The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
F. Gunsing - One of the best experts on this subject based on the ideXlab platform.
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measurement of 73ge n γ cross sections and implications for Stellar Nucleosynthesis
Physics Letters B, 2019Co-Authors: F. Gunsing, C Guerrero, C Ledererwoods, U Battino, Pedro G Ferreira, A Gawlik, S Heinitz, J LerendeguimarcoAbstract:Abstract 73Ge( n , γ ) cross sections were measured at the neutron time-of-flight facility n_TOF at CERN up to neutron energies of 300 keV, providing for the first time experimental data above 8 keV. Results indicate that the Stellar cross section at k T = 30 keV is 1.5 to 1.7 times higher than most theoretical predictions. The new cross sections result in a substantial decrease of 73Ge produced in stars, which would explain the low isotopic abundance of 73Ge in the solar system.
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Measurement of $^{73}$Ge($n,γ$) cross sections and implications for Stellar Nucleosynthesis
Phys.Lett.B, 2019Co-Authors: Claudia Lederer-woods, F. Gunsing, C Guerrero, U Battino, A Gawlik, S Heinitz, P. Ferreira, J. Lerendegui-marco, A. Mengoni, R ReifarthAbstract:73 Ge( n,γ ) cross sections were measured at the neutron time-of-flight facility n_TOF at CERN up to neutron energies of 300 keV, providing for the first time experimental data above 8 keV. Results indicate that the Stellar cross section at kT=30 keV is 1.5 to 1.7 times higher than most theoretical predictions. The new cross sections result in a substantial decrease of 73 Ge produced in stars, which would explain the low isotopic abundance of 73 Ge in the solar system.
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Resonances in neutron-induced reactions
Eur.Phys.J.Plus, 2018Co-Authors: F. GunsingAbstract:Resonances in neutron-induced reactions are important for reaction cross sections and nuclear data in general. They play a major role in nuclear technology for energy or medicine, but also in the study of nuclear level densities and Stellar Nucleosynthesis. An outline of the field of neutron physics is given, with a focus on neutron resonances, an introduction to the R-matrix formalism and the statistical behaviour of resonance observables.
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nuclear data for the thorium fuel cycle and the transmutation of nuclear waste
tew, 2016Co-Authors: F. Gunsing, F. Belloni, J. Andrzejewski, L. Audouin, M. Barbagallo, F. Bečvář, E. Berthoumieux, S Altstadt, V Becares, J. BillowesAbstract:Neutron-induced reaction cross sections play an important role in a wide variety of research fields, ranging from Stellar Nucleosynthesis, the investigation of nuclear level density studies, to applications of nuclear technology, including the transmutation of nuclear waste, accelerator-driven systems, and nuclear fuel cycle investigations. Simulations of nuclear technology applications largely rely on evaluated nuclear data libraries. These libraries are based both on experimental data and theoretical models. An outline of experimental nuclear data activities at CERN’s neutron time-of-flight facility, n_TOF, will be presented.
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Observation of Large Orbital Scissors Strength in Actinides
Acta Physica Polonica B, 2013Co-Authors: M. Guttormsen, F. Gunsing, L.a. Bernstein, A. Bürger, A. Görgen, T. W. Hagen, A.c. Larsen, T. Renstrøm, S. Siem, M. WiedekingAbstract:The M1-scissors resonance (SR) has been measured for the first time in the quasi-continuum of actinides. Particle-\gamma coincidences are recorded with deuteron and 3He induced reactions on 232Th. An unexpectedly strong integrated strength of BM1 = 11-15 \mu n2 is measured in the E\gamma = 1.0-3.5 MeV region. The increased \gamma-decay probability due to the scissors mode is important for cross-section calculations for future fuel cycles of fast nuclear reactors and may also have impact on Stellar Nucleosynthesis.
O. Straniero - One of the best experts on this subject based on the ideXlab platform.
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Nitrogen isotopes in AGB carbon stars and presolar SiC grains: a challenge for Stellar Nucleosynthesis
The Astrophysical journal letters, 2013Co-Authors: R. Hedrosa, C. Abia, S. Cristallo, M. Busso, I. Domínguez, S. Palmerini, Bertrand Plez, O. StranieroAbstract:Isotopic ratios of C, N, Si, and trace heavy elements in presolar SiC grains from meteorites provide crucial constraints to Nucleosynthesis. A long-debated issue is the origin of the so-called A+B grains, as for them no Stellar progenitor has so far been clearly identified on observational grounds. We report the first spectroscopic measurements of 14N/15N ratios in Galactic carbon stars of different spectral types and show that J- and some SC-type stars might produce A+B grains, even for 15N enrichments previously attributed to novae. We also show that most mainstream (MS) grains are compatible with the composition of N-type stars, but might also descend, in some cases, from SC stars. From the theoretical point of view, no astrophysical scenario can explain the C and N isotopic ratios of SC, J and N-type carbon stars together, as well as those of many grains produced by them. This poses urgent questions to Stellar physics.
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nitrogen isotopes in asymptotic giant branch carbon stars and presolar sic grains a challenge for Stellar Nucleosynthesis
The Astrophysical Journal, 2013Co-Authors: R. Hedrosa, C. Abia, S. Cristallo, M. Busso, I. Domínguez, S. Palmerini, Bertrand Plez, O. StranieroAbstract:Isotopic ratios of C, N, Si, and trace heavy elements in presolar SiC grains from meteorites provide crucial constraints to Nucleosynthesis. A long-debated issue is the origin of the so-called A+B grains, as of yet no Stellar progenitor thus far has been clearly identified on observational grounds. We report the first spectroscopic measurements of 14N/15N ratios in Galactic carbon stars of different spectral types and show that J- and some SC-type stars might produce A+B grains, even for 15N enrichments previously attributed to novae. We also show that most mainstream grains are compatible with the composition of N-type stars, but in some cases might also descend from SC stars. From a theoretical point of view, no astrophysical scenario can explain the C and N isotopic ratios of SC-, J-, and N-type carbon stars together, as well as those of many grains produced by them. This poses urgent questions to Stellar physics.
Stéphane Goriely - One of the best experts on this subject based on the ideXlab platform.
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pygmy and core polarization dipole modes in 206pb connecting nuclear structure to Stellar Nucleosynthesis
Physics Letters B, 2017Co-Authors: Stéphane Goriely, A P Tonchev, N Tsoneva, C Bhatia, C W Arnold, S L HammondAbstract:Abstract A high-resolution study of the electromagnetic response of 206Pb below the neutron separation energy is performed using a ( γ → , γ ′ ) experiment at the HI γ → S facility. Nuclear resonance fluorescence with 100% linearly polarized photon beams is used to measure spins, parities, branching ratios, and decay widths of excited states in 206Pb from 4.9 to 8.1 MeV. The extracted Σ B ( E 1 ) ↑ and Σ B ( M 1 ) ↑ values for the total electric and magnetic dipole strength below the neutron separation energy are 0.9 ± 0.2 e 2 fm 2 and 8.3 ± 2.0 μ N 2 , respectively. These measurements are found to be in very good agreement with the predictions from an energy-density functional (EDF) plus quasiparticle phonon model (QPM). Such a detailed theoretical analysis allows to separate the pygmy dipole resonance from both the tail of the giant dipole resonance and multi-phonon excitations. Combined with earlier photonuclear experiments above the neutron separation energy, one extracts a value for the electric dipole polarizability of 206Pb of α D = 122 ± 10 mb / MeV . When compared to predictions from both the EDF+QPM and accurately calibrated relativistic EDFs, one deduces a range for the neutron-skin thickness of R skin 206 = 0.12 – 0.19 fm and a corresponding range for the slope of the symmetry energy of L = 48 – 60 MeV . This newly obtained information is also used to estimate the Maxwellian-averaged radiative cross section Pb 205 ( n , γ ) Pb 206 at 30 keV to be σ = 130 ± 25 mb . The astrophysical impact of this measurement—on both the s-process in Stellar Nucleosynthesis and on the equation of state of neutron-rich matter—is discussed.
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precision mass measurements of 129 131cd and their impact on Stellar Nucleosynthesis via the rapid neutron capture process
Physical Review Letters, 2015Co-Authors: D Atanasov, Stéphane Goriely, P Ascher, Klaus Blaum, R B Cakirli, T E Cocolios, S George, F Herfurth, Hansthomas Janka, Oliver JustAbstract:Masses adjacent to the classical waiting-point nuclide ^{130}Cd have been measured by using the Penning-trap spectrometer ISOLTRAP at ISOLDE/CERN. We find a significant deviation of over 400 keV from earlier values evaluated by using nuclear beta-decay data. The new measurements show the reduction of the N=82 shell gap below the doubly magic ^{132}Sn. The Nucleosynthesis associated with the ejected wind from type-II supernovae as well as from compact object binary mergers is studied, by using state-of-the-art hydrodynamic simulations. We find a consistent and direct impact of the newly measured masses on the calculated abundances in the A=128-132 region and a reduction of the uncertainties from the precision mass input data.
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pygmy resonances and radiative nucleon captures for Stellar Nucleosynthesis
Physical Review C, 2015Co-Authors: N Tsoneva, Stéphane Goriely, Horst Lenske, R SchwengnerAbstract:The impact of low-energy multipole excitations and pygmy resonances on radiative neutron and proton-capture cross sections in nuclei close to the $\ensuremath{\beta}$-stability line is investigated. For this purpose, a microscopic theoretical approach based on self-consistent density functional theory and quasiparticle-random-phase-approximation formalism extended with multiphonon degrees of freedom is implemented in a statistical reaction model. The advantage of the method is the microscopic nuclear structure input for unified description of low-energy multiphonon excitations and pygmy and giant resonances. This is found to be important for the understanding of the fine structure and dynamics of the nuclear response function at low energies, which strongly influences nuclear reaction rates of astrophysical relevance. Calculations of the radiative capture cross sections of the reactions $^{85}\mathrm{Kr}(n,\ensuremath{\gamma})^{86}\mathrm{Kr}, ^{87}\mathrm{Sr}(n,\ensuremath{\gamma})^{88}\mathrm{Sr}$, and $^{89}\mathrm{Y}(p,\ensuremath{\gamma})^{90}\mathrm{Zr}$ are discussed in comparison with experimental data. For the reactions $^{89}\mathrm{Zr}(n,\ensuremath{\gamma})^{90}\mathrm{Zr}$ and $^{91}\mathrm{Mo}(n,\ensuremath{\gamma})^{92}\mathrm{Mo}$ theoretical predictions of the reaction cross sections are made.
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Nucleosynthesis: a field with still many open nuclear physics questions
Capture Gamma-Ray Spectroscopy and Related Topics, 2013Co-Authors: Stéphane GorielyAbstract:Stellar Nucleosynthesis is a vastly interdisciplinary field. There is a large number of different problems invoked calling for a variety of different and complementary research fields. Impressive progress has been made in the last decades in the various fields related to Nucleosynthesis, especially experimental and theoretical nuclear physics, as well as in groundor space-based astronomical observations and astrophysical modelings. In spite of that success, major problems and puzzles remain. The three major Nucleosynthesis processes called for to explain the origin of the elements heavier than iron are described and the major pending questions discussed. As far as nuclear physics is concerned, good quality nuclear data is known to be a necessary condition for a reliable model-ling of Stellar Nucleosynthesis. Through some specific examples, the need for further theoretical or experimental developments is also critically discussed in view of their impact on Nucleosynthesis predictions.
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the r process of Stellar Nucleosynthesis astrophysics and nuclear physics achievements and mysteries
Physics Reports, 2007Co-Authors: Marcel Arnould, Stéphane Goriely, Kohji TakahashiAbstract:Abstract The r-process, or the rapid neutron-capture process, of Stellar Nucleosynthesis is called for to explain the production of the stable (and some long-lived radioactive) neutron-rich nuclides heavier than iron that are observed in stars of various metallicities, as well as in the solar system. A very large amount of nuclear information is necessary in order to model the r-process. This concerns the static characteristics of a large variety of light to heavy nuclei between the valley of stability and the vicinity of the neutron-drip line, as well as their beta-decay branches or their reactivity. Fission probabilities of very neutron-rich actinides have also to be known in order to determine the most massive nuclei that have a chance to be involved in the r-process. Even the properties of asymmetric nuclear matter may enter the problem. The enormously challenging experimental and theoretical task imposed by all these requirements is reviewed, and the state-of-the-art development in the field is presented. Nuclear-physics-based and astrophysics-free r-process models of different levels of sophistication have been constructed over the years. We review their merits and their shortcomings. The ultimate goal of r-process studies is clearly to identify realistic sites for the development of the r-process. Here too, the challenge is enormous, and the solution still eludes us. For long, the core collapse supernova of massive stars has been envisioned as the privileged r-process location. We present a brief summary of the one- or multidimensional spherical or non-spherical explosion simulations available to-date. Their predictions are confronted with the requirements imposed to obtain an r-process. The possibility of r-nuclide synthesis during the decompression of the matter of neutron stars following their merging is also discussed. Given the uncertainties remaining on the astrophysical r-process site and on the involved nuclear physics, any confrontation between predicted r-process yields and observed abundances is clearly risky. A comparison dealing with observed r-nuclide abundances in very metal-poor stars and in the solar system is attempted on grounds of r-process models based on parametrised astrophysics conditions. The virtues of the r-process product actinides for dating old stars or the solar system are also critically reviewed.
G J Wasserburg - One of the best experts on this subject based on the ideXlab platform.
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isotopic systematics of presolar silicon carbide from the orgueil ci chondrite implications for solar system formation and Stellar Nucleosynthesis
Geochimica et Cosmochimica Acta, 1997Co-Authors: G R Huss, I D Hutcheon, G J WasserburgAbstract:One hundred and forty individual SiC grains (1-9.6 µm) and twenty-two grain aggregates (2.3-7.8 µm) from the Orgueil (CI) chondrite have been measured by ion microprobe. Silicon and carbon isotopic data were obtained for all individual grains and aggregates, and nitrogen, magnesium, and aluminum abundances and isotopic compositions were measured for most grains and aggregates. Abundances of lithium, beryllium, boron, and sodium were measured for some individual grains. Orgueil SiC is remarkably similar to Murchison K-series SiC in the ranges and distributions of silicon and carbon isotopic compositions, the initial abundances of ^(26)AI, the abundances of minor and trace elements, and the proportions of isotopically unusual grains. Higher ^(15)N/^(14)N ratios in 1-4/µm Murchison K-series SiC grains relative to similar-sized Orgueil grains are inferred to be due to higher amounts of terrestrial nitrogen in the Murchison samples. Higher ^(15)N/^(14)N ratios in 3-6 µm Murchison KJH SiC grains cannot be explained by terrestrial nitrogen and imply that larger SiC grains sampled a different population of parent stars. SiC aggregates have different average silicon and carbon compositions than individual grains, indicating different source stars for the 0.1-1 µm constituent grains. However, the aggregates probably formed by clumping of small grains during laboratory procedures, not at the Stellar source. Differences between Murchison L-series SiC and SiC from Murchison K-series and Orgueil are due to the presence of terrestrial SiC among L-series grains and to the larger average grain size of L-series SiC. When terrestrial contamination, sample size, and grain size are taken into account, there is no evidence of an intrinsic difference between Orgueil and Murchison SiC. The Orgueil data provide new information about Stellar Nucleosynthesis and the SiC parent stars. Carbon and nitrogen isotopic compositions indicate that nuclear processing in addition to that described by most Stellar models occurs below the convective Stellar envelope during the Red Giant and AGB phases (Cool Bottom Processing). Grains with high ^(15)N/^(14)N but with other characteristics consistent with AGB source stars indicate that ^(15)N is produced in AGB stars, contrary to the predictions of the standard models. A significantly higher rate for the ^(18)O(ɑ,n)^(15)N reaction than is typically used might reconcile the models with the observations. No data currently rule out a higher reaction rate. Addition of ^(18)O produced via ^(14)N(ɑ, y)^(18)O below the hydrogen shell and burned to ^(15)N in the envelope may also play a role in producing the high ^(15)N/^(14)N ratios observed in some SiC grains. Following previous workers, we take the slope ~2.2 silicon isotope array defined by mainstream SiC grains to reflect the initial compositions of the parent stars due to galactic evolution. A general correlation between ^(12)C/^(13)C and ^(29'30)Si/^(28)Si and more scatter around the silicon array at low ^(29'30)Si/^(28)Si indicate that SiC grains with higher ^(29'30)Si/^(28)Si ratios come from higher-metallicity parent stars. A lack of resolved isotopic effects in ^(25)Mg/^(24)Mg suggests that variations in initial magnesium compositions of the parent stars are at least a factor of three smaller than those in silicon and that the ^(22)Ne neutron source was not significantly activated in the AGB stars that produced SiC grains, in accord with theory. These observations indicate that the parent stars of most mainstream SiC grains were ≤2.3 M_☉ and experienced enough Third Dredge-up thermal pulses to supply their envelopes with 2-3% helium.shell material. A few grains have characteristics suggesting that they came from more-massive stars. Most parent stars of > 1 µm SiC grains apparently had metallicities higher than that of the sun.
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oxygen isotopes in circumStellar al203 grains from meteorites and Stellar Nucleosynthesis
The Astrophysical Journal, 1994Co-Authors: G R Huss, R Gallino, Albert J Fahey, G J WasserburgAbstract:We have found a ~3 µm Al_2O_3 grain (B39) in the Bishunpur LL3.1 chondrite that is enriched in ^(17)O by a factor of ~ 6.8 (^(16)O/^(17)O = 385 ± 9) and depleted in 180 by almost 60% (^(16)O/^(18)O = 853 ± 30) relative to solar system oxygen and has an initial ^(26)Al/^(27)Al = 1.7 ± 0.2 x 10^3, ~34 times greater than the initial solar system value. The isotopic compositions of B39 and two other Al_2O_3 grains previously reported from the Orgueil and Murchison meteorites show that these grains formed directly from the ejecta of low-mass AGB stars with C/0 < 1. A simple theoretical analysis is presented showing that the oxygen systematics of the grains are a natural consequence of main-sequence evolution followed by first dredge-up. ^(26)AI is the result of third dredge-up. CircumStellar Al_2O_3 grains provide very precise isotopic data for Stellar ejecta that complement spectroscopic observations of oxygen-rich stars. Isotopic differences indicate that the Al_2O_3 grains come from separate stars of different mass and initial oxygen composition that originated in molecular clouds different from the one in which the solar system formed.
M Geha - One of the best experts on this subject based on the ideXlab platform.
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chemical analysis of the ultrafaint dwarf galaxy grus ii signature of high mass Stellar Nucleosynthesis
The Astrophysical Journal, 2020Co-Authors: Terese T Hansen, J L Marshall, J D Simon, R A Bernstein, A B Pace, P S Ferguson, D Q Nagasawa, K Kuehn, D Carollo, M GehaAbstract:We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultrafaint dwarf (UFD) galaxy Grus II. All stars exhibit a higher than expected [Mg/Ca] ratio compared to metal-poor stars in other UFD galaxies and in the Milky Way (MW) halo. Nucleosynthesis in high-mass ($\geqslant $ 20 M ⊙) core-collapse supernovae has been shown to create this signature. The abundances of this small sample (three) stars suggests the chemical enrichment of Grus II could have occurred through substantial high-mass Stellar evolution, and is consistent with the framework of a top-heavy initial mass function. However, with only three stars it cannot be ruled out that the abundance pattern is the result of a stochastic chemical enrichment at early times in the galaxy. The most metal-rich of the three stars also possesses a small enhancement in rapid neutron-capture (r-process) elements. The abundance pattern of the r-process elements in this star matches the scaled r-process pattern of the solar system and r-process enhanced stars in other dwarf galaxies and in the MW halo, hinting at a common origin for these elements across a range of environments. All current proposed astrophysical sites of r-process element production are associated with high-mass stars, thus the possible top-heavy initial mass function of Grus II would increase the likelihood of any of these events occurring. The time delay between the α and r-process element enrichment of the galaxy favors a neutron star merger as the origin of the r-process elements in Grus II.
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chemical analysis of the ultra faint dwarf galaxy grus ii signature of high mass Stellar Nucleosynthesis
arXiv: Solar and Stellar Astrophysics, 2020Co-Authors: Terese T Hansen, J L Marshall, J D Simon, R A Bernstein, A B Pace, D Q Nagasawa, K Kuehn, D Carollo, P Ferguson, M GehaAbstract:We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultra-faint dwarf galaxy Grus~II. All stars exhibit a higher than expected $\mathrm{[Mg/Ca]}$ ratio compared to metal-poor stars in other ultra-faint dwarf galaxies and in the Milky Way halo. Nucleosynthesis in high mass ($\geqslant 20$M$_\odot$) core-collapse supernovae has been shown to create this signature. The abundances of this small sample (3) stars suggest the chemical enrichment of Grus~II could have occurred through substantial high-mass Stellar evolution and is consistent with the framework of a top-heavy initial mass function. However, with only three stars it can not be ruled out that the abundance pattern is the result of a stochastic chemical enrichment at early times in the galaxy. The most metal-rich of the three stars also possesses a small enhancement in rapid neutron-capture ($r$-process) elements. The abundance pattern of the $r$-process elements in this star matches the scaled $r$-process pattern of the solar system and $r$-process enhanced stars in other dwarf galaxies and in the Milky Way halo, hinting at a common origin for these elements across a range of environments. All current proposed astrophysical sites of $r$-process element production are associated with high-mass stars, thus the possible top-heavy initial mass function of Grus~II would increase the likelihood of any of these events occurring. The time delay between the $\alpha$ and $r$-process element enrichment of the galaxy favors a neutron star merger as the origin of the $r$-process elements in Grus~II.
