermodynamic equilibrium (non-LTE) effects become dominant [4-6]. Our work addresses this challenge through expanded atomic calculations for lanthanide and actinide species, with special attention to processes critical in the low-density environments of expanding ejecta.

We utilize both the Flexible Atomic Code [7] and AUTOSTRUCTURE [8], enhancing atomic structure accuracy through our sequential model-based optimization methodology [9,10]. For selected lanthanides, actinides, and key elements identified in early kilonova spectra, we develop comprehensive datasets that include forbidden transitions and electron impact excitation often omitted in current models. Our analysis demonstrates how synthetic spectra are significantly affected when these transitions are neglected or when atomic processes are approximated using simplified formulae. This can lead to misidentification of spectral features, highlighting the importance of comprehensive atomic datasets for reliable kilonova modeling.

[1] Abbott et al. Astrophys. J. 848, L13 (2017)
[2] Levan et al. Nature 626, 737–741 (2024)
[3] Gillanders et al. MNRAS 529, 2918–2945 (2024)
[4] Gillanders et al. MNRAS stac1258 (2022)
[5] Vieira et al. Astrophys. J. 962, 33 (2024)
[6] Pognan et al. MNRAS 510, 3806 (2022)
[7] Gu et al. Can. J. Phys. 86, 675 (2008)
[8] Badnell Astrophys. Source Code Libr. ascl:1612.014 (2016)
[9] Flörs et al. MNRAS 524, 3083 (2023)
[10] Ferreira da Silva et al. arXiv:2502.13250 (2025)

Speaker: Ricardo Ferreira da Silva (LIP/FCUL)

10:00 Coffee Break

Stellar Abundances II – Presolar Grains

27 Presolar Grains as Probes of Type II Supernova Nucleosynthesis

Presolar grains, submicron- to micron-sized meteoritic particles, originate from stellar winds and the ejecta of stellar explosions, providing direct samples of stellar material. Among these, silicon carbide (SiC) grains are particularly well-studied. Multielement isotope analyses of presolar SiC grains have firmly linked their origins to asymptotic giant branch (AGB) stars and core-collapse Type II supernovae (CCSNe) [1]. While AGB stars account for the majority of presolar SiC grains (>90%), CCSNe contribute a smaller fraction, including X, C, and D grains [1,2]. Additionally, all presolar silicon nitride (Si₃N₄) grains exhibit isotopic similarities to X SiC grains, indicating a shared origin in CCSN ejecta [2].

In this study, we conducted a comprehensive survey of isotope ratios (C, N, Si, Mg, S, Ca, Ti, Fe, and Ni) in presolar CCSN SiC and Si₃N₄ grains extracted from the Murchison meteorite using secondary ion mass spectrometry. High spatial resolution (~100–200 nm) imaging enabled the suppression of contamination and the extraction of intrinsic isotopic signatures [3,4]. Our dataset includes: (i) C, N, Si isotope and initial 26Al/27Al data from 39 X and one C SiC grain, as well as four Si₃N₄ grains [4]; (ii) initial 32Si/28Si ratios from two X grains and the C grain [5]; (iii) Ca isotope data from all four Si₃N₄ grains and the C grain [6]; (iv) Ti isotope data from 25 X grains [7]; and (v) Fe and Ni isotope data from 19 X grains and the C grain. The initial 26Al/27Al and 32Si/28Si ratios assume that 26Mg and 32S excesses, relative to terrestrial Mg and S isotope ratios, are the result of in situ 26Al (t1/2 = 0.72 Ma) and 32Si (t1/2 = 150 a) decay, respectively.
These data reveal several key findings: (i) anti-correlated 26Al/27Al and 30Si/28Si ratios in X and Si₃N₄ grains [4]; (ii) significant 46Ca excesses in the C and Si₃N₄ grains; (iii) the initial presence of 63Ni (t1/2 = 100 a) in C and X grains; and (iv) contrasting Ni isotopic patterns between C and X grains. The Ti isotope data for X grains align with previous findings and suggest that 49V (t1/2 = 330 d) fully decayed to 49Ti before grain condensation [8], thus supporting their late formation in CCSN remnants post-explosion.

We compared our results with CCSN model predictions [9,10], as well as with an analytic model for neutron bursts in the He/C zone [11] that allows for rapid testing of uncertainties in (n,γ) cross sections and stellar parameters. Our data-model comparisons indicate that X and C SiC and Si₃N₄ grains sampled material from at least the He/C, Si/S, and Fe/Ni zones of their parent CCSNe, reflecting nucleosynthesis products from large-scale, selective mixing across CCSN shells [2]. The multielement data require higher-than-solar Ti/Si, Ca/Si, and Ni/Si ratios in the 28Si-rich Fe/Ni zone, challenging the proposal of local mixing across the He shell in [12]; the model of [12] predicts the presence of a 28Si-rich C/Si zone at the bottom of the He shell that is produced by alpha captures at an unusually high density and temperature. Furthermore, the contrasting Ni isotopic patterns between C and X grains require that C grains originated from more energetic CCSNe, ruling out the hypothesis that C and X grains came from the same or similar CCSNe but C grains sampled lower proportions of material from the Si/S and Fe/Ni zones than X grains.

In conclusion, our multielement isotope dataset provided stringent constraints on the nucleosynthetic processes produced by neutron bursts, nuclear statistical equilibrium, and alpha-rich freezeouts in CCSNe. However, due to significant uncertainties in the (n,γ) cross sections of 32Si, 41Ca, and 45Ca, new nuclear experiments are needed to refine model predictions and further elucidate the large-scale mixing processes in the parent CCSNe of these grains.

References:
[1] Liu N. (2025) Book chapter in Treatise on Geochemistry (3rd) 7, 113.
[2] Liu N. et al. (2024) Space Science Reviews 220, #88.
[3] Liu N. et al. (2021) The Astrophysical Journal Letters 920, L26.
[4] Liu N. et al. (2024) The Astrophysical Journal Letters 961, L22.
[5] Liu N. et al. (2024) 86th Annual Meeting of the Meteoritical Society Meeting, Abstract #6020.
[6] Liu N. et al. (2024) 55th Lunar and Planetary Science Conference, Abstract #1478.
[7] Liu N. et al. (2024) 54th Lunar and Planetary Science Conference, Abstract #2496.
[8] Liu N. et al. (2018) Science Advances 4, eaao1054.
[9] Bojazi M.J. and Meyer B.S. (2014) Physics Review C 89, 025807.
[10] Rauscher T. et al. (2022) The Astrophysical Journal 576, 323.
[11] Walls L.S. et al. (2025) 56th Lunar and Planetary Science Conference, Abstract #2708.
[12] Pignatari M. et al. (2013) The Astrophysical Journal Letters 767, L22.

Speaker: Nan Liu (Boston University)

28 Correlated heavy isotope signatures in presolar SiC

The isotopic compositions of Zr, Mo, Ru, and Ba in presolar SiC have much to tell us about nucleosynthesis in stars, particularly asymptotic giant branch (AGB) stars, the likely sources of mainstream as well as types Y and Z presolar SiC grains. We highlight here two examples from recent simultaneous measurements on multiple elements in single presolar grains. (1) From their Mo and Ru isotopic compositions, the mainstream, Y-, and Z-type SiC grains from the Murchison meteorite have remarkably constant and solar-like ratios of r- to p-process isotopes, implying that their parental AGB stars had near-solar initial isotopic compositions. (2) Zr, Mo, and Ba isotopes were measured in over 80 presolar SiC grains from the Aguas Zarcas meteorite over the past two weeks. We will summarize recent data and their implications for nucleosynthesis and mixing in AGB stars.

Speaker: Prof. Andrew Davis (University of Chicago)

29 Effects of Metallicity on Graphite, TiC, and SiC Condensation in Carbon Stars

Speaker: Gabrielle Adams (Washington University in St. Louis)

30 Origin of Rare Isotopes in Presolar Grains as the Probe of Neutrino Mass Hierarchy and Supernova Nucleosynthesis

Here we present our study on isotopic ratios of several typical neutrino-process nuclides in core-collapse supernova. We find that the measurement of isotopic ratios like 11B/10B with 138La/139La or 6Li/7Li can constrain neutrino mass hierarchy, providing new probes for understanding CCSN nucleosynthesis. Additionally, we show that the correlation between 138La/139La and 50Ti/48Ti in calcium-aluminum inclusions (CAIs) can be quantitatively explained by CCSN models with weak s-process, suggesting that CCSNe contributed to the early solar system's material. Our results indicate that isotopic abundance analysis in CAIs and presolar grains is crucial for understanding the origins of these rare isotopes.

[1] Y. Luo, T. Kajino, T. Hayakawa and Tsuyoshi Iizuka (2025), to be published.
[2] X. Yao, T. Kajino, Y. Luo, et al., Astrophys. J. 980 (2025), 247 (21pp).
[3] X. Yao, Y. Luo, T. Kajino, et al., Chinese Phys. C (2025), submitted.

Speaker: Dr Yudong Luo (Peking University)

Stellar Evolution I – Hydrostatic Evolution, AGBs, Massive Stars, S-Process

31 Nucleosynthesis in Low- and Intermediate-Mass Stars

Speaker: A Choplin

32 FLASH Session IV

13:00 Lunch Break

Stellar Evolution I – Hydrostatic Evolution, AGBs, Massive Stars, S-Process

33 Nucleosynthesis and wind yields of Very Massive Stars

The most massive stars provide an essential source of recycled material for young clusters and galaxies. While very massive stars (VMS, M > 100M$_{\odot}$) are relatively rare compared to O stars, they lose disproportionately large amounts of mass already from the onset of core H-burning. In this talk, I will discuss the impact of stellar wind yields from VMS, calculated for a wide range of masses (50−500M$_{\odot}$). I will present chemical yields for metallicities ranging from Z$_{\odot}$ down to 1% solar metallicity, using the MESA stellar evolution code with updated mass-loss prescriptions. We find that for VMS at solar metallicity, 95% of the total wind yields are produced already on the main sequence, while only ∼ 5% is supplied by the post-main sequence. With optically-thick winds, these VMS eject significant quantities of H-burning products such as $^{14}$N, $^{20}$Ne, $^{23}$Na, and $^{26}$Al. At low metallicity, VMS can also produce Na-enriched and O-depleted material which is key for the observed anti-correlations in globular clusters.

Speaker: Erin Higgins (Queen's University Belfast)

34 The Role of Carbon-Oxygen Shell Interactions in the Nucleosynthesis and Final Fate of Massive Stars

Carbon-oxygen (C-O) shell interactions in the late evolutionary stages of massive stars play a crucial role in determining their final fate and have a significant impact on the pre-supernova and explosive nucleosynthesis. In this talk, I will explore the complex dynamics within C-O shells, and how these interactions drive the production of intermediate and heavy elements. In particular I will address how stellar models experiencing a C-O shell merger can efficiently produce odd-Z nuclei such as P, Cl, K, and Sc, and the radioactive species $\rm ^{44}Ti$. I will then outline how the occurrence of such a merger would favour the successful explosion of a massive star, leading to the enrichment of the interstellar medium with peculiar nucleosynthetic signature.

Speaker: Lorenzo Roberti (Laboratori Nazionali del Sud)

35 Comparing the Elemental Yields from Low-Mass Single and Binary Star Populations

Asymptotic giant branch (AGB) stars are evolved stars born with a low mass of about 1-8M⊙, depending on their metallicity. These stars are vital to the chemical enrichment of the universe as they synthesise and eject significant amounts of carbon, nitrogen, fluorine, and about half of the material heavier than iron through the slow neutron capture process. However, one aspect often overlooked when studying the chemical contribution of low-mass stars is the influence of binary evolution. About half of low-mass stars are observed to have a stellar companion, and binary mechanisms such as mass transfer and common envelopes can alter or prevent stellar evolution onto the AGB. We use binary population synthesis to model stellar populations of single and binary low-mass stars at metallicities Z = 0.015, 0.0028, and 0.0001 to explore how binary evolution affects the formation rates of AGB stars and the consequences on the elemental yields. Overall, we find that binary evolution reduces the number of AGB stars by about 30%, limiting the ability of low-mass stars to contribute to the chemical enrichment of the universe.

Speaker: Zara Osborn (Monash University)

36 Common Envelope Nucleosynthesis: investigation into how nucleosynthesis can vary across different neutron star common envelope binaries

In 2017 the first neutron star merger was observed at LIGO, and for a neutron star binary system to merge within a hubble time the progenitor system must undergo a common envelope phase to dissipate the orbital energy and bring the two compact masses closer together [1]. During the common envelope phase the compact neutron star orbits within the envelope of the companion star and accretes material from the companion onto the neutron star surface. During this accretion a disk will form around the neutron star in which material is heated to extreme temperatures, providing an area for high energy nucleosynthesis to occur. A fraction of the accreted material is then mixed back into the shared envelope, which is then ejected into the interstellar medium at the end of the common envelope phase. An initial investigation into the ejection mechanism when material is in free fall towards the neutron star was conducted by Keegans et al. [2019] [2] and showed evidence of proton rich nucleosynthesis occuring during accretion. The work presented in this talk will show how the nucleosynthesis varies when using more realistic trajectories, which include the effects of angular momentum. I will also present results from a range of different neutron star common envelope binaries in which the accretion rate, neutron star mass, companion mass, and companion age are varied.

[1] Dominik, M., Belczynski, K., Fryer, C., Holz, D.E., Berti, E., Bulik, T., Mandel, I. and O'shaughnessy, R., 2012. Double compact objects. I. The significance of the common envelope on merger rates. The Astrophysical Journal, 759(1), p.52.

[2] Keegans, J., Fryer, C.L., Jones, S.W., Côté, B., Belczynski, K., Herwig, F., Pignatari, M., Laird, A.M. and Diget, C.A., 2019. Nucleosynthetic yields from neutron stars accreting in binary common envelopes. Monthly Notices of the Royal Astronomical Society, 485(1), pp.620-639.

Speaker: Alexander Hall-Smith (the University of York)

37 FLASH Session V

16:00 Coffee Break

Nuclear Theory

38 Nuclear Theory Challenges for Nuclear Astrophysics

Speaker: Stephane Goriely (Université Libre de Bruxelles)

NIC25_Goriely.pdf

39 Bayesian Uncertainty Quantification of Alpha Elastic Scattering to Constrain the $\alpha$ Optical Model

Accurate predictions of $\alpha$-induced reactions on medium mass nuclei are critically reliant on the alpha optical model potential ($\alpha$OMP). At the energies relevant to explosive nucleosynthesis, the behavior of the $\alpha$OMP is poorly constrained by existing data, leading to orders of magnitude variation in thermonuclear reaction rates undermining the predictive accuracy of stellar models. To improve this situation, targeted experiments are needed not only to measure astrophysically relevant reactions, but to improve $\alpha$OMP phenomenology in general. In this talk I will present results from a recent $^{86}$Sr$(\alpha, \alpha)$ experiment performed at the Triangle Universities Nuclear Laboratory. Employing a first of its kind Bayesian analysis, we carried out an extensive investigation of the constraints that can be placed on the $\alpha$OMP from a single elastic scattering experiment. Our results demonstrate that despite ambiguities in potential parameters and non-unique energy dependencies, the low-energy cross-section can be predicted with a precision of $50 \%$.

Speaker: Caleb Marshall (University of North Carolina at Chapel Hill, Triangle Universities Nuclear Laboratory)

40 FLASH Session VI

Poster Session

Wednesday 18 June

Nuclear Theory: Microscopic Description of β-Decay Rates of R-Process Nuclei

Convener: Diana Alvear Terrero (Technische Universität Darmstadt)

41 Microscopic description of $\beta$-decay rates of r-process nuclei

The r-process nucleosynthesis produces roughly half of the heavy elements found in nature. Among its nuclear physics inputs, the $\beta$-decay half-lives of extremely neutron-rich nuclei is a key ingredient. Since experimental data in this region is limited, we need theoretical predictions that are globally applicable. Here we present improvements to the existing self-consistent RHB+RQRPA approach including Gamow-Teller and first forbidden transitions. We discuss the $\beta$-decay half-lives, their sensitivity to the isoscalar pairing strength and the predictions of $\beta$-delayed neutron emission probabilities benchmarked to experimental data.

Speaker: Diana Alvear Terrero (Technische Universität Darmstadt)

Big-Bang Nucleosynthesis and Early Universe

42 Big Bang Nucleosynthesis and Early Universe

Speaker: Brian D. Fields

43 Neutron induced reactions for BBN: the Trojan Horse approach

Nuclear reactions induced by neutrons play a key role in several astrophysical scenario like primordial nucleosynthesis, s and r process and so on. From an experimental point of view, their reaction cross sections and reaction rates at astrophysically relevant temperatures are usually a hard task to be measured directly. Nevertheless big efforts in the last decades have led to a better understanding of their role in the different nucleosynthetic networks. In this work we will review the possibility of application of the Trojan Horse Method to extract the cross section at astrophysical energies for neutron induced reactions, examining validity tests as well as different applications. Moreover a detailed study of the $^3$He(n,p)$^3$H reaction off the $^2$H($^3$He,pt)H three--body process will be discussed. The experiment was performed using the $^3$He beam, delivered at a total kinetic energy of 9 MeV by the Tandem at the Physics and Astronomy Department of the University of Notre Dame. Data extracted from the present measurement are compared with other published sets available in literature. the reaction rate will be calculated and the astrophysical applications will also be discussed in details for the case of the Big Bang Nucleosynthesis.

Speaker: Rosario Gianluca Pizzone (University of Catania and Istituto Nazionale di Fisica Nucleare)

44 Ending the second cosmological Li problem

Lithium is the heaviest element produced during Big Bang nucleosynthesis. The amount produced can be predicted through the cosmic microwave background and measured through old metal-poor stars. Li has two stable isotopes, with Li-7 being more abundant than Li-6. In particular, the detection of Li-6 in old metal-poor halo stars contradicts the Big Bang nucleosynthesis prediction by 5 orders of magnitude; this disagreement is known as the second cosmological lithium problem. We investigate the detections of Li-6 within three stars through the use of ESPRESSO@VLT observations and state-of-the-art synthetic spectra. We do not detect Li-6 in any star, indicating that there is no second cosmological lithium problem. This is consistent with Galactic modelling assuming Li destruction in old metal-poor stars.

Speaker: Ella Wang (Stockholm University)

Stellar Evolution II – Supernovae, Kilonovae, Mergers, R- and P-Process

45 Nucleosynthesis in core-collapse supernovae

Core-collapse supernovae play a central role in the chemical evolution of the universe. They eject the elements synthesised during the life of massive stars and produce heavy elements. There have been major advances in the hydrodynamical simulations and in the microphysics included (neutrinos and high density equation of state), in galactic chemical evolution models, and in observations of old stars in our galaxy and in dwarf galaxies. This talk will report on recent developments to understand these extreme environments and their nucleosynthesis beyond iron group nuclei, which depends on the explosion mechanism: neutrino-driven or magneto-rotational supernovae. Moreover, the combination of nucleosynthesis calculations and observations can constrain the astrophysics conditions, once the nuclear physics uncertainties are reduced.

Speaker: Almudena Arcones (TU Darmstadt & GSI)

Arcones_NIC.pdf

46 Neutron Star Mergers and Kilonovae: r-Process and Gravitational Waves

Neutron star mergers are the prime example for multi-messenger events with the potential to address many open questions with regards to nucleosynthesis of heavy elements and the properties of high-density matter. This concerns for instance the composition of the outflows and to which extent they resemble the solar abundance pattern. Also, the existence of non-nucleonic degrees of freedom in the cores of neutron stars is yet unclear and may be elucidated by detections of gravitational waves and kilonovae. We will present some recent developments combining the insights from the kilonova emission and the gravitational radiation of GW170817. For instance, a thorough analysis suggests that the merger remnant in GW170817 was not very long-lived and that relatively little amounts of helium were produced in the outflow from this event. The early black-hole formation places an upper bound on the maximum mass of neutron stars and on the radii of neutron stars.

Speaker: Mr Andreas Bauswein (GSI Darmstadt)

10:45 Brunch

12:00 Excursions

Thursday 19 June

Stellar Evolution II – Supernovae, Kilonovae, Mergers, R- and P-Process

47 Trans-Fe elements from Type Ia Supernovae

A Type Ia supernova (SNIa) marks the catastrophic explosion of a white dwarf in a binary system. These events play a crucial role in galactic chemical evolution and serve as pivotal standardizable candles for measuring cosmic distances, underpinning the discovery of the Universe's accelerated expansion. However, the progenitors of SNIa remain uncertain, introducing challenges to their use in cosmology and nucleosynthesis predictions.
In this work, we present a grid of five models detailing the evolution and nucleosynthesis of slowly merging carbon-oxygen white dwarfs approaching the Chandrasekhar mass. These models test a variety of physics input settings, including accretion rates, nuclear reaction rates, convection parameters, and the composition of the accreted material. During the merger process, as the mass of the primary white dwarf approaches the Chandrasekhar limit, carbon burning is initiated first on the surface before eventually igniting explosively at the center. As a consequence, the $^{22}$Ne($\alpha$,n)$^{25}$Mg reaction activates in the outer layers of all models, producing a weak $s$-process-like abundance pattern peaking at Kr, which is overproduced by more than a factor of $\sim$1000 compared to solar. The trans-Fe elements-enriched outer layer mass varies from 0.04~M$_{\odot}$ to 0.11~M$_{\odot}$, depending on the accretion rate. Additionally, up to $\sim$6$\times$10$^{-6}$M$_{\odot}$ of $^{60}$Fe are produced in the same outer layers. Our explosion simulations of these progenitor models eject significant amount of first-peak elements (e.g., Kr, Sr) and light $p$-nuclei (e.g., $^{74}$Se).
In a previous theoretical study, we found that a similar nucleosynthesis process during the progenitor phase may also occur on the surface of near-Chandrasekhar white dwarfs formed through the accretion of H-rich material via the single-degenerate scenario. Therefore, these results suggest trans-Fe enrichment might be a hallmark of near-Chandrasekhar SNIa ejecta, regardless of the specific progenitor channel, and could provide a new spectral signature distinguishing them from sub-Chandrasekhar explosions.

Speaker: Umberto Battino (University of Naples "Federico II")

48 Probing Pair-Instability Supernovae via 56Ni Decay Signatures

Pair-instability supernovae (PISNe) are theorized thermonuclear explosions of extremely massive stars, predicted to occur when the helium core mass exceeds ∼65M⊙. The large amounts of radioactive 56 Ni synthesized in such events (∼60M⊙ in extreme cases) can power extraordinarily luminous optical light curves, but to date no supernova has been definitively confirmed as a PISN. Direct detections of high-energy emission from the decay chain 56Ni → 56Co → 56Fe would provide unambiguous evidence for these explosions. In this work, we investigate the detectability of gamma-ray and hard X-ray signals from a suite of PISN models and compare them with the capabilities of current and near-future observatories. We find that for a PISN model with a helium core mass of MHe =130M⊙​, the dominant 56Co-decay lines at 847 and 1238 keV would be detectable out to distances of about 300 Mpc by upcoming gamma-ray missions with improved sensitivity.　Furthermore, it is known that the 12C(a, g)16O nuclear reaction has a significant effect on PISN nucleosynthesis. We will also discuss observational constraints on this nuclear reaction using the gamma-ray emission of this model. These results strongly motivate targeted high-energy campaigns to confirm—or rule out—the long-sought phenomenon of PISNe.

Speaker: RYO SAWADA (The Institute for Cosmic Ray Research, UT)

49 3D Simulations of White Dwarf-Main Sequence Star Collisions

Stellar collisions have garnered renewed attention for their role in the formation of peculiar objects, such as blue stragglers, and their potential to explain explosive transients with atypical observational and spectroscopic signatures. Among these, white dwarf-main sequence (WD-MS) collisions are particularly intriguing due to the diverse evolutionary pathways they can produce—ranging from peculiar red giants to novae or sub-Chandrasekhar supernovae. In this talk, we present 3D smoothed particle hydrodynamics (SPH) simulations of WD-MS collisions, exploring a range of stellar mass ratios, velocities and impact parameters. We discuss the overall dynamics, energetics, gas morphology and mass loss, and in addition, using a 34-isotope nuclear network, we estimate the nucleosynthesis products generated during these collisions. Our models suggest that at early times the ejecta have a bipolar structure and, along with the stellar remnant, may be enriched in isotopes such as $^{13}$C, $^{15}$N, and $^{17}$O. In the case of near head-on collisions, the ejecta may also show an overabundance of $^{7}$Li relative to solar values.

Speaker: Christian J. T. van der Merwe (University of Cape Town, South Africa, and 2South African Astronomical Observatory,)

50 Neutrino-Mass Hierarchy and The Roles of Radioactive Nuclear Reactions in Explosive Nucleosynthesis of Supernovae, Collapsars and Mergers

The detection of gravitational waves from the binary neutron star merger GW170817 and supernova (SN) neutrinos from SN1987A opened a new era of multi-messenger astronomy and astrophysics, and we are able to understand the cosmic chemical evolution with these events to seek for the origin and evolution of atomic nuclei. A keen scientific objective is to understand how the strong, electromagnetic and weak interactions play the role in SN explosion dynamics and nucleosynthesis. Firstly, we will propose a new astrophysical method of supernova nucleosynthesis to constrain still unknown neutrino mass hierarchy [1]. The flavor conversion effects due to the collective quantum effect as well as MSW effect are found to play the critical roles in neutrino-process nucleosynthesis at high density. We also propose that the isotopic ratios among Lithium, Boron, Lantanum, etc. in in SN presolar-grains provide a clear signature of mass hierarchy dependence [1]. Secondly, we will discuss the roles of radioactive ion-beam (RIB) reactions, where we find that C11(a,p)N14 and several others strongly affect explosive nucleosynthesis of Lithium and Boron isotopes [2]. We have recently found that the i- and s-processes could occur in the r-process site of collapsar nucleosynthesis [3], and we make a list of important unmeasured RIB reactions on light-to-heavy mass nuclei [4]. Finally, we will clarify how the different candidate astrophysical sites for the heavy element production, i.e. magneto-hydrodynamic-jet SNe, collapsars, and binary neutron-star mergers, have contributed to the enrichment of heavy elements in cosmic evolution [5].

[1] X. Yao, T. Kajino, Y. Luo, et al., Astrophys. J. 980 (2025), 247(21pp).
[2] X. Yao, Y. Luo, T. Kajino, et al., Chinese Physics C (2025), to be published.
[3] Z. He, T. Kajino, M. Kusakabe, et al., Astrophys. J. Lett. 966 (2024), L37.
[4] Z. He, T. Kajino, Y. Luo, et al., (2025), to be published.
[5] Y. Yamazaki, Z. He, T. Kajino, et al., Astrophys. J. 933 (2022), 112.

Speaker: Toshitaka Kajino (Beihang University, University of Tokyo, National Astronomical Observatory of Japan)

Neutrinos

51 Collective neutrino oscillations and the heavy-element nucleosynthesis in supernova

In high energy astrophysical processes involving compact objects, such as core-collapse supernovae or neutron star mergers, neutrinos are likely to play an important role in the synthesis of nuclides. Neutrinos in these environments can experience collective flavor oscillations driven by neutrino-neutrino coherent forward scattering. Recently, there has been interest in exploring potential beyond-the-mean-field effects in the collective oscillations of neutrinos. Here, we seek to explore possible implications of these effects for the heavy-element nucleosynthesis yields in supernova environments with different astrophysical conditions and neutrino inputs. We find that collective oscillations can impact the operation of the νp-process and r-process nucleosynthesis in supernovae. The potential impact is particularly strong in high-entropy, proton-rich conditions, where we find that neutrino interactions can nudge an initial νp process neutron rich, resulting in a unique combination of proton-rich low-mass nuclei as well as neutron-rich high-mass nuclei. We describe this neutrino-induced neutron capture process as the "νi process". In addition, nontrivial quantum correlations among neutrinos, if present, could lead to distinctly different nucleosynthesis results compared to the corresponding mean-field treatments, by virtue of modifying the evolution of the relevant one-body observables.

Speaker: Xilu Wang (Institute of High Energy Physics, Chinese Academy of Sciences)

52 Neutrino Oscillations in Post-Merger Disks

The remnant black-hole accretion disk system that results from binary neutron star mergers has proven to be a promising site for the synthesis of the heaviest elements through the rapid neutron capture process (r-process). One of the key quantities determining the extent to which these sites are capable of producing a full r-process pattern is the neutron richness of the ejecta, which is heavily influenced by neutrino interactions in the disk during its evolution. We present results from a 3D general-relativistic magnetohydrodynamics disk simulations with Monte Carlo neutrino transport, showing the effect neutrino oscillations have on the conditions for r-process nucleosynthesis in the disk.

Speaker: Kelsey Lund (UC Berkeley)

10:00 Coffee Break

High-Density Matter and EOS of Neutron Stars

53 The equation of state of neutron-star matter

Neutron stars are unique laboratories to probe matter in extreme conditions that cannot be currently reproduced on Earth. The determination of their equation of state (EoS) is a challenge, but it is particularly important since it allows to relate different global neutron-star properties and to link the prediction of astrophysical observables to microphysical properties of dense matter.

In this presentation, I will give a brief introduction on the dense-matter EoS, and specifically on the EoS for neutron stars. Various constraints coming from both nuclear physics and astrophysics will be discussed. The prediction for the dense-matter EoS and neutron-star observables obtained with a large variety of EoSs will be presented in connection with (multi-messenger) observations.

Speaker: Anthea Francesca Fantina (Grand Accélérateur National d'Ions Lourds (GANIL))

54 New Constraints on the Neutron Star Equation of State

The calculation of the equation of state (EOS) of nuclear matter beyond saturation density (n_sat) remains an open research problem. However, observations of neutron stars have proven crucial to the study of matter at these higher densities, especially since the detection of gravitational waves from binary neutron star mergers by LIGO and the determination of simultaneous mass-radius contours from pulse profile modeling by NICER have significantly constrained the EOS beyond n_sat. In addition, recent advances in the calculation of nucleon interactions from chiral effective field theory (EFT) determine the EOS up to 1-2 n_sat, providing an independent constraint. In this talk I will discuss our most updated EOS constraints from recent chiral EFT calculations and NICER data, including the pulsar J0437-4715, within an open-source Bayesian framework.

Speaker: Melissa Mendes (TU Darmstadt)

55 Core-collapse supernova simulations based on the new HWS EOS

The equation of state (EOS) of dense matter plays a key role in the evolution of the proto-neutron star (PNS) and the dynamics of the core-collapse supernova (CCSN) explosion. We present new EOS tables based on the model of Huth et al (2021), that consider constraints from nuclear theory calculations, experiments, and astrophysical observations. In this study, we systematically vary nuclear matter properties and study their impact on CCSN simulations. We show the effects of considering the new, density-dependent, effective mass functional, which governs the thermal nucleonic part of the EOS, that has a big impact on the PNS contraction and therefore on the CCSN explosion. In addition, we investigate the impact of cold nuclear matter properties, within their constraints, on CCSN simulations.

Speaker: Gerard Navó (Universitat de València)

Stellar Evolution III – Novae and XRBs

56 Nucleosynthesis in Explosive H-Burning Scenarios

Speakers: Hendrik Schatz, Hendrik Schatz

57 H-triggered X-ray Bursts on Slowly Accreting Neutron Stars

Many observed neutron stars are in binaries and accrete hydrogen-rich material from low-mass companions. The accumulating matter eventually triggers a thermonuclear runaway that results in an X-ray burst lasting 10–100s with a recurrence time of hours to days. Almost all observed thermonuclear X-ray bursts are thought to be triggered by the thermally unstable triple-alpha process, as most observed bursters are sufficiently hot that hydrogen burning is via the beta-limited, thermally stable hot CNO cycle. Recently, two faint bursts were detected from SAX J1808.4-3658 that were plausibly triggered by thermally unstable CNO burning. If confirmed, this would be the first observation of unstable H burning on an accreting neutron star. Using MESA, a stellar evolution code, we explore the unstable ignition of H on a slowly accreting, cool neutron star over a range of metallicities (0.01< Z< 0.30). Analogous to unstable H ignition in classical novae, we find that the CNO abundance at the base of the accreted layer must be enhanced in order to launch convection and produce a sharp rise and an observable burst. Following this initial burst, our models settle into a long phase of thermally stable, hot CNO burning that produces an extended tail. This tail is also seen in the observed bursts. The tail energetics and duration depend on the CNO abundance in the accreted matter, and thus open a new probe into mixing in the neutron star envelope.

Speaker: Sierra Casten (Michigan State University)

58 Experimental study of the $^{15}$O($\alpha$,$\gamma$)$^{19}$Ne reaction for understanding type I X-ray bursts

The $^{15}$O($\alpha$,$\gamma$)$^{19}$Ne reaction is a key breakout route from the hot CNO cycle in explosive environments such as in type I X-ray bursts. Determining an accurate cross section for the relevant resonant states is critical for a better understanding of the X-ray burst energy production and light-curves, and of the subsequent nucleosynthesis through the ap- and rp-processes.

The relevant $^{19}$Ne states for temperatures up to 1 GK were populated using an indirect $^{15}$O($^{7}$Li,t)$^{19}$Ne alpha transfer reaction measurement in inverse kinematics. The experiment used an intense radioactive $^{15}$O beam produced by SPIRAL1 at GANIL and the state-of-the art detection system VAMOS + MUGAST + AGATA, for the detection of the heavy residues, the light charged particles and the de-exciting $\gamma$-rays, respectively. This allowed to reach an unprecedented selectivity for detecting triple coincidences of all final state particles in this reaction.

In this presentation, we will outline the experimental set-up and analysis, providing results for the strongest populated resonances in $^{19}$Ne. In particular, our result with reduced uncertainty for the alpha width of the critical 4.033 MeV excited state will be presented. New astrophysical $^{15}$O($\alpha$,$\gamma$)$^{19}$Ne reaction rates will be presented and the impact on X-ray burst light-curves will be discussed.

Speaker: Nicolas de Séréville

59 Weak rp-process nucleosynthesis in low-metallicity novae explosions

Classical novae are stellar thermonuclear explosions that occur when a white dwarf accretes material from a companion star. In the early Galactic history, and still today in metal-poor environments, these explosions likely proceeded differently due to the accretion of sub-solar metallicity material. It has been suggested that such low-metallicity novae produced distinct abundance patterns compared to their more recent counterparts [1]. In particular, nuclear processes in low-metallicity novae extend up to the Cu-Zn region, resembling a weak rp-process, whereas classical novae typically terminate around Ca. In this talk, we investigate nucleosynthesis in this scenario and assess the impact of nuclear physics uncertainties on the final abundance pattern. Using a Monte Carlo approach [2,3], we varied all relevant reaction rates within their uncertainties to identify key nuclear processes influencing the production of intermediate-mass nuclei [4]. Our results highlight specific reactions whose uncertainties significantly affect nucleosynthesis under low-metallicity-nova conditions [5]. These reactions require experimental measurements at both stable and radioactive beam facilities to improve their rate precision. To begin addressing these uncertainties, we discuss recent indirect (³He,d) transfer measurements conducted at the Triangle Universities Nuclear Laboratory (TUNL) using the Enge split-pole spectrograph. These measurements provide crucial constraints on (p,γ) reaction rates, improving our understanding of nucleosynthesis in low-metallicity novae.

• This work is supported by U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Award Number DE-SC0017799 and Contract Nos. DE-FG02-97ER41033 and DE-FG02-97ER41042.

References
[1] J. José et al., Astrophys. J 622, L103 (2007).
[2] A.L. Sallaska et al., Astrophys. J Suppl. Ser. 207, 18 (2013).
[3] R. Longland et al., Nucl. Phys. A 841, 1 (2010).
[4] C. Iliadis and A. Coc, Astrophys. J 901, 127 (2020).
[5] A. Psaltis et al. (in preparation).

Speaker: Thanassis Psaltis (TUNL)

13:00 Lunch Break

Galactic Chemical Evolution

60 Recent Advances in Galactic Chemical Evolution

Speaker: G Cescutti

61 Galactic chemical Evolution with short lived radioactive isotopes

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].

We further provide predictions for future gamma-ray detection instruments.

References:
[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, A9

Speaker: Benjamin Wehmeyer (University of Wroclaw)

62 26Al: how to model a short-lived radioactive isotope - from a 1D to a 2D approach

$^{26}$Al is a short-lived radioactive nucleus ($\tau_{1/2}\,\sim$1 Myr) that can be used as a tracer of active star formation regions. In the past decades, observational data were collected in the Milky Way by $\gamma$-satellites as COMPTEL and INTEGRAL and I will show how we can reproduce them via chemical evolution models. The starting point is adopting a 1D chemical evolution model of the Milky Way. By making assumptions regarding the star formation rate (SFR), the initial mass function (IMF) and the stellar yields this approach puts new constraints on the production of $^{26}$Al by nova systems. I further investigated this topic adopting a 2D chemical evolution model to account for the dishomogeneous distribution of $^{26}$Al in our Galaxy arising from the spiral arm pattern observed and by exploring different environments, such as the Large Magellanic Cloud, in order to make predictions for COSI, the new $\gamma$-ray satellite to be launched in 2027.

Speaker: Arianna Vasini (Università dell'Insubria - Dipartimento di Scienza e Alta Tecnologia)

New Facilities and Techniques

63 Nuclear Astrophysics at the Bellotti Facility, Laboratori Nazionali del Gran Sasso

The Bellotti Ion Beam Facility (IBF) [1] is located in the deep underground site of INFN-Laboratori del Gran Sasso (LNGS), Italy. The facility is named in honor of Enrico Bellotti, the first director of the Laboratori Nazionali del Gran Sasso (LNGS), Italy, who initiated the first installation of an underground accelerator for the study of nuclear reactions of astrophysical interest, following a proposal by C. Rolfs and G. Fiorentini. The facility offers unique opportunities for experiments with intense proton, alpha, and carbon beams in an environment where the cosmic muon flux is reduced by six orders of magnitude compared to the Earth's surface. The primary instrument at the facility is a 3.5 MV Singletron accelerator supplied by High Voltage Engineering Europa in specifications developed at LNGS [2]. The Italian Ministry of Education, University and Research funded the machine on a proposal originated by the LUNA Collaboration.

Since its inauguration in October 2023, Bellotti IBF is being operated as a scientific user facility, available to external users, with the technical management assigned to the Accelerator Service of LNGS. During the first years of operation, the Bellotti IBF has provided ion beams for nuclear astrophysics experiments, whilst concomitant measurements were undertaken for the purpose of precise ion beam energy calibration.

This presentation will provide a comprehensive overview of the characteristics at Bellotti IBF and the related perspectives in the field of Nuclear Astrophysics.

[1] The deep underground Bellotti Ion Beam Facility—status and perspectives, M. Junker, G. Imbriani, A. Best, A. Boeltzig, A. Compagnucci, A. Di Leva, F. Ferraro, D. Rapagnani, V. Rigato (2023), The deep underground Bellotti Ion Beam Facility—status and perspectives. Front. Phys. 11:1291113. DOI: 10.3389/fphy.2023.1291113

[2] A High Intensity, High Stability 3.5 MV Singletron™ accelerator, A. Sen , G. Domínguez-Cañizares, N.C. Podaru, .J.W. Mous, M. Junker , G. Imbriani, V. Rigato; Nuclear Instruments and Methods in Physics Research Section B 2019; DOI: 10.1016/j.nimb.2018.09.016

Speaker: Matthias Junker (INFN - Laboratori Nazionali del Gran Sasso)

64 Nuclear Astrophysics at JUNA

Speaker: Weiping Liu (Southern university of science and technology)

16:15 Coffee Break

New Facilities and Techniques

65 Nuclear astrophysics activities at CENS

The IBS Center for Exotic Nuclear Studies (CENS) in Korea has a dedicated nuclear astrophysics group conducting experiments with both radioactive isotope (RI) and stable beams. The low-energy accelerator of the RI beam facility RAON is now in operation. The experimental facility KoBRA will utilize 20–30 MeV/u beams from the low-energy accelerator and is expected to conduct nuclear astrophysics experiments during the early phase of RAON. We are actively developing several major instruments such as active target TPC detectors, silicon detector array, and cryogenic gas target system. Some of our research focus on key reactions related to the HCNO cycle and the rp-process such as 14O(a,p)17F, which we performed a direct measurement using an active target TPC at the CRIB facility. We also plan to measure the 34Ar(a,p)37K reaction. Current research activities, experimental development, and future plans for nuclear astrophysics experiments at RAON in Korea and other RI beam facilities will be presented

Speaker: Kevin Hahn (Institute for Basic Science)

66 Direct measurement of neutron capture on radioactive isotopes at CERN n_TOF

Neutron-capture reactions drive the formation of elements heavier than iron, occurring through both the slow (s-) process in low-mass AGB and massive stars, and the rapid (r-) process in explosive stellar environments. In the s-process mechanism, unstable branching isotopes serve as unique tracers, offering crucial insights into the physical conditions and intricate details of stellar nucleosynthesis. Neutron-capture measurements on radioactive isotopes, in combination with stellar spectroscopy and isotopic analyses of primitive meteorites, can help to better understand the role of stellar mass, rotation or metallicity and to refine further our understanding of galactic chemical evolution. However, from an experimental standpoint, determining neutron-capture cross-sections of radioactive isotopes remains a challenge. The primary obstacles include the production of high-quality radioactive samples and the need for highly sensitive and selective detection techniques to isolate the reaction channel of interest.
This contribution presents a comprehensive overview of the key s-process branching isotopes measured at the CERN neutron Time-of-Flight (n_TOF) facility over the past two decades. The astrophysical significance of these studies will be highlighted and it will be shown how upgrades in the neutron-beam facility and state-of-the-art detector developments have led to a stunning progress on the measurement of such radioactive nuclides. Despite these breakthroughs, significant limitations still persist, particularly concerning isotopes with short half-lives (smaller than a few years), restricted neutron energy ranges (beyond a few keV), and statistical uncertainties exceeding 10%. In this respect, CERN n_TOF has ambitious plans to push the boundaries of neutron-capture measurements, along with innovative approaches to overcoming current limitations in sample production and isotopic half-life constraints. These advancements hold the potential to unlock new frontiers in our understanding of stellar nucleosynthesis and may enable access to direct measurements of neutron-capture cross sections on other nucleosynthesis mechanisms, such as the intermediate (i-) process and the r-process.

Speaker: Cesar Domingo Pardo (IFIC (CSIC-UV))

67 Nuclear Astrophysics at FRIB

Speaker: Chris Wrede

68 Investigating explosive nucleosynthesis through measurements of ($\alpha$,n) and (p,n) reactions using SECAR

Heavy element synthesis in explosive stellar environments, such as core-collapse supernovae, is influenced by key nuclear reactions involving unstable nuclei. In neutron-rich conditions, the $\alpha$-process, which involves a sequence of ($\alpha$,xn) reactions, plays a significant part in nucleosynthesis, whereas (p,n) reactions influence element formation during explosive silicon burning and the $\nu$p-process. However, experimental data on these reactions remain scarce, introducing significant uncertainties in astrophysical models.

Although SECAR (SEparator for CApture Reactions) is primarily designed for capture reactions, it can be utilized to measure the heavy recoils from other reactions. A new technique has been developed for direct measurements of both ($\alpha$,n) and (p,n) reactions in inverse kinematics with SECAR. The development of machine learning-assisted ion-optics rendered the study of (p,n) reactions using a separator feasible. The $^{58}$Fe(p,n) reaction measurement served as a validation of the method. Additionally, SECAR’s capabilities have been extended to include ($\alpha$,n) reaction measurements. The first case studied was the $^{86}$Kr($\alpha$,n) reaction, which influences $\alpha$-process nucleosynthesis and metal-poor star abundances.

In this contribution I will present the recent ($\alpha$,n) and (p,n) reaction measurements with SECAR, highlighting their astrophysical significance and the experimental advancements that enable these studies. These results pave the way for future direct measurements of reaction rates on short-lived nuclei, which will significantly improve our understanding of heavy-element nucleosynthesis.

Speaker: Pelagia Tsintari (Facility for Rare Isotope Beams, Michigan State University)

69 Nuclear Astrophysics with Stored Highly Charged Radioactive Ions

Storage of freshly produced secondary particles in a storage ring is a straightforward way to achieve the most efficient use of the rare species as it allows for using the same secondary ion multiple times. Employing storage rings for precision physics experiments with highly-charged ions (HCI) at the intersection of atomic, nuclear, plasma and astrophysics is a rapidly developing field of research. The number of physics cases is enormous. In the focus of this presentation will be the most recent results obtained at the Experimental Storage Ring ESR of GSI in Darmstadt and the Experimental Cooler-Storage Ring CSRe of IMP in Lanzhou.
Both the ESR and CSRe rings are coupled to in-flight fragment separators and are employed for precision mass spectrometry of short-lived rare nuclei. At CSRe, the enabled measurement of the velocity of every stored particle—in addition to its revolution frequency—has boosted the sensitivity and precision of mass measurements, which lead to accurate determination of the remaining masses constraining matter flow though 64Ge waiting point in the rp-process nucleosynthesis.
The ESR is presently the only instrument dedicatedly utilized for precision studies of decays of HCIs. Radioactive decays of HCIs can be very different as known in neutral atoms. Some decay channels can be blocked while new ones can become open. Such decays reflect atom-nucleus interactions and are relevant for atomic physics and nuclear structure as well as for nucleosynthesis in stellar objects. After several decades of tedious preparatory work, the bound state beta decay of 205Tl could be measured. This quantity allowed us to address the history of the early Solar system and to provide constraints on the feasibility of geochemical Solar pp-neutrino detection.
Furthermore, both the CSRe and the ESR are utilized for nuclear reaction studies, where the beam cooling combined with internal ultra-thin ultra-pure windowless gas targets enables high angular and energy resolution. In the recent years, a series of proton-induced reactions were addressed in the ESR, where, thanks to new background elimination techniques, in addition to (p,g) reaction channel also the (p,n) reactions can simultaneously be measured. As a highlight, the first (p,g) and (p,n) cross-sections for radioactive 118Te could be investigated in the vicinity of the Gamow window of the g-process.
Several experiments are planned in Spring 2025 at the ESR, CSRe and the dedicated low-energy CRYRING. Dependent on the progress of these experiment, some fresh results might be available to be reported at the conference.

Speaker: Yury Litvinov (GSI Darmstadt)

19:00 Conference Dinner

Friday 20 June

New Facilities and Techniques

70 Measuring decays of excited states in $^{26}$Si to improve reaction rate calculations of $^{22}$Mg$(\alpha, p)^{25}$Al relevant to type I X-ray bursts

The K600 magnetic spectrometer and the CAKE silicon detector array form a powerful tool for coincidence measurements in many nuclear physics experiments including nuclear astrophysics. These instruments have been used, among others, in studies measuring proton decays from $\alpha$-unbound states in $^{22}$Mg through the $^{24}$Mg$(p,t)$$^{22}$Mg reaction to study the $^{18}$Ne$(\alpha,p)$$^{21}$Na cross section relevant in type-I X-ray bursts (XRBs). This talk will examine the $^{28}$Si$(p,t)$$^{26}$Si experiment that is scheduled to be performed at iThemba LABS, Cape Town. This reaction can be used in coincidence measurements to study proton decays from $\alpha$-unbound states in $^{26}$Si to determine the cross section and thermonuclear reaction rate of $^{22}$Mg$(\alpha,p)$$^{25}$Al and its influence on type-I XRBs. This talk will also discuss briefly the H-line for nuclear astrophysics at iThemba LABS. This is a dedicated, low-energy beamline for direct measurements using $(p,\gamma)$ reactions and an array of clover detectors.

Speaker: Dr J.W. Brummer (iThemba LABS, Cape Town, South Africa)

71 The E1 and E2 capture amplitudes in 12C(α, γ)16O around the 2.42 MeV resonance.

In stellar evolution, the carbon-to-oxygen (C/O) ratio at the end of He burning is a crucial parameter, which in turn is strongly influenced by the $^{12}\text{C}(\alpha, \gamma)^{16}\text{O}$ reaction rate. Accurate extrapolation of experimentally measurable cross sections to stellar conditions requires the determination of the E1 and E2 capture amplitudes in the fundamental state of $^{16}\text{O}$. This is particularly difficult in the energy range $2.0 < E_{\text{cm}} < 2.6$ MeV, where the E1 capture through the $E_{\text{cm}} = 2.4$ MeV, $J = 1^-$ resonance dominates the cross section, making it difficult to observe the expected rapid fluctuation of both the E1/E2 amplitude ratio and their mixing phase angle ($\phi_{12}$). Existing measurements of $\gamma$-ray in this energy region weakly constrain these parameters because of a poor signal-to-background ratio and uncertainties in the carbon target stoichiometry. We present a new experiment, in which a NaI detector array with large angular coverage is used in conjunction with the European Recoil mass separator for Nuclear Astrophysics (ERNA). The reaction is initiated by a $^{12}\text{C}$ ion beam impinging onto the ERNA He gas jet target, where $\gamma$-rays are detected. The delayed coincidence condition with $^{16}\text{O}$ recoils provides essentially background-free $\gamma$-ray spectra, opening up the perspective of determining E1 and E2 amplitudes and the associated mixing angle with unprecedented accuracy and precision. The experiment will be presented and the results of the first measurement campaigns will be discussed.

Speaker: K. Chakraborty (Dipartimento di Matematica e Fisica, Università della Campania “L. Vanvitelli”, Caserta, Italy and Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Napoli, Italy)

72 Neutron-Induced Reactions in a High-Density Inertial Confinement Plasma and Their Nuclear Astrophysics Nexus

The thermodynamic conditions of plasma density, temperature, pressure, and the neutron density during the implosion of a deuterium-tritium (DT)-filled capsule by laser-induced inertial confinement at the National Ignition Facility (NIF) constitute a unique stellar-like laboratory environment. In this study, we investigated neutron-induced reactions on Ar seeds added to the DT capsule, specifically the 40Ar(n,2n)39Ar (268 years) and 40Ar(n,γ)41Ar (110 min) reactions; we also searched for the signature of a rapid two neutron capture 40Ar(2n,γ)42Ar (32.9 years) reaction, similar to the r-process occurring in stellar explosive nucleosynthesis. We conducted in parallel direct experiments to measure for the first time the total cross-section of the 40Ar(n,2n)39Ar reaction using a 14-MeV neutron activation. The resulting long-lived argon 39,42Ar isotopic residues were analyzed by Noble Gas Accelerator Mass Spectrometry at the ATLAS accelerator (Argonne National Laboratory) while shorter-lived 41Ar was detected by -spectrometry shortly after implosion at NIF. Preliminary results of 39,41,42Ar yields and comparison with simulations will be presented.

The Authors acknowledge U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02- 06CH11357. This research used resources of ANL’s ATLAS facility, which is a DOE Office of Science User Facility. Pazy Foundation (Israel), USA-Israel Binational Foundation (BSF Grant Nr. 2020136), Israel Science Foundation (ISF Grant Nr 3265/24), Career Research Program (Fusion Energy Sciences) under Grant No. FWP SCW1658, National Science Foundation Grant No. NSF PHY-2011890 and the Nuclear Regulatory Commission, Award No. 31310019M0037 are gratefully acknowledged.

Speaker: Michael Paul (Hebrew University of Jerusalem)

Special Session: Remembering Don Clayton, Roberto Gallino & Karl-Ludwig Kratz

10:15 Coffee Break

Gravitational Waves and Nuclear Astrophysics

73 Exploring dense matter physics with gravitational wave detections of neutron stars

Highly dense and isospin asymmetric matter is partly out of the reach of nuclear laboratories on Earth. Our theoretical understanding of strong and nuclear forces at high density and relatively low temperatures is also limited such that the equation of state and properties of dense matter remains a mystery. However, this particular type of matter comprises the deepest shells of the highly compact astrophysical objects that are neutron stars. An entire field of nuclear astrophysics is devoted to exploring dense matter physics with multi-messenger observations of neutron stars throughout their lifetime. A boost to this field recently occurred with the construction of several gravitational wave detectors that can observe the ripples of space time originating from the coalescence of compact objects.
In this talk, we discuss the advances made on the subject of dense matter physics thanks to the detection of the gravitational waves emitted by neutron star mergers. First, we present our current network of gravitational wave detectors, comprised of LIGO Hanford, LIGO Livingston, Virgo and KAGRA ground based interferometers. We then present the key sources gathered in the recent catalog GWTC-3 of the LIGO-Virgo-KAGRA collaboration and discuss in detail the link between dense matter and the deformation of neutron stars, and its imprint on the gravitational waveform. Particular attention is paid to the most informative source to date, GW170817, and how it has constrained the equation of state of dense matter. We quickly expand on the ability of binary coalescences to help us understand heavy-element nucleosynthesis, using the example of the mass-gap event that occurred during the fourth observing run of the LIGO-Virgo-KAGRA collaboration. Finally, we present what to expect from future observations and the next generation of ground based gravitational wave detectors (Cosmic Explorer and Einstein Telescope) and discuss some of the challenges we shall face in an era of high precision gravitational waves detections.

Speaker: Dr Lami Suleiman (California State University, Fullerton)

74 Quark-Matter Equation of State Effects during Binary Neutrons Star Mergers

In previous work [1] we demonstrated that a crossover transition from hadronic to quark matter during the merger of binary neutron stars can lead to interesting observational consequences in the emergent gravitational waves. In particular, quark matter may cause increased pressure in the crossover density region (2-5 times the nuclear saturation density). This could lead to an extended duration of high frequency (~ 2-3 kHz) gravitational wave emission during the post-merger hyper-neutron-star epoch. However, that study was based upon the QHC19 formulation[2] of the crossover equation of state. The updated QHC21 [3] equation of state has been developed motivated by NICER observations indicating larger radii for neutron stars and even higher pressures in the crossover regime. In this talk we will discuss simulations of neutron-star mergers based upon various equations of state including the QHC21 and QHC19 EoS. In comparison with the previous results we find that the long duration post-merger gravitational-wave emission is even more pronounced when using the QHC21 EoS. Prospects for the detection of the GW emission in the spectral density function via current and future GW observatories will be discussed.
[1] A. Kedia, H. I. Kim, I.-S. Suh, and G J. Mathews, Phys. Rev. D 106, 103027 (2022).
[2] G. Baym, S. Furusawa, T. Hatsuda, T. Kojo, and H. Togashi, Astrophys. J. 885, 42 (2019).
[3] T. Kojo, G. Baym, and T. Hatsuda, Astrophys. J., 934, 46 (2022).

Work at the University of Notre Dame was supported by DOE nuclear theory grant DE-FG02-95-ER40934.

Speaker: Grant Mathews (University of Notre Dame)

75 Inference of multi-channel r-process element enrichment in the Milky Way using neutron star merger observations

Observations of GW170817 strongly suggest that binary neutron star mergers produce rapid neutron-capture nucleosynthesis (r-process) elements. However, it remains an open question whether these mergers can account for al the r-process element enrichment in the Milky Way's history. In particular, the neutron star merger-only enrichment scenario has been shown to be inconsistent with the observed r-process abundance trend of stars in the Galaxy. In this talk, I wil show the constraints on the contributions of the neutron star merger channel using recent astrophysical neutron star observations, including gravitational waves, radio, X-ray, and gamma-ray observations. I will then present a Bayesian framework to consistently combine these lines of observations with r-process abundance data to quantify the contribution and uncertainties of single and multiple astrophysical enrichment sources.

Speaker: Hsin-Yu Chen (The University of Texas at Austin)

76 Gravitational Waves and Nucleosynthesis of Binary Neutron-Star Simulations

Understanding gravitational-wave observations of binary neutron star mergers requires a knowledge of high-density matter. In turn, the electromagnetic signal is by-and-large determined by r-process elements and hence it requires accurate knowledge of the underlying nucleosynthesis processes. In this talk, I will present first nuclear physics results that aim at elucidating the thermal properties of high-density nuclear matter and discuss their potential impact in BNS simulations. I will then discuss the results of numerical-relativity simulations of BNS mergers subject to nonconvex dynamics, allowing for the appearance of expansive shock waves and compressive rarefactions. Finally, I will briefly discuss the r-process nucleosynthesis of ejecta postprocessing in these simulations employing WinNet.

Speaker: Giuseppe Rivieccio (Universitat de Valencia)

NIC XVIII - Giuseppe Rivieccio.pdf

NIC XVIII - Giuseppe Rivieccio.pptx

77 Constraining Skyrme-based neutron star equation of state from multi-messenger observations

Neutron star equations of state based on Skyrme-interaction are one of the most widely used models to describe ultra-dense nuclear matter at the interior of these degenerate stars. In this presentation, I will discuss the effect of various Skyrme parameters on the stellar structural properties of a neutron star and its observables. I will also briefly present the potential source of biases in Bayesian inferences from astrophysical observations of gravitational waves and x-ray emissions, along with some of the possible avenues to mitigate them.

Speaker: Arunava Mukherjee (Saha Institute of Nuclear Physics, Kolkata)

78 3D core-collapse supernova models with phenomenological treatment of neutrino flavor instabilities

We perform three-dimensional supernova simulations with a phenomenological treatment of neutrino flavor conversions. We show that the explosion energy can increase to as high as $\sim10^{51}$ erg depending on the critical density for the onset of flavor conversions, due to a significant enhancement of the mean energy of electron antineutrinos. Our results confirm previous studies showing such energetic explosions, but for the first time in three-dimensional configurations. In addition, we predict neutrino and gravitational wave (GW) signals from a nearby supernova explosion aided by flavor conversions. We find that the neutrino event number decreases because of the reduced flux of heavy-lepton neutrinos. In order to detect GWs, next-generation GW telescopes such as Cosmic Explorer and Einstein Telescope are needed even if the supernova event is located at the Galactic center. These findings show that the neutrino flavor conversions can significantly change supernova dynamics and highlight the importance of further studies on the quantum kinetic equations to determine the conditions of the conversions and their asymptotic states.

Speaker: Kanji Mori (National Astronomical Observatory of Japan)

79 Closing Remarks

Speakers: Gabriel Martinez-Pinedo (GSI), Gabriel Martínez-Pinedo, Gabriel Martínez-Pinedo (GSI Helmholtzzentrum für Schwerionenforschung GmbH, Technische Universität Darmstadt), Gabriel Martínez-Pinedo (GSI Helmholtzzentrum for Heavy Ion Research)

80 Farewell

Speakers: Jordi Jose (UPC), Jordi José (UPC)