SEARCH · Search NASA

Results for “r process”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4

All sources NASA NTRS DOE OSTI

NASA NTRS1982

The heavy element yields of neutron capture nucleosynthesis

Consideration of the contribution made to the abundances of the heavy element isotopes by the S- and R-processes of nucleosynthesis has led to the determination that the previous assumption concerning the exclusive alignment of isobars to one or the other of these processes is probably in error. If the relatively small odd and even mass number abundance fluctuations characterizing R-process abundances are always the case, as assumed by this study, S-process contributions to the abundances of R-process isobars are substantial, consistent with transient flashing episodes in the S-process neutron production processes. A smooth and monotonically-decreasing curve of the abundance of the S-process yields times the neutron capture cross-section versus mass number is therefore the primary tool for the separation of the abundances due to the two processes.

Cameron, A. G. W.↗

NASA NTRS1990

The interpretation of solar system abundances at the N = 50 neutron shell

New data on CI chondrite abundances demonstrate a high degree of smoothness for the A = 75 - 100 mass range for odd A nuclei, except a single element peak at K ascribable to the s-process peak for the N = 50 neutron shell. Literature estimates of s-process abundances, Ns, permit a smooth Ns curve to be drawn; however the resultant 'non-s' abundance curve (nominally r-process) does not show a peak analogous to peaks associated with the N = 82 or 126 shells. Assuming the systematics of the r-process even and odd A abundance peaks at the N = 82 and 126 shells apply to N = 50, the odd A r-process peak for N = 50 can be obtained, which in turn permits a new calculation of Ns for odd A.

Burnett, D. S.↗

NASA NTRS1988

Cosmological quantum chromodynamics, neutron diffusion, and the production of primordial heavy elements

A simple one-dimensional model is used to describe the evolution of neutron density before and during nucleosynthesis in a high-entropy bubble left over from the cosmic quark-hadron phase transition. It is shown why cosmic nucleosynthesis in such a neutron-rich environment produces a surfeit of elements heavier than lithium. Analytical and numerical techniques are used to estimate the abundances of carbon, nitrogen, and heavier elements up to Ne-22. A high-density neutron-rich region produces enough primordial N-14 to be observed in stellar atmospheres. It shown that very heavy elements may be created in a cosmological r-process; the neutron exposure in the neutron-rich regions is large enough for the Ne-22 to trigger a catastrophic r-process runaway in which the quantity of heavy elements doubles in much less than an expansion time due to fission cycling. A primordial abundance of r-process elements is predicted to appear as an excess of rare earth elements in extremely metal-poor stars.

Applegate, J. H.↗

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 OSTI2025

Long-lived neutron-star remnants from asymmetric binary neutron star mergers: element formation, kilonova signals and gravitational waves

We present 3D general-relativistic neutrino-radiation hydrodynamics simulations of two asymmetric binary neutron star mergers producing long-lived neutron stars remnants and spanning a fraction of their cooling time scale. The mergers are characterized by significant tidal disruption with neutron rich material forming a massive disc around the remnant. The latter develops one-armed dynamics that is imprinted in the emitted kilo-Hertz gravitational waves. Angular momentum transport to the disc is initially driven by spiral-density waves and enhanced by turbulent viscosity and neutrino heating on longer timescales. The mass outflows are composed by neutron-rich dynamical ejecta of mass ∼10 −3 –10 −2 M ⊙ followed by a persistent spiral-wave/neutrino-driven wind of ≳ 10 −2 M ⊙ with material spanning a wide range of electron fractions, ∼0.1–0.55. Dynamical ejecta (winds) have fast velocity tails up to ∼0.8 (∼0.4) c. The outflows are further evolved to days timescale using 2D ray-by-ray radiation-hydrodynamics simulations that include an online nuclear network. We find complete r-process yields and identify the production of 56 Ni and the subsequent decay chain to 56 Co and 56 Fe. Synthetic kilonova light curves predict an extended (near-) infrared peak a few days postmerger originating from r-process in the neutron-rich/high-opacity ejecta and UV/optical peaks at a few hours (ten minutes) postmerger originating from weak r-process (free-neutron decay) in the faster ejecta components. Additionally, the fast tail of tidal origin generates kilonova afterglows potentially detectable in radio and X band on a few to ten years time scale. Quantitative effects originating from the tidal disruption merger dynamics are reflected in the multimessenger emissions.

abundances↗

DOE OSTI2024

Element Formation in Radiation-hydrodynamics Simulations of Kilonovae

Abstract Understanding the details of r -process nucleosynthesis in binary neutron star merger (BNSM) ejecta is key to interpreting kilonova observations and identifying the role of BNSMs in the origin of heavy elements. We present a self-consistent, two-dimensional, ray-by-ray radiation-hydrodynamic evolution of BNSM ejecta with an online nuclear network (NN) up to a timescale of days. For the first time, an initial numerical relativity ejecta profile composed of the dynamical component and spiral-wave and disk winds is evolved including detailed r -process reactions and nuclear heating effects. A simple model for the jet energy deposition is also included. Our simulation highlights that the common approach of relating in postprocessing the final nucleosynthesis yields to the initial thermodynamic profile of the ejecta can lead to inaccurate predictions. Moreover, we find that neglecting the details of the radiation-hydrodynamic evolution of the ejecta in nuclear calculations can introduce deviations of up to 1 order of magnitude in the final abundances of several elements, including very light and second r -process peak elements. The presence of a jet affects element production only in the innermost part of the polar ejecta, and it does not alter the global nucleosynthesis results. Overall, our analysis shows that employing an online NN improves the reliability of nucleosynthesis and kilonova light-curve predictions.

Magistrelli, Fabio (ORCID:0009000509767851)↗

NASA NTRS2009

The Orbiting Astrophysical Spectrometer In Space (OASIS)

The Orbiting Astrophysical Spectrometer In Space (OASIS) is an Advanced Concept currently understudy at NASA as a mission for the next decade. The goal of the OASIS mission is to identify a local site or sites where galactic cosmic rays (GCR) originate and are accelerated. The mission will allow GCR data to be used to investigate how elements are made and distributed in the galaxy and to improve our understanding of supernovae and the nucleosynthesis of the heavy elements needed for life. OASIS consists of two instruments that provide complementary data on the location and nature of the source(s) through investigating the composition of ultraheavy nuclei and the energy spectrum of electrons. OASIS will measure the relative abundances in the actinide group to determine the age of the r-process material in GCRs. The presence of young r-process material would indicate that GCRs are a sample of the interstellar medium in OB associations. OASIS will follow the electron spectrum to its high-energy end. The energy where this spectrum ends will tell us the distance to the nearest GCR source(s). OASIS will look for spectral features and anisotropy in the high energy electron spectrum that are expected to appear when only a few of the nearest sources can contribute the electron flux. Possibly these measurements will lead to the identification of the nearest cosmic ray electron source.

Christl, Mark J.↗

DOE OSTI2024

Robustness of neutron star merger simulations to changes in neutrino transport and neutrino-matter interactions

Binary neutron star mergers play an important role in nuclear astrophysics: Their gravitational wave and electromagnetic signals carry information about the equation of state of cold matter above nuclear saturation density, and they may be one of the main sources of r-process elements in the Universe. Neutrino-matter interactions during and after merger impact the properties of these electromagnetic signals and the relative abundances of the produced r-process elements. Existing merger simulations are, however, limited in their ability to realistically model neutrino transport and neutrino-matter interactions. Here, we perform a comparison of the impact of the use of state-of-the art two-moment or Monte Carlo transport schemes on the outcome of merger simulations, for a single binary neutron star system with a short-lived neutron star remnant [(5–10) ms]. We also investigate the use of different reaction rates in the simulations. While the best transport schemes generally agree well on the qualitative impact of neutrinos on the system, differences in the behavior of the high-density regions can significantly impact the collapse time and the properties of the hot tidal arms in this metastable merger remnant. The chosen interaction rates and transport algorithm as well as recent improvements by Radice et al. to the two-moment algorithms can all contribute to changes at the (10–30)% level in the global properties of the merger remnant and outflows. Furthermore, the limitations of previous moment schemes fixed by Radice et al. also appear sufficient to explain the large difference that we observed in the production of heavy-lepton neutrinos in a previous comparison of Monte Carlo and moment schemes in the context of a low-mass binary neutron star system.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2024

Do we owe our existence to gravitational waves?

Two heavy elements essential to human biology are thought to have been produced by the astrophysical r-process, which occurs in neutron-rich environments: iodine is a constituent of thyroid hormones that affect many physiological processes including growth and development, body temperature and heart rate, and bromine is essential for tissue development and architecture. Collisions of neutron stars (kilonovae) have been identified as sources of r-process elements including tellurium, which is adjacent to iodine in the periodic table, and lanthanides. Neutron-star collisions arise from energy loss due to gravitational-wave emission from binary systems, leading us to suggest that gravitational waves have played a key role in enabling human life by producing iodine and bromine. We propose probing this proposal by searching in lunar material for live 129 I deposited by a recent nearby kilonova explosion.

Human biochemistry↗

DOE OSTI2026

Kilonovae and Long-duration Gamma-Ray Bursts

Recent detections of kilonova-like emission following long-duration gamma-ray bursts GRB 211211A and GRB 230307A have been interpreted as originating from the merger of two neutron stars. In this work, we demonstrate that these observations are also consistent with nucleosynthesis originating from a collapsar scenario. Our model is capable of reproducing the observed optical and infrared light curves using a single, weak r-process component. The absence of lanthanide-rich material in our model, consistent with the data, challenges the prevailing interpretation that a red evolution in such transients necessarily indicates the presence of heavy r-process elements.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2024

Actinide signatures in low electron fraction kilonova ejecta

ABSTRACT Neutron star (NS) mergers are known to produce heavy elements through rapid neutron capture (r-process) nucleosynthesis. Actinides are expected to be created solely by the r-process in the most neutron-rich environments. Confirming if NS mergers provide the requisite conditions for actinide creation is therefore central to determining their origin in the Universe. Actinide signatures in kilonova (KN) spectra may yield an answer, provided adequate models are available in order to interpret observational data. In this study, we investigate actinide signatures in neutron-rich merger ejecta. We use three ejecta models with different compositions and radioactive power, generated by nucleosynthesis calculations using the same initial electron fraction ($Y_e = 0.15$) but with different nuclear physics inputs and thermodynamic expansion history. These are evolved from 10 to 100 d after merger using the sumo non-local thermodynamic equilibrium (NLTE) radiative transfer code. We highlight how uncertainties in nuclear properties, as well as choices in thermodynamic trajectory, may yield entirely different outputs for equal values of $Y_e$. We consider an actinide-free model and two actinide-rich models, and find that the emergent spectra and light-curve evolution are significantly different depending on the amount of actinides present, and the overall decay properties of the models. We also present potential key actinide spectral signatures, of which doubly ionized $_{89}$Ac and $_{90}$Th may be particularly interesting as spectral indicators of actinide presence in KN ejecta.

Pognan, Quentin (ORCID:0000000152550782)↗

DOE OSTI2024

Collective Neutrino Oscillations and Heavy-element Nucleosynthesis in Supernovae: Exploring Potential Effects of Many-body Neutrino Correlations

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

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1973

Are large time differences in meteorite formation real

Considerations are given concerning the interpretation of the results of two types of cosmochronological dating in order to examine the validity of the conclusions inferred from these results that the time intervals between the formation of various meteorite samples are very great. It is theorized that the isotopic differences between Angra dos Reis and other basaltic achondrites may be due to real fluctuations between the relative abundances of s-process and r-process nucleosynthesis products at a level delta about 0.001.

Cameron, A. G. W.↗

NASA NTRS1976

Transition from incoherence to coherence in the spontaneous emission of extended systems

Using the results of a previous paper, we study the evolution of a completely excited system of N two-level atoms, distributed in a circular cylinder with dimensions much larger than the wavelength, interacting with all modes of radiation field. We emphasize the distinction between r-conserving (rC) and r-nonconserving (rNC) processes (r is the so-called cooperation number). Considering the number of photons emitted as the discrete independent variable, the evolution is described by a partial difference equation. Numerical solutions of this equation show the transition from rNC dominance at the beginning to rC dominance later. This is also a transition from incoherent to coherent emission of radiation.

Lee, C. T.↗

NASA NTRS1988

Evolution of heavy-element abundances in the Galactic halo and disk

The constraints on the universal energy density and cosmological constant from cosmochronological ages and the Hubble age are reviewed. Observational evidence for the galactic chemical evolution of the heavy-element chronometers is descirbed in the context of numerical models. The viability of the recently discovered Th/Nd stellar chronometer is discussed, along with the suggestion that high r-process abundances in metal-poor stars may have resulted from a primordial r-process, as may be required by some inhomogeneous cosmologies.

Mathews, G. J.↗

DOE OSTI2025

Comparison of the earliest NC and CC planetesimals: Evidence from ungrouped iron meteorites

Isotope anomalies in meteorites reveal a fundamental dichotomy between Non-Carbonaceous- (NC) and Carbonaceous-type (CC) planetary bodies. Until now, this dichotomy is established for the major meteorite groups, representing about 36 distinct parent bodies. Ungrouped meteorites represent an even larger number of additional parent bodies, but whether they conform to the overall NC-CC dichotomy is unknown. Here, the genetics and chronology of 26 ungrouped iron meteorites are considered through nucleosynthetic Mo and radiogenic W isotopic compositions. Secondary cosmic ray-induced modifications of these isotope compositions are corrected using Pt isotope measurements on the same samples. We find that all of the ungrouped irons have Mo isotope anomalies within the range of the major meteorite groups and confirm the NC-CC dichotomy for Mo, where NC and CC meteorites define two distinct, subparallel s-process mixing lines. All ungrouped NC irons fall on the NC-line, which is now precisely defined for 41 distinct parent bodies. The ungrouped CC irons show scatter around the CC-line indicative of small r-process Mo heterogeneities among these samples. These r-process Mo isotope variations correlate with O isotope anomalies, most likely reflecting mixing of CI chondrite-like matrix, chondrule precursors, and Ca-Al-rich inclusions. This implies that CC iron meteorite parent bodies accreted the same nebular components as the later-formed carbonaceous chondrites. The Hf-W model ages of core formation for the ungrouped irons overlap with those of the iron meteorite groups from each reservoir and reveal a narrow age peak at ∼3.3 Ma after Ca-Al-rich inclusions for the CC irons. By contrast, the NC irons display more variable ages, including younger ages indicative of impact-induced melting events, which seem absent among the CC irons. This is attributed to the more fragile and porous nature of the CC bodies, making impact-induced melting on their surfaces difficult. The chemical characteristics of all iron meteorites together reveal slightly more oxidizing conditions during core formation for CC compared to NC irons. More strikingly, strong depletions in moderately volatile elements, typical of many iron meteorite parent bodies, predominantly occur among CC irons, for reasons that remain unclear at present.

Chondrite components↗

NASA NTRS1982

The abundance of the actinides in the cosmic radiation as measured on HEAO 3

The HEAO 3 detector of heavy cosmic-ray nuclei has observed one possible actinide nucleus and some 100 nuclei of the platinum-lead group of elements. The resulting upper limit of 3% for the abundance ratio of actinides to platinum-lead nuclides is significantly lower than previous results from other observations. This new limit is inconsistent with freshly synthesized, pure r-process sources for cosmic-ray nuclei in this charge interval but is consistent with a source having a composition similar to the solar system, or to aged r-process material. We observe no events with a charge greater than 96.

Binns, W. R.↗

NASA NTRS1981

Nucleosynthesis of neutron-rich heavy nuclei during explosive helium burning in massive stars

The production of heavy nuclei during explosive helium burning has been calculated using a hydrodynamical model of a 15-solar mass (Type II) supernova and an n-process nuclear reaction network. It is found that the resulting neutron-rich heavy nuclei are not produced in the relative abundances of solar-system r-process material, especially in the vicinity of Pt, nor are any actinides produced. These deficiencies reflect an inadequate supply of neutrons. However, some neutron-rich isotopes, normally associated with the r-process, are produced which may be significant for the production of isotopic anomalies in meteorites.

Blake, J. B.↗