Astrophysics with Radioactive Isotopes 2026, Traverse City, MI, USA

26 May 2026, 08:00 → 30 May 2026, 12:00 US/Eastern

The Hagerty Center, Traverse City, Michigan, USA

Scientific Rationale

Radioactive nuclei play a significant role in many current astrophysical pursuits, from the origin of the elements to the driving of emissions from supernovae ($^{56}$Ni) and kilonovae (r-process radioactivity). Radioactive nuclei are crucial for direct studies of galactic enrichment ($^7$Be, $^2$$^6$Al, $^4$$^4$Ti, $^6$$^0$Fe, $^9$$^9$Tc, $^2$$^4$$^4$Pu) and stellar explosions ($^5$$^6$Ni, $^4$$^4$Ti). Stars and their explosions, galaxies and their evolving interstellar medium, and the origin of the solar system are among the targeted astrophysical objects. Stardust, meteorites, ocean floor deposits, cosmic-rays, and gamma-ray spectroscopy provide a rich variety of astronomy to exploit the inherent power of radioactivity. Investigation tools range from numerical models, astronomical instrumentation, and laboratory experiments to derive material compositions and nuclear reaction rates.

The aim of the conference is to bring together researchers interested in the significant role radioactive nuclei play in the cosmos and particularly with respect to questions in astrophysics.  The scientific program will cover topics related to the role of radioactivity within galactic chemical evolution, cosmochemistry, the origin of elements, and multi-messenger astronomy.

This is the latest in a series of conferences organized every couple of years and is open to researchers in the various relevant fields including nuclear physics experiment and theory, astronomy, and astrophysics. The purpose of the conference is to provide all participants and particularly early-career researchers with an opportunity to present their work. The format of the meeting will be designed to foster exchange of ideas, learning, and discussion among participants.

The scientific topics include:

• Nucleosynthetic processes
• Early Solar System record
• Stardust and presolar grains
• AI/ML techniques in data analysis and modeling
• Experiments with, and observations of radioactive isotopes
• Gamma-ray astronomy
• Meteorites and their isotopic signatures
• Metal-poor stars and stellar remnants
• Modeling of supernovae and neutron star mergers
• Cosmology and Big Bang nucleosynthesis
• Radioisotopes in planetary formation, evolution, and heat production.

 

 

---

 

 

Awri26_poster.png

Tuesday 26 May

08:00 Registration

Morning I

1 Radioactive Isotope Production: Understanding the Effects of the Supernova Explosion

A number of supernova engines are thought to contribute to the growing menagerie of transients produced by stellar collapse. Gamma-ray observations of the decay of radioactive isotopes provide one of the most direct probe of these engines with the potential to not only distinguish between different engines but also probe the nature of specific engines. Here I review the differences in the engines as well as the radioactive isotope yield predictions (and their uncertainties) from these different engines.

Speaker: Chris Fryer (Los Alamos National Laboratory)

2 Physical Conditions for Synthesis of Sc, Ti, and V in Neutrino-driven Supernovae

A core-collapse supernova (CCSN) is an explosion of a massive star at the end of their life. The explosion mechanism has not yet been clarified in spite of studies for long time. In this study, we focus on nucleosynthesis as a clue to understand the explosion mechanism. Because CCSNe have driven chemical evolution of the Universe, metal-poor stars born in the early Universe remain the nucleosynthesis results of CCSNe of first stars. Therefore, it is one of the important challenges in nucleosynthesis simulations to reproduce the chemical compositions of metal-poor stars. Recent observation shows correlations among [Sc/Fe], [Ti/Fe], and [V/Fe]. However, the abundance ratios have not been reproduced by numerical simulations.
Then, we perform nucleosynthesis simulations a core-collapse supernova including the neutrino process. Using the Si layer of a $13M_\odot$ zero-metal progenitor as the initial composition, we calculate the nucleosynthesis by adopting the temperature, density, neutrino flux, and duration of nucleosynthesis as arbitrary parameters and compare the results with the observed abundance ratios of Sc, Ti, and V in very-metal-poor (VMP) stars taken from the Stellar Abundances for Galactic Archaeology database.
We find that, to reproduce the abundance ratios in the VMP stars, the explosive nucleosynthesis should take place under the neutrino exposure, which is the time integration of the neutrino flux, of $\sigma_\nu\sim10^{35}\,\mathrm{erg\,cm^{−2}}$ and temperature of $2.0\,\mathrm{GK} \leq T \leq 3.2\,\mathrm{GK}$.
We also discuss whether the quantitative requirements are realized during the explosion. Although the requirements are difficult to realize in the one-dimensional simulations, the nonmonotonic thermal evolution shown in recent three-dimensional simulations may satisfy them. Because the evolution is likely caused by turbulent motion stemming from the initial asphericity of the progenitor, it is important to calculate the long-term three-dimensional supernova explosion of multidimensional metal-free progenitor models and follow the nucleosynthesis self-consistently in the future.

Speaker: Ryota Hatami (SOKENDAI/NAOJ)

3 Gamma rays as a signature of r-process producing supernovae: remnants and future Galactic explosions

We consider the question of whether core-collapse supernovae (CCSNe) can produce rapid neutron
capture process (r-process) elements and how future MeV gamma-ray observations could address this.
Rare types of CCSNe characterized by substantial magnetic fields and rotation, known as magnetorotational supernovae (MR-SNe), are theoretically predicted to produce these elements, although direct
observational evidence is lacking. We suggest that this critical question be addressed through the
study of some of the eleven CCSN remnants located within 10 kpc, as well as through the detection
of gamma-ray emission from a future Galactic supernova. We use a two-dimensional MR-SN model
to estimate the expected gamma flux stemming from nuclear decays in the range of a few tens of keV
to a few MeV. Our results indicate that an observation of 126Sn (126Sb) in a remnant stands out as
a signature of an r-process-producing supernova. Since the neutron-rich conditions that lead to the
production of the r-process could also enhance the production of 60Fe, the detection of substantial 60Fe
(
60Co) would be indicative of favorable conditions for the r-process. In the case of a future supernova
explosion, when the evolution of the spectrum is studied over ten days to a few years, a rich picture
emerges. At various epochs, second peak r-process isotopes such as 125Sn, 131I, 131Te, 132I and 140La
produce gamma-ray signals that emerge above the background from explosive burning products and
electron–positron annihilation. The weak r-process isotopes 95Nb, 103Ru, 106Rh also have periods of
prominence. While MR-SNe are predicted to have a relatively small main r-process contribution, third
peak isotopes like 194Ir could still be above next generation MeV gamma instrument sensitivities.

Speaker: Zhenghai Liu (North Carolina State University)

10:20 Coffee Break

Morning II

4 Radioactive Isotopes in Presolar Supernova Grains

Presolar grains are microscopic meteoritic dust particles that condensed in the outflows of ancient stars and supernova ejecta before the formation of the Solar System, preserving a direct isotopic record of stellar nucleosynthesis and astrophysical processes. Most presolar grains originate from asymptotic giant branch (AGB) stars and core-collapse supernovae (CCSNe) [1]. Due to the long evolutionary timescales of AGB stars, only relatively long-lived radionuclides such as 26Al (t1/2 = 0.72 Ma) and 41Ca (t1/2 = 0.1 Ma) have been detected in AGB-derived grains, e.g., [2]. In contrast, the rapid explosive nucleosynthesis in CCSNe produces a wide range of short-lived radioactive isotopes, which could be incorporated into dust condensing shortly after the explosion. Previous studies have identified 26Al, 41Ca, 32Si (t1/2 = 172 a), 44Ti (t1/2 = 60 a), and 49V (t1/2 = 330 d) in presolar supernova grains [3–7].

In this study, we systematically investigated isotopes from C to Cu in presolar supernova SiC grains isolated from the Murchison meteorite. High-resolution NanoSIMS ion imaging was employed to minimize contamination, ensuring accurate determination of intrinsic stellar signatures. We report the first detection of 63Ni (t1/2 = 100 a) in presolar supernova grains, along with spatial correlations of 26Mg with 27Al and 44Ca with 48Ti, confirming the initial presence of 26Al and 44Ti – the parent isotopes of 26Mg and 44Ca, respectively. Our new inferred initial abundances of 32Si, 41Ca, and 63Ni – produced by neutron-burst nucleosynthesis in He-rich layers during the explosion [8] – allow us to assess uncertainties in (n,γ) cross sections and to constrain neutron exposure conditions, providing insights into the explosion energies of their parent CCSNe.

Furthermore, our new Ti isotope data support an earlier finding that supernova SiC grains condensed after the decay of 49V (t1/2 = 330 d) [7]. This aligns with the incorporation of a substantial amount of 137Ba, the decay product of 137Cs (t1/2 = 30 a) [9], indicating late-stage SiC grain formation following the explosions of their supernovae.

Radioactive isotopes in presolar supernova grains serve as powerful tracers of explosion dynamics, nucleosynthesis pathways, and grain formation timing, offering unique insights into the physical conditions and processes governing CCSNe.

References: [1] Liu N. (2025) Treatise on Geochemistry (Third Edition) 7: 113–145. [2] Nittler L. R. et al. (2008) The Astrophysical Journal 682: 1450–1478. [3] Amari S. et al. (1996) The Astrophysical Journal 470: L101–L104. [4] Nittler L. R. et al. (1996) The Astrophysical Journal 462: L31–L34. [5] Hoppe P. et al. (2002) The Astrophysical Journal 576: L69–L72. [6] Pignatari M. et al. (2013) The Astrophysical Journal Letters 767: L22. [7] Liu N. et al. (2018) Science Advances 4: eaao1054. [8] Meyer B. S. et al. (2000) The Astrophysical Journal 540: L49–L52. [9] Ott U. et al. (2019) The Astrophysical Journal 885: 128.

Speaker: Nan Liu (Boston University)

5 Short-lived nuclides in the early Solar System: an update

A 2022 review of the abundances of radioactive isotopes at the time of Solar System formation [1] is updated, based on new observations and inferences over the past five years. The key isotopes for early Solar System chronology are $^{26}$Al , $^{53}$Mn, and $^{182}$Hf.
$^{26}$Al is very useful as a relative chronometer and is present in high enough abundance in the early Solar System to be a potent heat source for melting asteroids. A database of $^{26}$Al-$^{26}$Mg internal isochrons from calcium-, aluminum-rich inclusions (CAIs), the first objects to form in the Solar System, has recently become available [2]. It reinforces the early Solar System $^{26}$Al/$^{27}$Al value of 5.2×10$^{-5}$ and shows that most CAIs formed with $^{26}$Al/$^{27}$Al > 4.0×10$^{-5}$, or within the first 300,000 a of Solar System formation. The $^{26}$Al-$^{26}$Mg system seems to be robust as a relative chronometer for CAIs, chondrules, and early-formed differentiated meteorites. There remains a puzzle of why some hibonite-rich CAIs with large nucleosynthetic anomalies in $^{48}$Ca and $^{50}$Ti contained little $^{26}$Al when they formed, but these objects appear to have formed early and were exposed to a greatly enhanced solar cosmic ray flux [3].
$^{53}$Mn is a useful chronometer for chondrules and differentiated meteorites. The early Solar System $^{53}$Mn/$^{55}$Mn ratio must be established indirectly, as manganese is not a refractory element and CAIs have low Mn/Cr ratios; the measured half-life is also rather uncertain, 3.7±0.4 Ma. A statistical treatment of the $^{26}$Al-$^{26}$Mg, $^{53}$Mn-$^{53}$Cr, $^{182}$Hf-$^{182}$W, and Pb-Pb systems in achondritic meteorites of volcanic origin inferred that the most probable early Solar System $^{53}$Mn/$^{55}$Mn ratio is (8.09±0.65)×10$^{-6}$ and the $^{53}$Mn half-life is 3.80±0.23 Ma [4].
$^{60}$Fe was once thought to have been abundant enough to serve as a heat source for asteroidal melting, with $^{60}$Fe/$^{56}$Fe ratio as high as 1.5×10$^{-6}$ [5], but this was based on a measured half-life shorter by nearly a factor of 2 than the currently accepted value and on a large decay correction. A decade ago, the $^{60}$Fe/$^{56}$Fe ratio was inferred to be as high as 7×10$^{-7}$, based on secondary ion mass spectrometry of chondrule silicates [6]. Resonance ionization mass spectrometry of these silicates showed that the high $^{60}$Fe/$^{56}$Fe ratio was likely an artifact of mass fractionation corrections during data reduction [7]. High precision nickel isotopic measurements of meteorites showed that the early Solar System ratio was ~1×10$^{-8}$ [8]. Recent measurement of the unique achondrite Erg Chech 002, which crystallized <2 Ma after CAI formation, show that the early Solar System $^{60}$Fe/$^{56}$Fe ratio was (7.71±0.47)×10$^{-9}$ [9]. The low $^{60}$Fe/$^{56}$Fe and high $^{26}$Al/$^{27}$Al in the early Solar System remain a challenge, as both $^{60}$Fe and $^{26}$Al are made in core-collapse supernova. Decoupling them by carrying $^{26}$Al in winds of Wolf-Rayet stars may be a way out of this conundrum [10].

[1] Davis A. M. (2022) ARNPS 72, 339–363. [2] Dunham E. T. et al. (2026) ApJS 282, 11. [3] Kööp L. et al. (2018) Nature Astron. 2, 709–713. [4] Desch S. J. et al. (2023) Icarus 402, 115611. [5] Shukolyukov A. & Lugmair G. W. (1993) Science 259, 1138–1142. [6] Telus M. et al. (2018) Geochim. Cosmochim. Acta 221, 342–357. [7] Trappitsch et al. (2018) ApJL 857, L15. [8] Tang H. & Dauphas N. (2015) ApJ 802, 22. [9] Fang L. et al. (2025) Science Adv. 11, eadp9381. [10] Dwarkadas V. V. et al. (2017) ApJ 851, 147.

Speaker: Andrew M. Davis (University of Chicago)

11:50 Lunch Break

Afternoon I

6 The Future of Gamma-ray Instruments: COSI and the Remaining MeV Gap

The future of gamma-ray missions is currently under discussion. The FIGSAG Report highlights science cases that can only be addressed with future gamma-ray missions and primarily points toward the need for large payloads to achieve sensitivities exceeding Fermi by over an order of magnitude in both the MeV and GeV regimes in order to answer key questions about blazar jets and build a pulsar timing array to capture supermassive black hole mergers. However, in writing the report, it also became clear that a single technology will not be well suited to answer all of the profound questions posed in the gamma rays. While a high-effective area and a large field of view is needed for some questions, high angular resolution is needed to answer others.

COSI is a Small Explorer class mission expected to launch in 2027. It will survey the soft gamma-ray sky in 0.2-5 MeV, with a primary field of view of >25% of the sky instantaneously. Its germanium detectors were specifically designed for high energy resolution to focus on the study of annihilation and nuclear lines. COSI will image the Galaxy in 511 keV and several nuclear lines to determine substructure, especially in the Galactic Bulge. Looking into the future, COSI will be a pathfinder for both, future missions with focussing optics optimized for deep, narrow-field observations, and missions with large effective area to observe the whole gamma-ray sky.

Speaker: Tiffany Lewis

7 Toward all-sky gamma-ray line surveys with COSI

Precise measurements of nuclear line emissions have revealed the nature of ongoing chemical enrichment in the Milky Way. Observations of $^{56}$Ni, $^{44}$Ti, and $^{26}$Al have provided unique insights into the dynamics of supernova explosions and the flow of material in the interstellar medium. With a scheduled launch in 2027, the Compton Spectrometer and Imager (COSI) will offer new potential to push these frontiers. COSI will create all-sky maps in the 0.2–5 MeV bandpass with unprecedented flux sensitivity and high spectral resolution. It will provide the first galactic map of $^{60}$Fe, resolve finer structures of $^{26}$Al, and continue the quest to uncover hidden supernova remnants. To maximize COSI’s spectral and imaging returns, increasingly realistic simulations and pipeline development efforts are underway. Characterizing and mitigating the impact of a harsh space radiation environment is especially crucial to maximize COSI’s inflight performance. In this talk, I will present an overview of the nucleosynthesis science enabled by COSI, the advances we can expect, the status of our data simulations and analysis pipeline, and the big challenges on our way toward deeper, all-sky surveys with COSI.

Speaker: Aravind Valluvan (UC San Diego)

15:30 Coffee Break

Afternoon II

8 When Stars Attack! Astrophysical Implications of Live 60Fe and 244Pu in Terrestrial and Lunar Archives

Recent nearby stellar explosions can deliver their ejecta to the Earth and Moon, leaving a telltale signature in the form of live (not decayed) radioisotopes in the geological record. Remarkably, there is now a wealth of evidence that this has occurred: live ${}^{60}{\rm Fe}$ is found globally and in lunar regolith samples, and recently ${}^{244}{\rm Pu}$ is also detected. These point to recent supernova activity but also to r-process activity. We will discuss the astrophysical implications of these detections, including (a) the mechanisms needed to deliver explosion debris to the Earth, (b) the progenitor scenarios that can account for the data, and (c) the tests that could distinguish among the possibilities while offering a new probe of the r-process. The larger lesson is that these recently-arrived radioisotopes represent a new kind of cosmic messenger, and that fully understanding their story requires that we weave together not only a wealth of astrophysics, but also nuclear physics, geology, and astrobiology.

Speaker: Brian Fields (University of Illinois)

16:20 Discussion

17:00 Welcome Reception

Wednesday 27 May

Morning I

9 Galactic radioactive links to rocky worlds

The thermal evolution of rocky exoplanets is modulated by (i) left-over (gravitational) heat of accretion, and (ii) radiogenic heating from the decay of long-lived radioactive isotopes, particularly 40^K, 232^Th, 235^U, and 238^U. These heat-producing elements (HPEs) are synthesized through distinct nucleosynthetic pathways and evolved in both relative and absolute abundance over time as traced via galactic chemical evolution (GCE) – and where possible – direct or proxy spectroscopic observations. We synthesize current understanding of how GCE processes control the radiogenic heat budgets of rocky exoplanets by mapping HPEs across different stellar populations in the Milky Way. Combining GCE models with thermal evolution simulations reveals that planets forming around older, metal-poor stars possess significantly lower initial radiogenic heat inventories compared to younger, metal-rich systems. Depending on the HPE, initial radiogenic heat production in Earth-mass planets can vary by a factor of 2–10 between different stellar environments. We explore how this variation impacts planetary geodynamics, magnetic dynamo generation, volcanic activity and secondary atmosphere outgassing, as well as biocompatibility. We present theoretical models showing that stagnant-lid rocky exoplanets around old stars may exhaust their radiogenic heat budgets within 2–4 Gyr, potentially entering Venus-like states and losing their capacity to maintain temperate climates through carbon cycling. Conversely, planets with enhanced HPE abundances may experience excessive radiogenic heating, leading to prolonged magma ocean phases, hyper-volcanism or dynamo failure. We identify a "metallicity Goldilocks zone" near solar values where persistent magnetic dynamos can be sustained. Our analysis demonstrates that the galactic context of planetary formation - encoded in stellar metallicity, age, and nucleosynthetic history of the HPEs - governs both long-term thermal evolution and an exoplanet’s biocompatibility.

Speaker: Stephen J. Mojzsis (University of Bayreuth, Bavarian Geoinstitute (BGI))

10 An alternative source of $^{44}$Ti in Supernova Remnants

Core-collapse supernovae can synthesize $^{44}\rm Ti$ during the explosion via explosive Si-burning and $\alpha$-rich freeze-out. This radioactive isotope with a half-life of $\sim 60$ years is then observed in supernova remnants, particularly Cassiopeia A, by gamma-ray telescopes, such as the upcoming COSI mission. In this talk, I will discuss an alternative production site of $^{44}\rm Ti$ in core-collapse supernovae, i.e. Carbon-Oxygen shell mergers. These are mergers of the C-shell and O-shell that occur a few hours before collapse. They have very peculiar nucleosynthetic signatures, producing heavier $\alpha$-elements and destroying lighter ones, resulting in higher ratios of Ar/Ne, Si/Ne, S/Ne compared to progenitors that did not experience such mergers. I will show that these elemental ratios predicted by neutrino-driven explosion models of progenitors undergoing C-O shell mergers agree with observations of Cas-A. Then, I will discuss the production of titanium, and compare our predictions to the sensitivity of existing (NuSTAR) and future (COSI) gamma-ray telescopes.

Speaker: Luca Boccioli (UC Berkeley)

11 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 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: Dr Benjamin Wehmeyer (University of Wroclaw)

10:20 Coffee Break

Morning II

12 Nucleosynthesis in C-O shell mergers in massive stars

Carbon-oxygen (C-O) shell mergers 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 some of their (short-lived) radioactive isotopes as $^{36}$Cl and $^{40}$K. 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 a very peculiar nucleosynthetic signature.

Speaker: Lorenzo Roberti (INFN)

13 Radioactive isotope formation in 3D-informed O-C shell mergers

O-C shell mergers in massive stars are astrophysical sites for the production of many radioactive isotopes such as $^{40}\mathrm{K}$, which heats rocky exoplanets, and $^{44}\mathrm{Ti}$ and $^{60}\mathrm{Fe}$, which are observed in supernova remnants. Mixing prescriptions used in 1D stellar evolution models of stars with O-C shell mergers do not capture features seen in 3D hydrodynamic simulations, such as more efficient mixing that decreases near the boundaries.

In this talk I will present the results of modifying the mixing profile of an O shell during a merger of a $15~\mathrm{M_\odot}$ $Z=0.02$ star informed by 3D macrophysics. Across different mixing scenarios, the predicted pre-explosive yields of radioactive isotopes can vary by multiple orders of magnitude, and yields of $^{40}\mathrm{K}$, $^{44}\mathrm{Ti}$, and $^{60}\mathrm{Fe}$ in particular by factors of $788$, $60847$, and $46$ respectively. Further, depending on the mixing, the pre-explosive yields of $^{40}\mathrm{K}$ and $^{44}\mathrm{Ti}$ can be larger than the explosive contributions. I will discuss the implications of this work for understanding rocky planet heating and interpreting the signals from supernova remnants like Cassiopeia A.

Speaker: Mr Joshua Issa (University of Victoria)

11:50 Lunch Break

Afternoon I

14 Chemical evolution of Milky Way-like galaxies with zoomed-in cosmological simulations including long-term radioactive elements

In this talk, I will discuss the chemical evolution of Milky Way-like galaxies with zoomed-in cosmological simulations including long-term radioactive elements. The simulated galaxies considered here are representative of MW-like galaxies according to a range of properties, that include morphology, masses, star formation rate, distribution of chemical abundances. Our simulations have already been tested to reproduce the chemical evolution of α-elements and dust evolution in MW-like galaxies. In this work, we have extended the chemical evolution network of our simulations in order to account also for 40K, and Eu, Th and U. We will then show the predicted abundance patterns for various chemical elements, including long-term radioactive elements. We will also show the distribution maps of radioactive elements across the simulated MW-like galaxies. Finally, we will couple the outputs of our simulations with a mineralogy code to study the potential statistics of Earth-like habitable planets in the Milky Way, thus putting constraints on the Galactic habitable zone.

Speaker: Valeria Grisoni (INAF Trieste)

15 Chemical Separation of Presolar Grains from Meteorites

Presolar grains are solid stardust particles with very little physical, chemical, or aqueous alteration, making them perfect for direct analysis of stellar processes in the stars that created the material for our solar system. Trace isotopes in presolar grains can tell us about the nucleosynthetic processes occurring in the stars that formed them. Searching for grains in situ can take extensive time, instrumentation use, and requires additional steps to isolate the grain from the meteorite matrix to observe grain morphology. We are using a modified Chicago method [1,2] to chemically separate presolar grains from two meteorites, Murchison and Oued Chebeika 002 (OC 002). Murchison is a well-studied CM chondrite and the source of the majority of published presolar grain data, but OC 002 is a new (2024) find and is the most pristine CI meteorite available [3].
Most meteorites and planets belong to either the carbonaceous (CC) or noncarbonaceous (NC) groups, based on nucleosynthetic isotopic anomalies in many elements. There is growing evidence that the CI meteorites, along with asteroids Ryugu and Bennu (from which samples have been returned to Earth by spacecraft) comprise a third isotopic group; the question arises of whether the CIs have the same population of presolar grains as CCs. Presolar grain separations of CIs have only been completed on Orgueil [4,5]. Through acid treatments, and density and/or size separations, we aim to extract presolar nanodiamonds, refractory minerals, graphite, and silicon carbide. We plan to use nanoscale secondary ion mass spectrometry to quantify isotopic ratios of C, N, and Si on presolar SiC and C and N on graphite grains, which will determine the grain classification [6,7]. Using the CHicago Instrument for Laser Ionization (CHILI) [8], a resonance ionization mass spectrometer, we aim to quantify the isotopic ratios of trace elements affected by branch points in the s-process such as Ba, Mo, Zr, and Sr from the presolar grains extracted in this separation. This will reveal the conditions such as the neutron density or metallicity in neutron capture nucleosynthesis that occurred in the parent stars.

[1] Amari S et al. (1994) Geochim. Cosmochim. Acta 58:459–470. [2] Korsmeyer JM (2025) PhD dissertation, The University of Chicago. [3] Gattacceca J et al. (2025) Meteoritics Planet. Sci. 60:1441–1479. [4] Jadhav M et al. (2013) Geochim. Cosmochim. Acta 113:193–224. [5] Huss and Lewis (1995) Geochim. Cosmochim. Acta 59, 115-160. [6] Amari S et al. (2014) Geochim. Cosmochim. Acta 133:479–522. [7] Stephan T et al. (2024) Astrophys. J. Suppl. Ser. 270:27. [8] Stephan T et al. (2016) Int. J. Mass Spectrom. 407:1–15.

Speaker: Liv Mumma (University of Chicago)

15:30 Coffee Break

Afternoon II

16 Single Degenerate Double Detonation Type Ia Supernova from Quiescent Helium Accretion

We investigate a sub-Chandrasekhar mass double detonation pathway for Type Ia supernovae arising from single degenerate helium accreting carbon-oxygen white dwarfs. Using one-dimension recurrent nova evolution code we evolve a 0.7 solar mass white dwarf through steady accretion at 10^-8 solar mass per year until it reaches 1.1 solar mass, yielding realistic, time evolved helium rich profiles. These profiles are mapped into FLASH simulations, incorporating nuclear burning for helium and carbon-oxygen detonation, in multi-dimensional hydrodynamic runs. A localized, modest temperature perturbation near the base of the helium shell robustly triggers an outward helium-shell detonation. The ensuing inward propagating shock converges in the carbon-oxygen core, igniting a secondary detonation that unbinds the star. We obtain a Ni56 yield of ~0.64 solar mass, an intermediate-mass element (Si-Ca) mass of ~0.41 solar mass, and maximum ejecta velocities approaching 22,000 km/s, values consistent with normal Type Ia supernovae. Our results demonstrate that recurrent helium accretors, typically quiescent over long timescales, can evolve under subtle, "quiet" conditions to trigger robust double detonations, supporting their role as viable progenitors of sub-Chandrasekhar mass Type Ia supernovae.

Speaker: Dr Amir Michaelis (Technion – Israel Institute of Technology)

17 Lifetime Measurements of 23Mg Excited State Significant in Nova Nucleosynthesis of 22Na

The 1275-keV gamma-ray line from decay of the radionuclide $^{22}$Na (${t _ {1/2}}$ = 2.6 y) is a prominent candidate for detection by space-based gamma ray telescopes, including the COSI mission scheduled to launch in 2027. Accurate models of the production and destruction of $^{22}$Na during novae are sought in order to determine the sensitivity required by observational missions as well as to compare to observational results in the future. During the thermonuclear runaway, the main channel through which $^{22}$Na is consumed is proton capture to $^{23}$Mg, and the thermonuclear rate of this reaction is dominated by a single narrow resonance corresponding to a proton energy of 213 keV. Direct measurements of the strength of this resonance are discrepant, and resonance strengths determined indirectly using the proton branching ratio and the lifetime of the associated 7787 keV state in $^{23}$Mg are in further disagreement with both direct measurements. The Doppler Shift Lifetimes 2 (DSL2) setup at the TRIUMF-ISAC II user facility was used to constrain the lifetime of this key state in $^{23}$Mg. Preliminary results for this lifetime will be presented and interpreted in the context of prior nuclear data discrepancies and impact on the nucleosynthesis of $^{22}$Na in nova models.

This material is based upon work supported by the U.S. National Science Foundation under Grant Nos. PHY-1913554, PHY-2209429, and PHY-2514797. We acknowledge the Natural Sciences and Engineering Research Council of Canada. TRIUMF receives federal funding via a contribution agreement through the National Research Council of Canada. The GRIFFIN infrastructure has been funded jointly by the Canada Foundation for Innovation, the British Columbia Knowledge Development Fund (BCKDF), the Ontario Ministry of Research and Innovation (ON-MRI), TRIUMF and the University of Guelph.

Speaker: Lexanne Weghorn

16:40 Discussion

Thursday 28 May

Morning I

18 Primordial Nucleosynthesis: New Progress on Radioactive and Stable Isotopes

Big-bang nucleosynthesis (BBN) describes the formation of the lightest nuclides in the first minutes of cosmic time, and is a central pillar of the hot big-bang cosmology. Standard BBN combines this with the Standard Model of particle physics and nuclear cross section measurements. These allow us to make tight predictions for the primordial light element abundances, some of which are stable, but mass-7 is mostly produced as the radioisotope ⁷Be that later decays to ⁷Li. We will discuss recent observational and theoretical activity concerning ⁷Li and ⁴He. Lithium observations (in metal-poor halo stars) have long disagreed with BBN predictions, leading to the cosmic "lithium problem." But recent work strengthens the case for a solution to this problem involving stellar destruction of lithium. Turning to ⁴He, we will present new observations that achieved a leap in precision. We will discuss the implications of these observations for cosmology and physics beyond the Standard Model. And we will conclude with recommendations for new astrophysical observations and nuclear physics measurements that can make BBN an even more powerful probe of the early Universe and new physics.

Speaker: Brian Fields (University of Illinois)

19 Studying the NiCu Cycle with the GADGET 2 System

Sensitivity studies have identified the $^{59}$Cu(p, $\gamma$)$^{60}$Zn and $^{59}$Cu(p, $\alpha$)$^{56}$Ni reaction rates as quantities which strongly affect the light curve and ash composition of type I X-ray bursts, and the production of $^{59}$Ni by the $\nu p$ process in supernovae. The relative rates of these reactions will determine the strength of the NiCu cycle: $^{59}$Cu(p, $\alpha$) inhibits production of heavier elements while $^{59}$Cu(p, $\gamma$) allows nucleosynthesis to continue onto heavier elements. Prior experiments have directly measured the $^{59}$Cu(p,$\alpha$) reaction rate above the Gamow window for X-ray bursts, and single nucleon transfer reactions were used to discover resonances and obtain proton spectroscopic factors for resonances within the Gamow window for X-ray bursts.

In November of 2025, FRIB Experiment E23035 used the GADGET II system, which consists of a time projection chamber surrounded by the DEGAi germanium array, to discover resonances in $^{60}$Zn, and measure the associated proton, $\alpha$-particle, and $\gamma$-ray branching ratios. A $^{60}$Ga beam was implanted in the time projection chamber and the $\beta$ decay of $^{60}$Ga populated excited states in $^{60}$Zn, including states within the Gamow windows for both X-ray bursts and the $\nu$p process. The time projection chamber was used to identify and measure the energy of $\beta$-delayed protons and $\alpha$-particles, and the germanium array detected gamma rays. These measurements provide information about the relative rates of $^{59}$Cu(p, $\gamma$) and $^{59}$Cu(p, $\alpha$) reactions, for the first time providing experimental information about competition between the (p,$\alpha$) and (p, $\gamma$) reactions at the energies relevant to the rp and $\nu$p processes. Absolute reaction rates will be calculated by identifying measured resonances with shell model states and using the shell model lifetimes of those states to calculate resonance strengths. Preliminary results including newly discovered resonances and corresponding branching ratios will be presented.

This work has been supported by the U. S. Department of Energy under award no: DE-SC0016052 and DE-SC0024587, and the U. S. National Science Foundation under award no: 1565546, 1913554, 2209429, and 2514797.

Speaker: Alexander Adams (Michigan State University / Facility for Rare Isotope Beams)

20 The Actinide-Boost Star LAMOST J122216.85-063345: A Detailed R-process Abundance Study with Gemini-S/GHOST

We present a detailed chemical-abundance analysis of an actinide-boost (log ϵ (Th/Dy) = –0.74) star, LAMOST J122216.85-063345.2 (J1222), a very metal-poor ([Fe/H] = –2.45) halo star with moderate enhancement in rapid neutron-capture (r-)process elements ([Eu/Fe] = +0.61). From high-resolution spectra (R ∼ 55,000) taken with Gemini-S/GHOST, we determine abundances for 43 elements, including thorium. The abundance pattern of J1222 is consistent with predicted nucleosynthetic yields from neutron star mergers (NSMs) or black hole-neutron star mergers (BH-NSMs), under specific ejecta conditions. Our kinematic analysis of J1222 indicates that it belongs to the I’itoi substructure. A comparative analysis of J1222 and seven other stars from the literature with similar dynamics to the I’itoi substructure exhibits a broad dispersion in r-process enrichment –- spanning non-enhancement ([Eu/Fe] ≤ +0.3), moderate enhancement (+0.3 < [Eu/Fe] ≤ +0.7), strong enhancement ([Eu/Fe] > +0.7), and actinide-boost stars (including an additional candidate actinide-boost star with a high upper limit on thorium newly recognized to be associated with I’itoi), suggesting a complex enrichment history shaped by multiple r-process events and inhomogeneous mixing. After exploring several astrophysical scenarios to explain the observed r-process abundances, we find that NSMs and BH-NSMs were likely the main contributors to the enrichment, while magneto-rotational supernovae (MR-SNe) may have played a secondary role in enriching some light r-process element-rich stars in the I’itoi substructure. We also report on an ongoing analysis of the uranium abundance in this star.

Speaker: Timothy C. Beers (University of Notre Dame)

10:20 Coffee Break

Morning II

21 Radioactivity in supernovae and kilonovae

Supernovae and kilonovae are explosive transients representing the deaths of massive stars and mergers of compact objects. In these explosions many radioactive elements are produced, the decay of which powers much of the electromagnetic display. I review the role of radioactivity in determining the observed supernova and kilonova properties, including the deposition physics and thermalization of gamma rays, leptons, alpha particles, and fission fragments. I then summarize what we have learned about the production of 56Ni, 57Ni, 44Ti, and other isotopes, by observing and modelling supernovae and kilonovae, and discuss what the implications are for progenitor properties and explosion physics. Finally, I outline the links between radioactivity in explosive transients and pre-solar grain compositions and earth deposits.

Speaker: Anders Jerkstrand (Stockholm University)

22 Preparing SECAR for Astrophysically Relevant Radiative Proton Capture Reactions

The Separator for Capture Reactions (SECAR) located in ReAccelerator Hall 3 (ReA3) at the Facility for Rare Isotope Beams (FRIB) is a next-generation recoil separator designed to directly measure radiative capture reaction rates in inverse kinematics. These reactions are critical to understanding phenomena such as X-ray bursts, novae, and supernovae, which play a key role in the nucleosynthesis of elements. As part of its commissioning, efforts are underway to characterize SECAR’s acceptance and beam rejection capabilities, as well as to commission the windowless extended gas target for hydrogen operation. The Bismuth Germanate (BGO) gamma ray detector array surrounding the target has been studied in GEANT4, and an algorithm is being developed to constrain the reaction location within the target. With radioactive beams from FRIB, SECAR will soon be poised to measure previously inaccessible reaction rates, addressing open questions in nuclear astrophysics such as element formation and neutron star crust physics. This presentation will provide an update on SECAR’s commissioning and future scientific prospects.

Speaker: Kenzie Smith (Michigan State University/FRIB)

11:50 Lunch Break

Afternoon I

23 Constraining 44Ti and 56Ni yields via a direct 13N(α,p)16O measurement

The long-lived γ-ray isotopes observed in supernova remnants serve as direct signatures of the nucleosynthesis processes occurring deep within core-collapse supernovae. However, transforming these observations into a clear understanding of explosion dynamics requires precise nuclear physics input. A prime example is the 13-N(α,p)16-O reaction, which has been identified as a major nuclear uncertainty affecting the production of observable isotopes such as 44-Ti, 56-Ni, and various neutron-rich iron-group elements.
In this talk, I will present a new measurement of the 13-N(α,p)16-O reaction cross section performed at the CRIB facility (RIKEN). By employing the thick-target inverse kinematics technique with a high-intensity radioactive 13N beam, we probed the astrophysically relevant energy range of Ec.m.​≈1.2–5.0 MeV. I will discuss our experimental approach and share preliminary results from this experiment, illustrating how targeted nuclear physics measurements provide the critical data needed to refine nucleosynthesis models. These results are essential for improving the interpretation of current γ-ray data and enabling more accurate predictions for next-generation observatories, ultimately allowing us to use γ-ray signatures as detailed probes of stellar explosion physics.

References
[1] K. Hermansen et al., Astrophys. J 901, 77 (2020).
[2] S. Subedi et al., Astrophys. J 898, 5 (2020).
[3] C.L. Fryer et al., arXiv:2601.04464 [astro-ph] (2026).
[4] A. Meyer et al., Phys. Rev. C 102, 035803 (2020).
[5] H. Jayatissa et al., Phys. Rev. C 105, L042802 (2022).

Speaker: Thanassis Psaltis (Saint Mary's University)

15:10 Coffee Break

Afternoon II

24 Implications of a weakening N = 126 shell closure away from stability for r-process astrophysical conditions

The formation of the third 𝑟-process abundance peak near 𝐴 ∼ 195 is highly sensitive to both nuclear structure far from stability and the astrophysical conditions that produce the heaviest elements. In particular, the 𝑁 = 126 shell closure plays a crucial role in shaping this peak. Experimental data hints that the shell weakens as proton number departs from 𝑍 = 82, a trend largely missed by global mass models. To investigate its impact on 𝑟-process nucleosynthesis, we employ both standard global models with strong closures and modified Duflo-Zuker (DZ) models that reproduce the weakening, combined with three sets of 𝛽-decay rates. Strong shell closures generate sharply peaked abundances, whereas weakened closures consistent with the experimental trend produce broader, flatter patterns. Accurately reproducing the solar third peak under weakened shell strength requires sufficiently neutron-rich conditions that significant fission occurs, and slower decay rates. These results demonstrate that a weakening 𝑁 = 126 shell closure away from stability imposes significant constraints on the astrophysical environments of the 𝑟-process and underscores the need for precise mass measurements and improved characterization of 𝛽-decay properties in this region.

Speaker: Mengke Li (UC Berkeley)

16:20 Discussion

18:30 Dinner

Friday 29 May

Morning I

25 Gamma-ray line signatures of i-process nucleosynthesis: detection prospects with COSI

The intermediate neutron-capture process (i process) produces a distinct pattern of rare isotopes at neutron densities between the s and r process. Two candidate sites with predicted rapid mass ejections in the solar neighborhood are post-AGB stars undergoing very-late thermal pulses (e.g. Sakurai's object) and rapidly-accreting white dwarfs (RAWDs). Our 1D and 3D simulations show that the convective-reactive fluid dynamics driving i-process nucleosynthesis leads to violent, non-radial outbursts that eject radioactive material. We calculate ejected yields for isotopes with gamma-ray lines in the 0.5–2 MeV range, including $^{22}$Na, $^{89}$Sr, $^{95}$Zr, and $^{137}$Cs. We estimate that the probability of detecting i-process gamma-ray emission during COSI's prime mission is up to ~1%, rising to ~11% for $^{89}$Sr if the event is caught within days, and ~5% for long-lived $^{22}$Na. Detection of neutron-rich $^{137}$Cs would provide the first direct gamma-ray signature distinguishing intermediate neutron-density nucleosynthesis from s- and r-process pathways, opening a new multi-messenger window on dynamic stellar nucleosynthesis. Future $\gamma$-ray telescopes employing focusing Laue or Fresnel lenses, or liquid-Ar all-sky detectors, could achieve a fiftyfold sensitivity improvement and raise detection probabilities to several tens of percent.

Speaker: Falk Herwig (University of Victoria)

26 Identification of s-wave States in 19Ne and their Effects on the 18F(p,alpha)15O Reaction in Classical Novae

One aim of the upcoming Compton Spectrometer and Imager (COSI), to launch in 2027, is to measure the luminosity of gamma-rays from classical novae, presenting an exciting opportunity to constrain 18F abundance in these astrophysical phenomena. Models of classical novae have determined that nucleosynthesis and detectability of the explosion depend heavily upon the abundance of this isotope; however, precise abundance calculations remain hindered largely due to uncertainties in the rate of its main destruction pathway: the 18F(p,alpha)15O reaction. The largest uncertainties in this reaction rate are the unclear identities and properties of sub- and near-proton-threshold s-wave states in the compound nucleus, 19Ne. In order to more precisely determine the properties of 19Ne excited states, we conducted a 19F(3He,t)19Ne transfer-reaction study using the Super-Enge Split-Pole Spectrograph (SE-SPS) at the Fox Accelerator Laboratory at Florida State University. Proton and alpha decays were collected by the Silicon Array for Branching Ratio Experiments (SABRE) in coincidence with the triton reaction products detected at the focal plane. Proton asymptotic normalization coefficients were derived from ab initio symmetry-adapted no-core shell model proton-18F wavefunctions for relevant s-wave resonances. The properties of several s-wave states in 19Ne will be presented, along with their effects on the 18F(p,alpha)15O reaction rate.

Speaker: Khang Pham (Texas A&M University)

27 Studying Explosive Stellar Nucleosynthesis through (α,n) and (p,n) Reactions with SECAR

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

A new technique has been developed for direct measurements of both (α,n) and (p,n) reactions in inverse kinematics with SECAR (SEparator for CApture Reactions). Despite it being primarily designed for capture reactions, the development of machine learning-assisted ion-optics rendered the study of (p,n) reactions using a separator feasible, and a
$^{58}$Fe(p,n) measurement served as proof-of-principle for the method. Additionally, SECAR’s capabilities have been expanded to include (α,n) reaction measurements, as demonstrated in an initial case study of the $^{86}$Kr(α,n) reaction, which influences α-process nucleosynthesis and the elemental abundances observed in metal-poor stars.

In this talk, I will present recent (α,n) and (p,n) reaction measurements with SECAR, highlighting the experimental advancements that enabled these studies along with their astrophysical significance. These reaction studies pave the way for future direct reaction rate measurements on short-lived nuclei, which are essential for improving our understanding of heavy-element nucleosynthesis.

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

10:20 Coffee Break

Morning II

28 Uncertainties in the s-Process Nucleosynthesis of K-40 in Low-Mass AGB Stars and Implications for Exoplanets

We investigate the production of the long-lived radioactive isotope K-40
in low-mass asymptotic giant branch (AGB) stars, with a focus on quantifying
the impact of stellar model and nuclear physics uncertainties. Potassium-40 is
a key contributor to radiogenic heating in terrestrial planets,
yet its stellar origin and galactic evolution remain insufficiently well constrained.
Using a set of AGB stellar models spanning a range of masses and metallicities, we examine how variations in convective boundary mixing, mass loss,
and thermal pulse properties influence the synthesis and surface enrichment of
potassium isotopes. In parallel, we assess the sensitivity of K-40 production
to uncertainties in relevant neutron-capture reaction rates along the s-process path,
particularly in the vicinity of argon and potassium isotopes.
Our results will identify the dominant sources of uncertainty affecting K-40 yields
and provide revised estimates of its production in low-mass AGB stars.
We discuss the implications for galactic chemical evolution models and evaluate
the potential contribution of AGB stars to the inventory of radiogenic isotopes
incorporated into exoplanetary systems. These findings will offer new constraints
on the role of stellar nucleosynthesis in setting the internal heat budgets
and long-term geophysical evolution of rocky exoplanets.

Speaker: Pavel Denisenkov (University of Victoria)

29 Preparation for isotope measurements of presolar graphite, silicates, and oxides

Presolar grains help us to study the complex system of dying stars through their isotopic signatures. One important concept presolar grains help us explore is the neutron density and temperature of ejected material from AGB stars through measurements of isotopes impacted by s-process branching [1]. However, getting these grains is no simple task. Orgueil, a CI chondrite, contains ~10 ppm presolar graphite [2], and Murchison, a CM chondrite, has a concentration of ~1 ppm for grains larger than 1 μm in size [3]. These abundances indicate that at least one grain >1 μm should be exposed at the surface of a 1 $mm^{2}$ polished section. Previous presolar grain research on Murchison and Orgueil often relied on a chemical separation method to extract presolar graphite grains from their matrix [3, 4]. Although this method is helpful for concentrating presolar grains, it destroys the material surrounding the grains and thus removes their petrographic context. Furthermore, CI and CM chondrites are some of the least abundant meteorite classes but have the highest concentrations of presolar grains [2, 3]. Thus, using nondestructive techniques for presolar grain identification, like Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS), allows us to capitalize on the large abundance of presolar grains in CI and CM material without their destruction. These techniques can also be used for asteroid samples from Ryugu and Bennu, which have similar presolar graphite abundances as CI meteorites [5, 6]. More than 100 $mm^{2}$ each of polished sections of the Orgueil and Murchison meteorites have been imaged and chemically analyzed using SEM and EDS. From these images and chemical maps, hundreds of carbon-rich objects have been identified and documented. Following identification, closer SEM imaging revealed that many objects appear to be epoxy-filled holes or organic matter. A few of the identified carbon-rich objects show similarities to SEM images taken of separated presolar graphite grains. Isotope measurements of the elements Mo, Zr, Sr, and Ti using the Chicago Instrument for Laser Ionization (CHILI) [7] are planned to help us better constrain s-process branching points.
Silicates and oxides are also important types of presolar grains. One formation environment of such grains is early in the AGB thermal pulsing sequence when the envelope still has a C/O < 1 [8]. Isotope analysis of elements heavier than iron has yet to be measured in presolar silicates and oxides. Thus, nucleosynthetic signatures of these grains are not fully constrained, leaving many open questions concerning the early stages of AGB stars or other oxygen-rich stellar environments where these grains may have formed. To achieve the goal of measuring these elements (Mo, Zr, Sr, and Ti) in presolar silicates and oxides, previous measurement techniques must first be modified, as these phases are transparent to the nanosecond UV laser we have used for presolar SiC and graphite [7]. We are optimizing CHILI’s femtosecond ablation laser wavelength, pulse length, power, and timing to allow accurate isotopic measurements of optically transparent presolar grains.

[1] Busso M. et al. (1999) Annu. Rev. Astron. Astrophys. 37, 239–309. [2] Huss G. R. and Lewis R. S. (1995) Geochim. Cosmochim. Acta 59, 115–160. [3] Amari S. et al. (2014) Geochim. Cosmochim. Acta 133, 479–522. [4] Jadhav M. et al. (2013) Geochim. Cosmochim. Acta 113, 192–224. [5] Barnes J. J. et al. (2025) Nat. Astron. 9, 1785–1802. [6] Nguyen A. N. et al. (2023) Sci. Adv. 9, 28. [7] Stephan T. et al. (2016) Int. J. Mass Spectrom. 407, 1–15. [8] Nittler L. R. et al. (2008) Astrophys. J. 682, 1450–1478.

Speaker: Gavin Fowler (University of Chicago)

Saturday 30 May

Morning I

30 Availability of fast radioactive beams at FRIB for nuclear astrophysics

Nuclear reactions frequently involve radioactive species as one or both components in explosive astrophysical scenarios, such as (super)novae, Type I X-ray bursts, and neutron star mergers.  The reaction rates involved in calculating the astronomical observables are frequently unknown or poorly constrained in the Gamow window, requiring both direct and indirect measurements with both stable and rare isotope beams.  The Facility for Rare Isotope Beams (FRIB) is a new, cutting edge accelerator complex hosted at Michigan State University.  FRIB is designed to meet user needs, providing some of the most intense rare isotope beams to experimentalists from around the globe.  Most of the rare beams are produced onsite using the Advanced Rare Isotope Separator (ARIS) either via projectile fragmentation or in-flight fission.  ARIS produces unique beams for each experiment, including tailor-made intensity, purity, and energy suited to the users' requests up to our present capabilities.  The FRIB linac presently produces beams up to 20 kW, and we recently successfully performed tests at 30 kW, with the final goal of 400 kW.  The primary beam energies are typically in the 100-300 MeV/u range and impinge on mm-thick, rotating graphite target.  FRIB has a large, growing list of primary beams available to support new requests for intense secondary beams, which can be utilized in indirect measurements at energies above the Gamow window, or the species from ARIS can be stopped and re-accelerated for direct measurements.  The presentation will focus on how the ARIS team calculates, produces, and quantifies rare isotope beams for nuclear astrophysics experiments.

Speaker: Dr Daid Kahl (FRIB)

31 From Measured Cross Sections to Stellar Reaction Rates: Quantifying Active-Target Measurement Uncertainties

Nuclear reaction rates in stars are determined from the folding of the Maxwell Boltzmann distribution with the reaction cross section. The latter quantity describes the likelihood of interaction of two particles at a particular energy. One of the main roles of nuclear physics in the field of nuclear astrophysics is to provide information about these cross sections.
There are many direct and indirect ways to determine these cross sections experimentally. One of the most influential types of direct measurements is the active-target technique. This technique involves using a gas-filled detector in which the detection medium is also the target. While powerful, they come with some drawbacks intrinsic to their design. First, the total beam intensity that can be delivered to these experiments is limited due to the ionization within the gas detector-target. Second, these measurements have an energy resolution which is much larger than the energy scales of the resonances which are typically found in these cross sections. This can result in the loss of critical information due to the limited energy resolution.
The typical approach has been to measure the cross section at higher energies and then to extrapolate that cross section using a statistical Hauser-Feshbach code, such as TALYS, at lower energies. These extrapolations are then used to determine the reaction rates in the astrophysical region of interest. There are uncertainties which come from this approach, but these are not well quantified. Understanding the relationship between the energy resolution and the inferred reaction rate is critical in design of successful future experimental apparatus.
We aim to provide a computational framework for assessing the uncertainties which arise from these thick-target active-target measurements, and to compute expected uncertainties due to energy resolution effects.

Speaker: Chirag Rathi (Texas A&M University)

32 In situ isotopic analysis of presolar graphite grains challenge AGB star models

We have measured carbon, nitrogen, zirconium, molybdenum, and barium isotopes in two large presolar graphite grains found in situ in sections of the CM2 carbonaceous chondrites Murchison and Maribo. Carbon and nitrogen were analyzed using nanometer-scale secondary ion mass spectrometry (NanoSIMS), and heavy elements were measured by resonance ionization mass spectrometry (RIMS) with the Chicago Instrument for Laser ionization (CHILI) [1].
The grain from Maribo showed nearly pure s-process molybdenum in a subgrain, probably a refractory carbide, also containing highly enriched s-process zirconium. The Murchison grain is enriched in s-process molybdenum and zirconium as well. Barium concentrations in both grains are low, but isotopic ratios consistent with the s-process were also observed. Both grains show significant enrichments in $^{13}$C, while nitrogen isotope ratios are close to the terrestrial value.
These findings are consistent with condensation in the outflows of low-mass, low-metallicity asymptotic giant branch (AGB) stars. However, the observation of nearly pure s-process molybdenum in the Maribo grain is inconsistent with current AGB star models [3–5]. Similar enrichments in s-process ruthenium, also outside the range of such models, have been observed in a graphite grain extracted from Murchison [2]. All these AGB star models assume homogenization of s-process material in the convective stellar envelope after each third dredge-up (TDU) episode, and prior to grain condensation. One explanation for our findings is that these grains formed in isotopically inhomogeneous regions, high-density clumps, arising during TDU events, as has been suggested before [6]. Another option could be a very late thermal pulse from a post-AGB star [7].
Furthermore, neutron capture at $^{95}$Zr, an important s-process branch point, was only marginally activated for our grains, further challenging the stellar models and theoretically derived $^{95}$Zr neutron-capture cross sections.
Improved stellar nucleosynthesis models should take these new observations from presolar grains into account. Published isotope data of presolar silicon carbide and graphite grains are compiled in the Presolar Grain Database [8, 9] (latest versions available at https://zenodo.org/doi/10.5281/zenodo.8187219 and
https://zenodo.org/doi/10.5281/zenodo.11188115).

[1] Stephan T. et al. (2016) Int. J. Mass Spectrom. 407, 1–15. [2] Stephan T. et al. (2026) Eur. Phys. J. A 62, 47. [3] Cristallo S. et al. (2011) Astrophys. J. Suppl. Ser. 197, 17. [4] Cristallo S. et al. (2015) Astrophys. J. Suppl. Ser. 219, 40. [5] Szányi B. et al. (2025) Astron. Astrophys. 697, A48. [6] Croat T. K. et al. (2005) Astrophys. J. 631, 976–987. [7] Jadhav M. et al. (2013) Astrophys. J. Lett. 777, L27. [8] Stephan T. et al. (2024) Astrophys. J. Suppl. Ser. 270, 27. [9] Stephan T. et al. (2024) Meteorit. Planet. Sci. 59, A399 (#6388).

Speaker: Thomas Stephan (University of Chicago)

10:20 Closing Remarks