Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “NUCLEOSYNTHESIS”

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.

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

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Photon strength functions and nuclear level densities: invaluable input for nucleosynthesis

The pivotal role of nuclear physics in nucleosynthesis processes is being investigated, in particular the intricate influence of photon strength functions (PSFs) and nuclear level densities (NLDs) on shaping the outcomes of the i-, r- and p-processes. Exploring diverse NLD and PSF model combinations uncovers large uncertainties for (p, γ ), (n, γ ) and ( α , γ ) rates across many regions of the nuclear chart. These lead to potentially significant abundance variations of the nucleosynthesis processes and highlight the importance of accurate experimental nuclear data. Theoretical insights and advanced experimental techniques lay the ground work for profound understanding that can be gained of nucleosynthesis mechanisms and the origin of the elements. Recent results further underscore the effect of PSF and NLD data and its contribution to understanding abundance distributions and refining knowledge of the intricate nucleosynthesis processes. This article is part of the theme issue ‘The liminal position of Nuclear Physics: from hadrons to neutron stars’.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1994

Production of Lithium, Beryllium, and Boron from Baryon inhomogeneous primordial nucleosynthesis

We investigate the possibility that inhomogeneous nucleosynthesis may eventually be used to explain the abundances of Li-6, Be-9, and B in Population II stars. The present work differs from previous studies in that we have used a more extensive reaction network. It is demonstrated that in the simplest scenario the abundances of the light elements with A less than or = 7 constrain the separation of inhomogeneities to sufficently small scales that the model is indistinguishable from homogeneous nucleosynthesis and that the abundnace of Li-6, Be-9, and B are then below observations by several orders of magnitude. This conclusion does not depend on the Li-7 constraint. We also examine alternative scenarios which involve a post-nucleosynthesis reprocessing of the light elements to reproduce the observed abundances of Li and B, while allowing for a somewhat higher baryon density (still well below the cosmological critical density). Future B/H measurements may be able to exclude even this exotic scenario and further restrict primirdial nucleosynthesis to approach the homogeneous model conclusions.

Thomas, David↗
DOE OSTI2014

The Karlsruhe Astrophysical Database of Nucleosynthesis in Stars Project – Status and Prospects

The KADoNiS (Karlsruhe Astrophysical Database of Nucleosynthesis in Stars) project is an astrophysical online database for cross sections relevant for nucleosynthesis in the s process and the γ process. The s-process database ( (http://www.kadonis.org)) was started in 2005 and is presently facing its 4th update (KADoNiS v1.0). The γ-process database (KADoNiS-p, (http://www.kadonis.org/pprocess)) was recently revised and re-launched in March 2013. Both databases are compilations for experimental cross sections with relevance to heavy ion nucleosynthesis. For the s process recommended Maxwellian averaged cross sections for kT=5−100 keV are given for more than 360 isotopes between {sup 1}H and {sup 210}Bi. For the γ-process database all available experimental data from (p,γ),(p,n),(p,α),(α,γ),(α,n), and (α,p) reactions between {sup 70}Ge and {sup 209}Bi in or close to the respective Gamow window were collected and can be compared to theoretical predictions. The aim of both databases is a quick and user-friendly access to the available data in the astrophysically relevant energy regions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

The γ -process nucleosynthesis in core-collapse supernovae

The γ-process nucleosynthesis in core-collapse supernovae is generally accepted as a feasible process for the synthesis of neutron-deficient isotopes beyond iron. However, crucial discrepancies between theory and observations still exist: the average yields of γ-process nucleosynthesis from massive stars are still insufficient to reproduce the solar distribution in galactic chemical evolution calculations, and the yields of the Mo and Ru isotopes are a factor of ten lower than the yields of the other γ-process nuclei. We investigate the γ-process in five sets of core-collapse supernova models published in the literature with initial masses of 15, 20, and 25 M ⊙ at solar metallicity. We compared the γ-process overproduction factors from the different models. To highlight the possible effect of nuclear physics input, we also considered 23 ratios of two isotopes close to each other in mass relative to their solar values. Further, we investigated the contribution of C–O shell mergers in the supernova progenitors as an additional site of the γ-process. Our analysis shows that a large scatter among the different models exists for both the γ-process integrated yields and the isotopic ratios. We find only ten ratios that agree with their solar values, all the others differ by at least a factor of three from the solar values in all the considered sets of models. The γ-process within C–O shell mergers mostly influences the isotopic ratios that involve intermediate and heavy proton-rich isotopes with A > 100. We conclude that there are large discrepancies both among the different data sets and between the model predictions and the solar abundance distribution. More calculations are needed; particularly updating the nuclear network, because the majority of the models considered in this work do not use the latest reaction rates for the γ-process nucleosynthesis. Moreover, the role of C–O shell mergers requires further investigation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Nucleosynthesis in Magnetohydrodynamical Jets from Collapsars

We investigate the heavy-element nucleosynthesis of a massive star whose mass in the main sequence stage is M{sub ms} = 70 M{sub {center_dot}}. Detailed calculations of the nucleosynthesis are performed during the hydrostatic stellar evolution until the core composed of iron-group nuclei begins to collapse. As a supernova explosion model, a collapsar model is constructed whose jets are driven by magnetohydrodynamical effects of a differentially rotating core. The heavy-element nucleosynthesis inside the jet of a collapsar model is followed along the trajectories of stream lines of the jet. We combine the results of both hydrostatic and heavy-element nucleosyntheses to compare with the solar abundances. We find that neutron-rich elements of 70<A<140 are highly overproduced relative to the solar abundances. Therefore, we conclude that this scenario should be rare and elements of A < or approx. 70 are compensated for other supernova explosion models. We find also that different mass formula changes significantly the production of elements of A>140.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Nucleosynthesis in a massive star associated with magnetohydrodynamical jets from collapsars

We investigate the nucleosynthesis during the stellar evolution and the jet-like supernova explosion of a massive star of 70 M{sub Circled-Dot-Operator} having the solar metallicity in the main sequence stage. The nucleosynthesis calculations have been performed with large nuclear reaction networks, where the weak s-, p-, and r-processes are taken into account. As a result s-elements of 60 > A > 90 and r-elements of 90 > A > 160 are highly overproduced relative to the solar system abundances. We find that the Sr-Y-Zr isotopes are primarily synthesized in the explosive nucleosynthesis which could be one of the sites of the lighter element primary process (LEPP).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Primordial nucleosynthesis: A cosmological point of view

Primordial nucleosynthesis remains as one of the pillars of modern cosmology. It is the test-ing ground upon which all cosmological models must ultimately rest. It is our only probe of the universe during the first few minutes of cosmic expansion and in particular during the important radiation-dominated epoch. These lectures review the basic equations of space-time, cosmology, and big bang nucleosynthesis. We will then review the current state of observational constraints on primordial abundances along with the key nuclear reactions and their uncertainties. We summarize which nuclear measure-ments are most crucial during the big bang. We also review various cosmological models and their constraints. In particular, we summarize the constraints that big bang nucleosynthesis places upon the possible time variation of fundamental constants, along with constraints on the nature and origin of dark matter and dark energy, long-lived supersymmetric particles, gravity waves, and the primordial magnetic field.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Neutrinos and nucleosynthesis in core-collapse supernovae

Massive stars (M > 8-10 M{sub ⊙}) undergo core collapse at the end of their life and explode as supernova with ~ 10⁵¹ erg of kinetic energy. While the detailed supernova explosion mechanism is still under investigation, reliable nucleosynthesis calculations based on successful explosions are needed to explain the observed abundances in metal-poor stars and to predict supernova yields for galactic chemical evolution studies. To predict nucleosynthesis yields for a large number of progenitor stars, computationally efficient explosion models are required. We model the core collapse, bounce and subsequent explosion of massive stars assuming spherical symmetry and using detailed microphysics and neutrino physics combined with a novel method to artificially trigger the explosion (PUSH). We discuss the role of neutrinos, the conditions in the ejecta, and the resulting nucleosynthesis.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

NUCLEOSYNTHESIS IN CORE-COLLAPSE SUPERNOVA EXPLOSIONS TRIGGERED BY A QUARK-HADRON PHASE TRANSITION

We explore heavy-element nucleosynthesis in the explosion of massive stars that are triggered by a quark-hadron phase transition during the early post-bounce phase of core-collapse supernovae. The present study is based on general-relativistic radiation hydrodynamics simulations with three-flavor Boltzmann neutrino transport in spherical symmetry, which utilize a quark-hadron hybrid equation of state based on the MIT bag model for strange quark matter. The quark-hadron phase transition inside the stellar core forms a shock wave propagating toward the surface of the proto-neutron star. This shock wave results in an explosion and ejects neutron-rich matter from the outer accreted layers of the proto-neutron star. Later, during the cooling phase, the proto-neutron star develops a proton-rich neutrino-driven wind. We present a detailed analysis of the nucleosynthesis outcome in both neutron-rich and proton-rich ejecta and compare our integrated nucleosynthesis with observations of the solar system and metal-poor stars. For our standard scenario, we find that a 'weak' r-process occurs and elements up to the second peak (A {approx} 130) are successfully synthesized. Furthermore, uncertainties in the explosion dynamics could barely allow us to obtain the strong r-process which produces heavier isotopes, including the third peak (A {approx} 195) and actinide elements.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

NUCLEOSYNTHESIS IN THE OUTFLOWS ASSOCIATED WITH ACCRETION DISKS OF TYPE II COLLAPSARS

We investigate nucleosynthesis inside the outflows from gamma-ray burst (GRB) accretion disks formed by the Type II collapsars. In these collapsars, massive stars undergo core collapse to form a proto-neutron star initially, and a mild supernova (SN) explosion is driven. The SN ejecta lack momentum, and subsequently this newly formed neutron star gets transformed to a stellar mass black hole via massive fallback. The hydrodynamics and the nucleosynthesis in these accretion disks have been studied extensively in the past. Several heavy elements are synthesized in the disk, and much of these heavy elements are ejected from the disk via winds and outflows. We study nucleosynthesis in the outflows launched from these disks by using an adiabatic, spherically expanding outflow model, to understand which of these elements thus synthesized in the disk survive in the outflow. While studying this, we find that many new elements like isotopes of titanium, copper, zinc, etc., are present in the outflows. {sup 56}Ni is abundantly synthesized in most of the cases in the outflow, which implies that the outflows from these disks in a majority of cases will lead to an observable SN explosion. It is mainly present when outflow is considered from the He-rich, {sup 56}Ni/{sup 54}Fe-rich zones of the disks. However, outflow from the Si-rich zone of the disk remains rich in silicon. Although emission lines of many of these heavy elements have been observed in the X-ray afterglows of several GRBs by Chandra, BeppoSAX, XMM-Newton, etc., Swift seems to have not yet detected these lines.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Big bang nucleosynthesis revisited via Trojan Horse method measurements

Nuclear reaction rates are among the most important input for understanding primordial nucleosynthesis and, therefore, for a quantitative description of the early universe. An up-to-date compilation of direct cross-sections of {sup 2}H(d, p){sup 3}H, {sup 2}H(d, n){sup 3}He, {sup 7}Li(p, α){sup 4}He, and {sup 3}He(d, p){sup 4}He reactions is given. These are among the most uncertain cross-sections used and input for big bang nucleosynthesis calculations. Their measurements through the Trojan Horse method are also reviewed and compared with direct data. The reaction rates and the corresponding recommended errors in this work were used as input for primordial nucleosynthesis calculations to evaluate their impact on the {sup 2}H, {sup 3,4}He, and {sup 7}Li primordial abundances, which are then compared with observations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

EVOLUTION, NUCLEOSYNTHESIS, AND YIELDS OF LOW-MASS ASYMPTOTIC GIANT BRANCH STARS AT DIFFERENT METALLICITIES. II. THE FRUITY DATABASE

By using updated stellar low-mass stars models, we systematically investigate the nucleosynthesis processes occurring in asymptotic giant branch (AGB) stars. In this paper, we present a database dedicated to the nucleosynthesis of AGB stars: FRANEC Repository of Updated Isotopic Tables and Yields (FRUITY). An interactive Web-based interface allows users to freely download the full (from H to Bi) isotopic composition, as it changes after each third dredge-up (TDU) episode and the stellar yields the models produce. A first set of AGB models, having masses in the range 1.5 {<=}M/M{sub Sun} {<=} 3.0 and metallicities 1 Multiplication-Sign 10{sup -3} {<=} Z {<=} 2 Multiplication-Sign 10{sup -2}, is discussed. For each model, a detailed description of the physical and the chemical evolution is provided. In particular, we illustrate the details of the s-process and we evaluate the theoretical uncertainties due to the parameterization adopted to model convection and mass loss. The resulting nucleosynthesis scenario is checked by comparing the theoretical [hs/ls] and [Pb/hs] ratios to those obtained from the available abundance analysis of s-enhanced stars. On the average, the variation with the metallicity of these spectroscopic indexes is well reproduced by theoretical models, although the predicted spread at a given metallicity is substantially smaller than the observed one. Possible explanations for such a difference are briefly discussed. An independent check of the TDU efficiency is provided by the C-stars luminosity function. Consequently, theoretical C-stars luminosity functions for the Galactic disk and the Magellanic Clouds have been derived. We generally find good agreement with observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Statistical methods for thermonuclear reaction rates and nucleosynthesis simulations

Rigorous statistical methods for estimating thermonuclear reaction rates and nucleosynthesis are becoming increasingly established in nuclear astrophysics. The main challenge being faced is that experimental reaction rates are highly complex quantities derived from a multitude of different measured nuclear parameters (e.g., astrophysical S-factors, resonance energies and strengths, particle and γ-ray partial widths). We discuss the application of the Monte Carlo method to two distinct, but related, questions. First, given a set of measured nuclear parameters, how can one best estimate the resulting ther- monuclear reaction rates and associated uncertainties? Second, given a set of appropriate reaction rates, how can one best estimate the abundances from nucleosynthesis (i.e., reaction network) calculations? The techniques described here provide probability density functions that can be used to derive statisti- cally meaningful reaction rates and final abundances for any desired coverage probability. Examples are given for applications to s-process neutron sources, core-collapse supernovae, classical novae, and Big Bang nucleosynthesis.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

r-PROCESS NUCLEOSYNTHESIS IN DYNAMICALLY EJECTED MATTER OF NEUTRON STAR MERGERS

Although the rapid neutron-capture process, or r-process, is fundamentally important for explaining the origin of approximately half of the stable nuclei with A > 60, the astrophysical site of this process has not been identified yet. Here we study r-process nucleosynthesis in material that is dynamically ejected by tidal and pressure forces during the merging of binary neutron stars (NSs) and within milliseconds afterward. For the first time we make use of relativistic hydrodynamical simulations of such events, defining consistently the conditions that determine the nucleosynthesis, i.e., neutron enrichment, entropy, early density evolution and thus expansion timescale, and ejecta mass. We find that 10{sup -3}-10{sup -2} M{sub sun} are ejected, which is enough for mergers to be the main source of heavy (A {approx}> 140) galactic r-nuclei for merger rates of some 10{sup -5} yr{sup -1}. While asymmetric mergers eject 2-3 times more mass than symmetric ones, the exact amount depends weakly on whether the NSs have radii of {approx}15 km for a 'stiff' nuclear equation of state (EOS) or {approx}12 km for a 'soft' EOS. r-process nucleosynthesis during the decompression becomes largely insensitive to the detailed conditions because of efficient fission recycling, producing a composition that closely follows the solar r-abundance distribution for nuclei with mass numbers A > 140. Estimating the light curve powered by the radioactive decay heating of r-process nuclei with an approximative model, we expect high emission in the B-V-R bands for 1-2 days with potentially observable longer duration in the case of asymmetric mergers because of the larger ejecta mass.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Systematic exploration of heavy element nucleosynthesis in protomagnetar outflows

ABSTRACT We study the nucleosynthesis products in neutrino-driven winds from rapidly rotating, highly magnetized and misaligned protomagnetars using the nuclear reaction network SkyNet. We adopt a semi-analytic parametrized model for the protomagnetar and systematically study the capabilities of its neutrino-driven wind for synthesizing nuclei and eventually producing ultra-high energy cosmic rays (UHECRs). We find that for neutron-rich outflows (Ye < 0.5), synthesis of heavy elements ($\overline{A}\sim 20-65$) is possible during the first $\sim 10\, {\rm s}$ of the outflow, but these nuclei are subjected to composition-altering photodisintegration during the epoch of particle acceleration at the dissipation radii. However, after the first $\sim 10\, {\rm s}$ of the outflow, nucleosynthesis reaches lighter elements ($\overline{A}\sim 10-50$) that are not subjected to subsequent photodisintegration. For proton-rich (Ye ≥ 0.5) outflows, synthesis is more limited ($\overline{A}\sim 4-15$). These suggest that while protomagnetars typically do not synthesize nuclei heavier than second r-process peak elements, they are intriguing sources of intermediate/heavy mass UHECRs. For all configurations, the most rapidly rotating protomagnetars are more conducive for nucleosynthesis with a weaker dependence on the magnetic field strength.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Fast, differentiable, and extensible big bang nucleosynthesis package

Here, we introduce light isotope nucleosynthesis with JAX (LINX), a new differentiable public big bang nucleosynthesis code designed for fast parameter estimation. By leveraging JAX, LINX achieves both speed and differentiability, enabling the use of Bayesian inference, including gradient-based methods. We discuss the formalism used in LINX for rapid primordial elemental abundance predictions and give examples of how LINX can be used. When combined with differentiable cosmic microwave background power spectrum emulators, LINX can be used for joint cosmic microwave background and big bang nucleosynthesis analyses without requiring extensive computational resources, including on personal hardware.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Collaborative Research: Neutrinos & Nucleosynthesis in Hot Dense Matter

It is now firmly established that neutrinos, which are copiously produced in the hot and dense core of the supernova, play a role in the supernova explosion mechanism and in the synthesis of heavy elements through a phenomena known as r-process nucleosynthesis. They are also detectable in terrestrial neutrino experiments, and serve as a probe of the extreme environment and complex dynamics encountered in the supernova. The major goal of the UW research activity relevant to this project was to calculate the neutrino interaction rates in hot and dense matter of relevance to core collapse supernova. These serve as key input physics in large scale computer simulations of the supernova dynamics and nucleosynthesis being pursued at national laboratories here in the United States and by other groups in Europe and Japan. Our calculations show that neutrino production and scattering rate are altered by the nuclear interactions and that these modifications have important implications for nucleosynthesis and terrestrial neutrino detection. The calculation of neutrino rates in dense matter are difficult because nucleons in the dense matter are strongly coupled. A neutrino interacts with several nucleons and the quantum interference between scattering off different nucleons depends on the nature of correlations between them in dense matter. To describe these correlations we used analytic methods based on mean field theory and hydrodynamics, and computational methods such as Quantum Monte Carlo. We found that due to nuclear effects neutrino production rates at relevant temperatures are enhanced, and that electron neutrinos are more easily absorbed than anti-electron neutrinos in dense matter. The latter, was shown to favor synthesis of heavy neutron-rich elements in the supernova.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

The Origin of Chemical Elements: Connecting Laboratory Nuclear Astrophysics with Astronomical Observations through Nucleosynthesis Modeling

Nuclear astrophysics is a field at the frontier of nuclear science which continues to enjoy significant progress and exciting prospects for the future. It addresses the fundamental question of where and how the chemical elements are made. Except for hydrogen and helium, all other chemical elements are made either in stars or in cosmic explosions such as supernovae or neutron star mergers. To understand the formation of elements we need to understand the relevant nuclear physics processes that govern the interaction between nuclei. We need to understand the conditions in the star or the explosion under which these nuclear processes take place. And we need to understand how individual events of element formation contribute to the overall chemical enrichment of our Galaxy over time. Experimental facilities allow for terrestrial experiments on the nuclear physics governing the element synthesis. Earth-based and space-based telescopes probe the Galaxy around us and provide information about the conditions in stars and supernovae, and about the chemical element enrichment of these different environments. Numerical simulations of stars, supernovae, and other astrophysical phenomena allow us to probe the conditions of extreme densities and temperatures required for element synthesis. Nucleosynthesis research is ideally posed to integrate advances from all three of these areas and advance our understanding of how and where elements are made. Nucleosynthesis research provides theory support for experiments and observations. And it makes predictions that can be tested in nuclear physics experiments and astronomical observations. The goals of this award were in three main areas: 1. Develop and implement an effective core-collapse supernova model that is computationally efficient and that captures the relevant physics for the scientific questions of interest 2. Advance our understanding of the synthesis of the lightest heavy elements 3. Increase the realism of supernova nucleosynthesis and determine its dependence on the properties of the exploding star As the projects progressed, an additional focus was added to this list: 1. Study the explosion properties and the signals from the most massive stars.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗