First Exploration of Neutron Shell Structure below Lead and beyond N = 126
Not Available
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
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First Direct Measurement of Mg (α,p) 25 Al and Implications for X-Ray Burst Model-Observation Comparisons
Type-I x-ray bursts can reveal the properties of an accreting neutron star system when compared with astrophysics model calculations. However, model results are sensitive to a handful of uncertain nuclear reaction rates, such as 22 Mg(α , p). We report the first direct measurement of 22 Mg(α , p), performed with the Active Target Time Projection Chamber. The corresponding astrophysical reaction rate is orders of magnitude larger than determined from a previous indirect measurement in a broad temperature range. Overall, our new measurement suggests a less-compact neutron star in the source GS1826-24.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Experimental study of the 24 Na m ( d,p ) 25 Na reaction and implications for the influence of the 24 Al m isomer on rp -process nucleosynthesis
A radioactive beam of 24 Na with 90% of its content in its 1 + isomeric state (E ex = 0.472 MeV, t 1/2 = 20.18 ms) has been developed and used to perform a measurement of the 24 Na m ( d,p ) 25 Na reaction at the John D. Fox Accelerator Laboratory at Florida State University. This reaction selectively populated ℓ = 0 transfers, allowing the study of low-spin states in 25 Na. Mirror symmetry arguments were then used to investigate the effects of the isomeric state of 24 Al (E ex = 0.426 MeV, t 1/2 = 130 ms) on the astrophysical rate of the 24 Al m (p,γ) 25 Si reaction. Experimental parameters were extracted to provide, for the first time, an experimental reaction rate for the destruction of 24 Al via proton captures in its isomeric state relevant to rp-process nucleosynthesis.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Near-threshold resonances in C 11 and the B 10 ( p , α ) Be 7 aneutronic reaction
The nucleus 11 C plays an important role in the boron-proton fusion reactor environment as a catalyzer of the 10 B(p,α) 7 Be reaction which, by producing a long-lived isotope of 7 Be, poisons the aneutronic fusion process 11 B(p,2α) 4 He. The low-energy cross section of 10 B(p,α) 7 Be depends on the near-threshold states 7/2$^{+}_{1}$, 5/2$^{+}_{2}$, 5/2$^{+}_{3}$ in 11 C whose properties are primarily known from the indirect measurements. Here we investigate the continuum-coupling induced collectivization of these resonances in the shell model embedded in the continuum. We predict a significant enhancement of the 10 B(p,α) 7 Be cross section at energies accessible to the laser-driven hot plasma facilities.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Cross-section measurements to low-lying excited final states in the 24 M(α,p) 27 Al*(γ) reaction as an energy source for x-ray bursts
Energy production in Type Ia x-ray bursts depends on a number of nuclear reactions that become efficient in a hot environment (up to 2 GK). Model sensitivity studies have been performed in an effort to better identify the reactions that have the largest effect, but these efforts are hampered by the high level of complexity of the astrophysical model and large nuclear physics uncertainties. In a recent study, the 24 Mg(α,p) 27 Al reaction was found to significantly affect the energy generation in x-ray bursts. This manuscript reports the first study of the 24 Mg(α,p 1,2 γ) 27 Al reaction at energies relevant for x-ray bursts. In conclusion, the branches to the 27 Al excited states increase to a small degree the estimates of the total astrophysical 24 Mg(α,p) 27 Al reaction rate.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Framework for phase transitions between the Maxwell and Gibbs constructions at finite temperature
The characteristics of the hadron-to-quark first-order phase transition differ depending on whether charge neutrality is locally or globally fulfilled. In 𝛽-equilibrated matter, these two possibilities correspond to the Maxwell and Gibbs constructions. Recently, we presented a new framework in which a continuously varying parameter allows one to describe a first-order phase transition in intermediate scenarios to the two extremes of fully local and fully global charge neutrality. In this work, we extend the previous framework to finite temperatures and out-of-𝛽 equilibrium conditions, making it available for simulations of core-collapse supernovae and binary neutron star mergers. We investigate its impact on key thermodynamic quantities across a range of baryon densities, temperatures, and electron fractions. We find that when matter is not in 𝛽 equilibrium, the pressure in the mixed phase is not constant even for the case of fully local charge neutrality. Moreover, we compute the thermal index using three different approaches, demonstrating that the finite-temperature extension of an equation of state using a constant thermal index can be ill defined when applied to the mixed phase.
QCD phase transitions↗
Radius and equation of state constraints from massive neutron stars and GW190814
Motivated by the unknown nature of the 2.50–2.67M⊙ compact object in the binary merger event GW190814, we study the maximum neutron star mass based on constraints from low-energy nuclear physics, neutron star tidal deformabilities from GW170817, and simultaneous mass-radius measurements of PSR J0030+045 from NICER. Our prior distribution is based on a combination of nuclear modeling valid in the vicinity of normal nuclear densities together with the assumption of a maximally stiff equation of state at high densities, a choice that enables us to probe the connection between observed heavy neutron stars and the transition density at which conventional nuclear physics models must break down. Here we demonstrate that a modification of the highly uncertain suprasaturation density equation of state beyond 2.64 times normal nuclear density is required in order for chiral effective field theory models to be consistent with current neutron star observations and the existence of 2.6M⊙ neutron stars. We also show that the existence of very massive neutron stars strongly impacts the radii of ≈ 2.0M⊙ neutron stars (but not necessarily the radii of 1.4 M⊙ neutron stars), which further motivates future NICER radius measurements of PSR J1614 – 2230 and PSR J0740+6620.
79 ASTRONOMY AND ASTROPHYSICS↗
Improved nuclear physics near A = 61 refines urca neutrino luminosities in accreted neutron star crusts
We performed Penning trap mass measurements for 61 Zn at the National Superconducting Cyclotron Laboratory and NuShellX calculations of the 61 Zn and 62 Ga structure using the GXPF1A Hamiltonian to obtain improved estimates of the 61 Zn(p,γ) 62 Ga and 60 Cu(p,γ) 61 Zn reaction rates. Surveying astrophysical conditions for type-I x-ray bursts with the code mesa, implementing our improved reaction rates, and taking into account updated nuclear masses for 61 V and 61 Cr from the recent literature, we refine the neutrino luminosity from the important mass number A = 61 urca cooling source in accreted neutron-star crusts. Furthermore, this improves our understanding of the thermal barrier between deep heating in the crust and the shallow depths where extra heat is needed to explain x-ray superbursts, as well as the expected signature of crust urca neutrino emission in light curves of cooling transients
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Chiral effective field theory calculation of neutrino reactions in warm neutron-rich matter
Neutrino scattering and absorption rates of relevance to supernovae and neutron star mergers are obtained from nuclear matter dynamical structure functions that encode many-body effects from nuclear mean fields and correlations. In this study, we employ nuclear interactions from chiral effective field theory to calculate the density, spin, isospin, and spin-isospin response functions of warm β-equilibrium nuclear matter. We include corrections to the single-particle energies in the mean field approximation as well as vertex corrections resummed in the random phase approximation (RPA), including both direct and exchange diagrams. We find that correlations included through the RPA redistribute the strength of the response to higher energy for neutrino absorption and lower energy for antineutrino absorption. This tends to suppress the absorption rate of electron neutrinos across all relevant energy scales. In contrast, the inclusion of RPA correlations enhances the electron antineutrino absorption rate at low energy and suppresses the rate at high energy. These effects are especially important at high-density and in the vicinity of the neutrino decoupling region. Implications for heavy element nucleosynthesis, electromagnetic signatures of compact object mergers, supernova dynamics, and neutrino detection from galactic supernovae are discussed briefly.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Observable signatures of enhanced axion emission from protoneutron stars
Here we perform general relativistic one-dimensional supernova (SN) simulations to identify observable signatures of enhanced axion emission from the pion-induced reaction π - + p →n + a inside a newly born protoneutron star (PNS). We focus on the early evolution after the onset of the supernova explosion to predict the temporal and spectral features of the neutrino and axion emission during the first 10 s. Pions are included as explicit new degrees of freedom in hot and dense matter. Their thermal population and their role in axion production are both determined consistently to include effects due to their interactions with nucleons. For a wide range of ambient conditions encountered inside a PNS, we find that the pion-induced axion production dominates over nucleon-nucleon bremsstrahlung processes. By consistently including the role of pions on the dense matter equation of state and on the energy loss, our simulations predict robust discernible features of neutrino and axion emission from a galactic supernova that can be observed in terrestrial detectors. For axion couplings that are compatible with current bounds, we find a significant suppression with time of the neutrino luminosity during the first 10 s. This suggests that current bounds derived from the neutrino signal from SN 1987A can be improved and that future galactic supernovae may provide significantly more stringent constraints.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Detectability of QCD phase transitions in binary neutron star mergers: Bayesian inference with the next generation gravitational wave detectors
We study the detectability of postmerger QCD phase transitions in neutron star binaries with next-generation gravitational-wave detectors Cosmic Explorer and Einstein Telescope. We perform numerical relativity simulations of neutron star mergers with equations of state that include a quark deconfinement phase transition through either a Gibbs or Maxwell construction. These are followed by Bayesian parameter estimation of the associated gravitational-wave signals using the nrpmw waveform model, with priors inferred from the analysis of the inspiral signal. We assess the ability of the model to measure the postmerger peak frequency $f$$^{peak}_{2}$ and identify aspects that should be improved in the model. We show that, even at postmerger signal to noise ratios as low as 10, the model can distinguish (at the 90% level) $f$$^{peak}_{2}$ between binaries with and without a phase transition in most cases. Phase-transition induced deviations in the $f$$^{peak}_{2}$ from the predictions of equation-of-state insensitive relations can also be detected if they exceed 1.6σ. Our results suggest that next-generation gravitational wave detectors can measure phase transition effects in binary neutron star mergers. Furthermore, unless the phase transition is “strong,” disentangling it from other hadronic physics uncertainties will require significant theory improvements.
79 ASTRONOMY AND ASTROPHYSICS↗
Open-source library for performance-portable neutrino reaction rates: Application to neutron star mergers
A realistic and detailed description of neutrinos in binary neutron star (BNS) mergers is essential to build reliable models of such systems. To this end, we present bns_nurates, a novel open-source numerical library designed for the efficient on-the-fly computation of neutrino interactions, with particular focus on regimes relevant to BNS mergers. bns_nurates targets a higher level of accuracy and realism in the implementation of commonly employed reactions by accounting for relevant microphysics effects on the interactions, such as weak magnetism and mean field effects. It also includes the contributions of inelastic neutrino scattering off electrons and positrons and (inverse) nucleon decays. Finally, it offers a way to reconstruct the neutrino distribution function in the framework of moment-based transport schemes. As a first application, we compute both energy-dependent and energy-integrated neutrino emissivities and opacities for conditions extracted from a BNS merger simulation with m1 transport scheme. We find some qualitative differences in the results when considering the impact of the additional relevant reactions and of microphysics effects. For example, neutrino-electron/positron scattering reactions are important for the energy exchange of heavy-type neutrinos as they do not undergo semileptonic charged-current processes, when μ± are not accounted for. Moreover, weak magnetism and mean field effects can significantly modify the contribution of β processes for electron-type (anti)neutrinos, increasing at the same time the importance of (inverse) neutron decays. Here, the improved treatment for the reaction rates also modifies the conditions at which neutrinos decouple from matter in the system, potentially affecting their emission spectra.
79 ASTRONOMY AND ASTROPHYSICS↗
Actinide Crystallization and Fission Reactions in Cooling White Dwarf Stars
The first solids that form as a cooling white dwarf (WD) starts to crystallize are expected to be greatly enriched in actinides. This is because the melting points of WD matter scale as Z5/3 and actinides have the largest charge Z. We estimate that the solids may be so enriched in actinides that they could support a fission chain reaction. This reaction could ignite carbon burning and lead to the explosion of an isolated WD in a thermonuclear supernova (SN Ia). Our mechanism could potentially explain SN Ia with sub-Chandrasekhar ejecta masses and short delay times.
79 ASTRONOMY AND ASTROPHYSICS↗
Normalizing Flows for Microscopic Many-Body Calculations: An Application to the Nuclear Equation of State
We report that normalizing flows are a class of machine learning models used to construct a complex distribution through a bijective mapping of a simple base distribution. We demonstrate that normalizing flows are particularly well suited as a Monte Carlo integration framework for quantum many-body calculations that require the repeated evaluation of high-dimensional integrals across smoothly varying integrands and integration regions. As an example, we consider the finite-temperature nuclear equation of state. An important advantage of normalizing flows is the ability to build highly expressive models of the target integrand, which we demonstrate enables precise evaluations of the nuclear free energy and its derivatives. Furthermore, we show that a normalizing flow model trained on one target integrand can be used to efficiently calculate related integrals when the temperature, density, or nuclear force is varied. This work will support future efforts to build microscopic equations of state for numerical simulations of supernovae and neutron star mergers that employ state-of-the-art nuclear forces and many-body methods.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Probing the Incompressibility of Nuclear Matter at Ultrahigh Density through the Prompt Collapse of Asymmetric Neutron Star Binaries
Using 250 neutron star merger simulations with microphysics, we explore for the first time the role of nuclear incompressibility in the prompt collapse threshold for binaries with different mass ratios. We demonstrate that observations of prompt collapse thresholds, either from binaries with two different mass ratios or with one mass ratio but combined with the knowledge of the maximum neutron star mass or compactness, will constrain the incompressibility at the maximum neutron star density K max to within tens of percent. This otherwise inaccessible measure of K max can potentially reveal the presence of hyperons or quarks inside neutron stars.
79 ASTRONOMY AND ASTROPHYSICS↗
Structure Factors for Hot Neutron Matter from Ab Initio Lattice Simulations with High-Fidelity Chiral Interactions
We present the first ab initio lattice calculations of spin and density correlations in hot neutron matter using high-fidelity interactions at next-to-next-to-next-to-leading order in chiral effective field theory. These correlations have a large impact on neutrino heating and shock revival in core-collapse supernovae and are encapsulated in functions called structure factors. Unfortunately, calculations of structure factors using high-fidelity chiral interactions were well out of reach using existing computational methods. In this Letter, we solve the problem using a computational approach called the rank-one operator (RO) method. The RO method is a general technique with broad applications to simulations of fermionic many-body systems. It solves the problem of exponential scaling of computational effort when using perturbation theory for higher-body operators and higher-order corrections. Using the RO method, we compute the vector and axial static structure factors for hot neutron matter as a function of temperature and density. Here, the ab initio lattice results are in good agreement with virial expansion calculations at low densities but are more reliable at higher densities. Random phase approximation codes used to estimate neutrino opacity in core-collapse supernovae simulations can now be calibrated with ab initio lattice calculations.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Surrogate light curve models for kilonovae with comprehensive wind ejecta outflows and parameter estimation for AT2017gfo
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Iron-rich microstructure records of high temperature multi-component silicate melt behavior in nuclear fallout
Above-ground nuclear explosions that interact with the surface of the earth entrain materials from the surrounding environment, influencing the resulting physical and chemical evolution of the fireball, which can affect the final chemical phase and mobility of hazardous radionuclides that are dispersed in the environment as fallout particles. The interaction of iron with a nuclear explosion is of specific interest due to the potential for iron to act as a redox buffer and because of the likelihood of significant masses of metals to be present in urban environments. We investigated fallout from a historic surface interacting nuclear explosion conducted on a steel tower and report the discovery of widespread and diverse iron-rich micro-structures preserved within the samples, including crystalline dendrites and micron-scale iron-rich spheres with liquid immiscibility textures. We assert these micro-structures reflect local redox conditions and cooling rates and can inform interpretation of high temperature events, enabling new insights into fireball condensation physics and chemistry when metals from the local environment (i.e. structural steel) are vaporized or entrained. Finally, these observations also significantly expand the availability of silicate immiscibility datasets applicable to rapidly quenched systems such as meteorite impact melt glass.
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗