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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Progenitors and explosion properties of supernova remnants hosting central compact objects: II. A global systematic study with a comparison to nucleosynthesis models

ABSTRACT Core-collapse explosions of massive stars leave behind neutron stars, with a known diversity that includes the ‘Central Compact Objects’ (CCOs). Typified by the neutron star discovered near the centre of the Cas A supernova remnant (SNR), CCOs have been observed to shine only in X-rays. To address their supernova progenitors, we perform a systematic study of SNRs that contain a CCO and display X-ray emission from their shock-heated ejecta. We make use of X-ray data primarily using the Chandra X-ray observatory, complemented with XMM–Newton. This study uses a systematic approach to the analysis of each SNR aimed at addressing the supernova progenitor as well as the explosion properties (energy and ambient density). After fitting for the ejecta abundances estimated from a spatially resolved spectroscopic study, we compare the data to six nucleosynthesis models making predictions on supernova ejecta yields in core-collapse explosions. We find that the explosion models commonly used by the astrophysics community do not match the ejecta yields for any of the SNRs, suggesting additional physics, for example multidimensional explosion models or updated progenitor structures, are required. Overall we find low-mass (≤25 solar masses) progenitors among the massive stars population and low-energy explosions (<1051 ergs). We discuss degeneracies in our model fitting, particularly how altering the explosion energy affects the estimate of the progenitor mass. Our systematic study highlights the need for improving on the theoretical models for nucleosynthesis predictions as well as for sensitive, high-resolution spectroscopy observations to be acquired with next generation X-ray missions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Mass measurements of 60–63 Ga reduce x-ray burst model uncertainties and extend the evaluated T=1 isobaric multiplet mass equation

We report precision mass measurements of neutron-deficient gallium isotopes approaching the proton drip line. The measurements of 60–63 Ga performed with the TITAN multiple-reflection time-of-flight mass spectrometer provide a more than threefold improvement over the current literature mass uncertainty of 61 Ga and mark the first direct mass measurement of 60 Ga. The improved precision of the 61 Ga mass has important implications for the astrophysical rp process, as it constrains essential reaction Q values near the 60 Zn waiting point. Based on calculations with a one-zone model, we demonstrate the impact of the improved mass data on prediction uncertainties of x-ray burst models. The first-time measurement of the 60 Ga ground-state mass establishes the proton-bound nature of this nuclide, thus constraining the location of the proton drip line along this isotopic chain. Including the measured mass of 60 Ga further enables us to extend the evaluated T = 1 isobaric multiplet mass equation up to A = 60.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Nuclear fission reaction simulations in compact stars

Type-Ia supernovas are powerful stellar explosions that provide important distance indicators in cosmology. Recently, we proposed a new Type-Ia supernova mechanism that involves a nuclear fission chain-reaction in an isolated white dwarf [Phys. Rev. Lett. 126, 131101 (2021)]. Here, in this work, we perform novel reaction network simulations of the actinide-rich first solids in a cooling white dwarf. The network includes neutron-capture and fission reactions on a range of U and Th isotopes with various possible values for 235 U enrichment. We find, for modest 235 U enrichments, neutron capture on 238 U and 232 Th can breed additional fissile nuclei so that a significant fraction of all U and Th nuclei may fission during the chain reaction. Finally, we compute the energy release from the fission chain reaction for various uranium enrichments; a novel result that is a necessary input for thermal diffusion simulations of carbon ignition.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Investigation of 31 P levels near the proton threshold with nuclear resonance fluorescence and the impact on the 30 Si (𝑝,𝛾)⁢ 31 P thermonuclear rate

We investigated the nuclear structure of 31 P near the proton threshold using nuclear resonance fluorescence (NRF) to refine the properties of key resonances in the 30 Si (𝑝,𝛾)⁢ 31 P reaction, which is critical for nucleosynthesis in stellar environments. Excitation energies and spin-parities were determined for several states, including two unobserved resonances at 𝐸 𝑟 = 18.7keV and 𝐸 𝑟 = 50.5keV. The angular correlation analysis enabled the first unambiguous determination of the orbital angular momentum transfer for these states. These results provide a significant update to the 30 Si (𝑝,𝛾)⁢ 31 P thermonuclear reaction rate, with direct implications for models of nucleosynthesis in globular clusters and other astrophysical sites. The revised rate is substantially lower than previous estimates at temperatures below 200 MK, affecting predictions for silicon isotopic abundances in stellar environments. Furthermore, our work demonstrates the power of NRF in constraining nuclear properties, and provides a framework for future studies of low-energy resonances relevant to astrophysical reaction rates.

20 ≤ A ≤ 38↗
DOE OSTI2024

Mass measurements of neutron-rich nuclei near $N = 70$

The astrophysical origin for the chemical elements between the first and second r-process peaks is a matter of intense debate, with a number of nucleosynthesis processes at explosive stellar environments possibly contributing to their production. Reliable data on the trends of neutron separation energies of neutron-rich isotopes are required to model neutron-capture processes that would produce these elements. Masses of 104 Y, 106 Zr, 112 Mo, and 115 Tc have been measured with the time-of-flight-magnetic-rigidity (ToF–Bρ) technique at the National Superconducting Cyclotron Laboratory at Michigan State University. The experiment is the first application of the ToF–Bρ technique at the S800 spectrograph that reached the mass region relevant to heavy-element nucleosynthesis. Finally, the two-neutron separation energy deduced from the measured masses exhibits a smooth trend consistent with the theoretical predictions within the range of experimental uncertainty, indicating that there is no sudden shape transition in these isotopes as hinted at by previous data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

SECAR: A recoil separator for nuclear astrophysics

Proton-and alpha-capture reactions on unstable proton-rich nuclei power astrophysical explosions like novae and X-ray bursts. Direct measurements of these reactions are crucial for understanding the mechanisms behind these explosions and the nucleosynthesis at such sites. The recoil mass separator, SECAR (SEparator for CApture Reactions) at the National Superconducting Cyclotron Laboratory (NSCL) and the Facility for Rare Isotope Beams (FRIB), has been designed with the required sensitivity to study (p,γ) and (α,γ) reactions, directly at astrophysical energies in inverse kinematics, with radioactive beams of masses up to about A = 65. The complete SECAR system, including two Wien Filters for high mass resolution, has been installed at Michigan State University and is currently being commissioned. The present article introduces the SECAR concept, its scientific goals, and provides an update of the current status of the project.

Tsintari, P↗
DOE OSTI2024

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↗
DOE OSTI2026

Exploring composition mixing in kilonova ejecta with ray-by-ray simulations

Binary neutron star merger (BNSM) ejecta are considered a primary repository of r-process nucleosynthesis and a source of the observed heavy-element abundances. We implement composition mixing into ray-by-ray radiation-hydrodynamic simulations of BNSM ejecta, coupled with an online nuclear network (NN). We model mixing via a gradient-based mixing approximation that evolves simultaneously with the hydrodynamics. Here, we find that mixing occurs in regions where the electron fraction changes rapidly. While mixing smooths composition gradients in transition regions, it has a negligible impact on the heavy-element yields. This is because the primary r-process site (the equatorial ejecta) is initially homogeneous in free neutrons, leaving no strong gradients for mixing to act upon. In each angular ray, the abundances of the most produced elements are robust under mixing, while the less abundant ones are more affected. The total global abundances change only slightly from mixing, since each angular ray contributes its most abundant elements. Furthermore, the predicted kilonova light curves show only minor reddening, with differences below the detectability of state-of-the-art telescopes. In general, we do not observe significant effects from mixing in the time span of the r-process. Consequently, mixing only leads to minor variations in abundances and light curves in ray-by-ray simulations.

Explosive burning↗
DOE OSTI2023

Cross sections of the 83 Rb⁢(p,γ)⁢ 84 Sr and 84 Kr⁢(p,γ)⁢ 85 Rb reactions at energies characteristic of the astrophysical γ process

We have measured the cross section of the Rb 83 ( p , γ ) Sr 84 radiative capture reaction in inverse kinematics using a radioactive beam of Rb 83 at incident energies of 2.4 and 2.7 A MeV. Prior to the radioactive beam measurement, the Kr 84 ( p , γ ) Rb 85 radiative capture reaction was measured in inverse kinematics using a stable beam of Kr 84 at an incident energy of 2.7 A MeV. The effective relative kinetic energies of these measurements lie within the relevant energy window for the γ process in supernovae. The central values of the measured partial cross sections of both reactions were found to be 0.17 – 0.42 times the predictions of statistical model calculations. Assuming the predicted cross section at other energies is reduced by the same factor leads to a slightly higher calculated abundance of the p nucleus Sr 84 , caused by the reduced rate of the Sr 84 ( γ , p ) Rb 83 reaction derived from the present measurement.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Developing the S 32 ( p , d ) S * 31 ( p ) ( γ ) reaction to probe the P 30 ( p , γ ) S 31 reaction rate in classical novae

Background: The 30 P(p,γ) 31 S reaction rate is one of the largest remaining sources of uncertainty in the final abundances of nuclei created in a classical nova involving a ONe white dwarf. The reaction rate directly influences silicon isotopic ratios, which are used as identifiers of presolar grains with nova origins. Additionally, the uncertainty in the 30 P(p,γ) 31 S reaction rate has been found to limit the use of nova nuclear thermometers based on observations of elemental ratios in nova ejecta. Purpose: Reduce uncertainties in the nuclear data for proton-unbound states in 31 S, which act as resonances for the 30 P(p,γ) 31 S reaction at classical nova temperatures, and develop a technique for high efficiency, high-resolution reaction-decay coincidence measurements. Methods: Here, the 32 S(p,d) 31 S reaction was used to populate the states of interest in 31 S. The experiment was performed at the Texas A&M Cyclotron Institute using the LLNL Hyperion array for the detection of charged particles and γ rays. A downstream silicon telescope was used to select reaction deuterons, and a single upstream silicon detector was used to measure protons emitted in the decay of unbound 31 S levels. Results: Several states in 31 S above the proton separation energy were observed to have been populated. Decay protons from the resonant states in 31 S were identified as events in the upstream silicon detectors that came in coincidence with deuterons in the downstream telescope. Protons emitted from these states were measured and branching ratios extracted. Conclusions: While no new reaction rate is derived, spin-parity assignments for several higher-lying proton unbound states have been confirmed. Measured p 0 branching ratios for these levels have been compared to previous measurements with good agreement, and in some cases provided a reduction in uncertainty. The previously identified T = 3/2 state may have been incorrectly assigned a large p 0 branching ratio in a previous measurement. The technique of measuring reaction-decay coincidences with a particle-gamma setup appears promising.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

New constraints on the Al 25 ( p , γ ) reaction and its influence on the flux of cosmic γ rays from classical nova explosions

The astrophysical 25 Al(p,γ) 26 Si reaction represents one of the key remaining uncertainties in accurately modeling the abundance of radiogenic 26 Al ejected from classical novae. Specifically, the strengths of key proton-unbound resonances in 26 Si, that govern the rate of the 25 Al(p,γ) reaction under explosive astrophysical conditions, remain unsettled. Here, we present a detailed spectroscopy study of the 26 Si mirror nucleus 26 Mg. We have measured the lifetime of the 3 + , 6.125-MeV state in 26 Mg to be 19(3) fs and provide compelling evidence for the existence of a 1 – state in the T = 1, A = 26 system, indicating a previously unaccounted for ℓ = 1 resonance in the 25 Al(p,γ) reaction. Using the presently measured lifetime, together with the assumption that the likely 1 – state corresponds to a resonance in the 25 Al + p system at 435.7(53) keV, we find considerable differences in the 25 Al(p,γ) reaction rate compared to previous works. Furthermore, based on current nova models, we estimate that classical novae may be responsible for up to ≈ 15% of the observed galactic abundance of 26 Al.

20 ≤ A ≤ 38↗
DOE OSTI2020

Measurements of proton capture in the A=100–110 mass region: Constraints on the In 111 (γ,p)/(γ,n) branching point relevant to the γ process

The γ process is an explosive astrophysical scenario, which is thought to be the primary source of the rare proton-rich stable p nuclei. However, current γ-process models remain insufficient in describing the observed p-nuclei abundances, with disagreements up to two orders of magnitude. A sensitivity study has identified 111 In as a model-sensitive (γ,p)/(γ,n) branching point within the γ process. Constraining the involved reaction rates may have a significant impact on the predicted p-nuclei abundances. Here we report on measurements of the cross sections for 102 Pd (p,γ) 103 Ag, 108 Cd (p,γ) 109 In, and 110 Cd (p,γ) 111 In reactions for proton laboratory energies 3–8 MeV using the high efficiency total absorption spectrometer and the γ-summing technique. These measurements were used to constrain Hauser-Feshbach parameters used in talys 1.9, which constrains the 111 In(γ,p) 110 Cd and 111 In(γ,n) 110 Ag reaction rates. The newly constrained reaction rates indicate that the 111 In(γ,p)/(γ,n) branching point occurs at a temperature of 2.71 ± 0.05 GK, well within the temperature range relevant to the γ process. These findings differ significantly from previous studies and may impact the calculated abundances.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Constraining the Synthesis of the Lightest 𝑝 Nucleus 74 Se

We provide the first experimental cross section of the 73 As(p, γ) 74 Se reaction to constrain one of the main destruction mechanisms of the p nucleus 74 Se in explosive stellar environments. The measurement was done using a radioactive 73 As beam at incident energies of 3.1 and 3.7 MeV/nucleon. Along with the total cross section measurement, statistical properties of the 74 Se compound nucleus were extracted, constraining the reaction cross section across the entire Gamow window of the γ process. The impact of the experimentally constrained reaction rate on 74 Se production in Type II supernovae is investigated through Monte Carlo one-zone network simulations. The results indicate that the overproduction of 74 Se by Type II supernova models cannot be resolved by nuclear physics and point towards the description of the astrophysical conditions of the γ process.

59 ≤ A ≤ 89↗
DOE OSTI2025

Constraining nuclear mass models using 𝑟-process observables with multiobjective optimization

Modeling nuclear masses, particularly for nuclei far from stability, remains a key objective in nuclear physics. One contemporary approach is machine learning (ML), which trains on experimental data, but can suffer large errors when extrapolating toward neutron-rich species. In nature, such masses shape observables for the rapid neutron capture process (𝑟 process), which in principle could inform ML models. Here, we introduce a multiobjective optimization approach using the Pareto front algorithm. We show that this technique, capable of identifying models that generate 𝑟-process abundances aligning with both solar and stellar data, is a promising method to select ML models with reliable extrapolation power.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Gamma-ray signatures of 𝑟-process radioactivity from the collapse of magnetized white dwarfs

We predict the gamma-ray line emission from 𝑟-process nuclei synthesized in the ejecta of the accretion-induced collapse (AIC) of a magnetized, rapidly rotating white dwarf. Using ejecta from a two-dimensional general-relativistic neutrino-magnetohydrodynamic simulation, further evolved with a radiation-hydrodynamics code coupled to an in situ nuclear reaction network, we construct angle-dependent gamma-ray spectra in the 0.01–10 MeV band via composition-dependent ray tracing through the ejecta. The emission between ∼1 and 10 d is dominated by 132 I (𝑡 1/2 = 2.3 h), continuously replenished by the decay of its parent 132 Te (𝑡 1/2 = 3.2 d), with additional contributions from 131 I, 133 Xe, and 132 Te . At 𝑡 ≳ 20 d, 56 Co (from 56 Ni decay) becomes the primary emitter. The simultaneous presence of 𝑟 process and iron-peak gamma-ray lines is distinctive of AIC ejecta and absent in binary neutron star mergers, where iron-peak nuclei are generally not synthesized. Comparing with the 3⁢𝜎 continuum sensitivities of planned MeV gamma-ray telescopes (COSI, AMEGO-X, e-ASTROGAM, GRAMS, GammaTPC), we find the brightest 𝑟-process lines detectable to ∼10 Mpc by GammaTPC and GRAMS, with the signal approaching their sensitivity threshold at 30 Mpc. As a result, the 𝑟-process spectral features survive time integration over ∼30 d exposures, demonstrating robustness against the long observation times required by gamma-ray detectors.

Nuclear reactions↗
DOE OSTI2026

Direct cross section measurement of 102 Pd ⁢(𝛾,𝑝) and 102 Pd ⁢(𝛾,𝛼) for the astrophysical 𝑝 process

Background: A handful of neutron-deficient stable nuclei, known as the “p nuclei,” cannot be produced through astrophysical neutron capture processes. Instead, some of these nuclei are proposed to be produced by 𝛾-induced reactions on existing r- and s-process seeds. The specific astrophysical site or sites are not yet identified, however, with uncertainties in the cross sections of these 𝛾-induced reactions playing a role. Databases of reaction rates for astrophysical simulations often rely on theoretical statistical model calculations, such as Hauser-Feshbach, for rates where no experimental information is known. However, reasonable variations in the choice of parametrizations of various nuclear properties can create order-of-magnitude variations in the final predicted cross sections and reaction rates, which are then propagated through the models to the predicted final abundances. Purpose: To better constrain these statistical model calculations and ultimately reduce the uncertainties from the nuclear physics on our understanding of the p nuclei, a measurement of the cross sections of 𝛾-induced reactions on the p-nucleus 102 Pd was undertaken. This work represents the first measurement of its kind, using segmented silicon detectors to measure prompt charged particle emission from 𝛾-induced reactions. Methods: Quasimonoenergetic gamma beams from the High Intensity 𝛾 Source facility bombarded an enriched 102 Pd target. A segmented silicon array was arranged to detect the particles emitted from (𝛾,𝑝) and (𝛾,𝛼) reactions. Results: Reaction cross sections were deduced at multiple 𝛾-beam energies between 10 and 19 MeV, and compared to statistical model calculations using talys-1.96. The 102 Pd ⁢(𝛾,𝑝)⁢ 101 Rh reaction cross section was reasonably well reproduced by a subset of photon strength functions and level densities, though the strength to the ground state of 101 Rh was underestimated at higher incident gamma energies. The 102 Pd ⁢(𝛾,𝛼)⁢ 98 Ru was in general overpredicted by the various alpha-nucleus optical model potentials. Conclusions: While the theoretical cross sections used to model the (𝛾,𝑝) reactions for the p process may be reasonable, a more careful approach is needed in the case of (𝛾,𝛼). Further work to probe gamma-induced reaction cross sections at and near the p nuclei is warranted.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

A Continuous Galactic Line Source of Axions: The Remarkable Case of 23 Na

Here, we argue that $^{23}$Na is a potentially significant source of galactic axions. For temperatures $\gtrsim 7 \times 10^8$K -- characteristic of carbon burning in the massive progenitors of supernovae and ONeMg white dwarfs -- the 440 keV first excited state of $^{23}$Na is thermally populated, with its repeated decays pumping stellar energy into escaping axions. Odd-A nuclear abundances are typically very low in high-temperature stellar environments (or absent entirely due to burn-up). $^{23}$Na is an exception: $\approx 0.1 M_\odot$ of the isotope is synthesized during carbon burning then maintained at $\approx 10^9$K for times ranging up to $6 \times 10^4$y. Using MESA simulations, a galactic model, and sampling over progenitor masses, locations, and evolutionary stages, we find a continuous flux at earth of $\langle ϕ_a \rangle \approx 22$/cm$^2$s for $g^\mathrm{eff}_{aNN} = 10^{-9}$. Some fraction of these axions convert to photons as they propagate through the galactic magnetic field, producing a distinctive 440 keV line $γ$ ray detectable by all-sky detectors like the Compton Spectrometer and Imager (COSI). Assuming a 1$μ$G galactic magnetic field and a sufficiently light axion mass, we find that COSI will be able to probe $| g_{aNN}^\mathrm{eff} g_{a γγ} | \gtrsim1.8 \times 10^{-22}$ GeV$^{-1}$ at $3σ$ after two years of surveying.

Dark matter↗