scholarly journals An increase in the 12C+12C fusion rate from resonances at astrophysical energies

2019 ◽  
Vol 52 (382) ◽  
pp. MISC6-MISC8
Author(s):  
Aurora Tumino
Keyword(s):  
Neutron Stars ◽  
Cross Sections ◽  
Coulomb Barrier ◽  
Reaction Rate ◽  
Nuclear Reactions ◽  
Massive Stars ◽  
Reaction Rates ◽  
Fusion Reactions ◽  
Trojan Horse Method ◽  
Carbon Burning

Carbon burning powers pivotal scenarios that influence the fate of stars, such as the late evolutionary stages of massive stars (exceeding eight solar masses), superbursts from accreting neutron stars and progenitors of Type Ia supernovae. It proceeds through the 12C+12C fusion reactions that produce an \( \alpha \) particle and neon-20 or a proton and sodium-23 —that is, 12C(12C, \( \alpha \) )20Ne and 12C(12C, \( p \))23Na— at temperatures greater than \( 0.4 \cdot 10^9 \) K, corresponding to astrophysical energies exceeding a megaelectronvolt (MeV), at which such nuclear reactions are more likely to occur in stars. The cross-sections for those carbon fusion reactions (probabilities that are required to calculate the rate of the reactions) have never been measured below 2 MeV because of exponential suppression arising from the Coulomb barrier (the Coulomb barrier is around 6 MeV). The reference rate at temperatures below \( 1.2\cdot 10^9 \) K relies on extrapolations that ignore the effects of possible low-lying resonances. In Tumino et al. (2018), we report the measurement of the 12C(12C, \( \alpha_{0,1} \)) 20Ne and 12C(12C, \( p_{0,1} \)) 23Na reaction rates (where the subscripts 0 and 1 stand for the ground and first excited states of 20Ne and 23Na, respectively) at centre-of-mass energies from 2.7 to 0.8 MeV using the Trojan Horse method and the deuteron in 14N. This is an indirect technique aiming at measuring low-energy nuclear reactions unhindered by the Coulomb barrier and free of electron screening. The deduced cross-sections exhibit several resonances that are responsible for a very large increase of the reaction rate at the relevant temperatures. In particular, around \( 5\cdot 10^8 \) K, the reaction rate is more than 25 times larger than the reference value. This finding may have significant implications such as lowering the temperatures and densities required for the ignition of carbon burning in massive stars and decreasing the superburst ignition depth in accreting neutron stars in the direction to reconcile observations with theoretical models.

Investigation of Sub-Coulomb barrier fusion reaction of α +40Ca in different models

2017 ◽  
Vol 26 (12) ◽  
pp. 1750086 ◽  
Author(s):  
F. Koyuncu ◽  
A. Soylu
Keyword(s):  
Cross Sections ◽  
Coulomb Barrier ◽  
Reaction Rate ◽  
Fusion Reaction ◽  
Reaction Rates ◽  
Nucleon Nucleon ◽  
Talys Code ◽  
Comparative Results ◽  
Double Folding ◽  
Energy Dependent

In this study, microscopic nucleon–nucleon Double Folding (DF) and phenomenological potentials have been used to investigate [Formula: see text]Ca reaction observables at sub-barrier energies. In the calculations, semi-classical Wentzel–Kramers–Brillouin (WKB) approach has been used in order to obtain the cross-sections and reaction rates of [Formula: see text]Ca. Besides WKB approximation, we have also utilized Talys code in order to get the comparative results and find out the method differences. To estimate the reaction rates, energy-dependent cross-sections and astrophysical S-factors of [Formula: see text]+[Formula: see text]Ca have been used. Herewith, differences between models and potentials have been demonstrated using the reaction rate estimates.

ABUNDANCE ANOMALIES PRODUCED BY NUCLEAR REACTIONS IN STELLAR SURFACE LAYERS: I. NUCLEAR-REACTION RATES

1967 ◽  
Vol 45 (10) ◽  
pp. 3275-3296 ◽  
Author(s):  
P. J. Brancazio ◽  
A. Gilbert ◽  
A. G. W. Cameron
Keyword(s):  
Statistical Theory ◽  
Nuclear Reaction ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Level Density ◽  
Preliminary Investigation ◽  
Computer Time ◽  
Reaction Rates ◽  
Reaction Cross ◽  
Surface Layers

A preliminary investigation of the effects on abundances in stellar surfaces of extensive nuclear bombardment required the calculation of more than 105 nuclear-reaction cross sections. It was necessary to develop simplified methods for using the statistical theory of nuclear reactions to make these calculations in order that the computer time should not be prohibitive. These methods are described here and the results are compared with experiment. The accuracy of the calculations is, in general, about as good as, or somewhat better than, that obtained in previous applications of the statistical theory, probably because the use of an accurate level density formula outweighed the crudity of other approximations.

scholarly journals Global predictions for astrophysics applications

2020 ◽  
Vol 13 ◽  
pp. 18
Author(s):  
P. Demetriou
Keyword(s):  
Nuclear Reaction ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Nuclear Astrophysics ◽  
Reaction Network ◽  
Reaction Rates ◽  
Reaction Cross ◽  
Hartree Fock ◽  
Microscopic Models ◽  
The Stability

Nuclear reaction rates play a crucial role in nuclear astrophysics. In the last decades there has been an enormous effort to measure reaction cross sections and extensive experimental databases have been compiled as a result. In spite of these efforts, most nuclear reaction network calculations still have to rely on theoretical predic- tions of experimentally unknown rates. In particular, in astrophysics applications such as the s-, r- and p-process nucleosynthesis involving a large number of nuclei and nuclear reactions (thousands). Moreover, most of the ingredients of the cal- culations of reaction rates have to be extrapolated to energy and/or mass regions that cannot be explored experimentally. For this reason it is important to develop global microscopic or semi-microscopic models of nuclear properties that give an accurate description of existing data and are reliable for predictions far away from the stability line. The need for more microscopic input parameters has led to new devel- opments within the Hartree-Fock-Bogoliubov method, some of which are presented in this paper.

Calculation of fusion rates at extremely low energies in laser plasmas

2010 ◽  
Vol 6 (S274) ◽  
pp. 44-47 ◽  
Author(s):  
D. Mascali ◽  
N. Gambino ◽  
S. Tudisco ◽  
A. Anzalone ◽  
A. Bonanno ◽  
...  
Keyword(s):  
Nuclear Reactions ◽  
Fusion Reaction ◽  
Reaction Rates ◽  
Debye Screening ◽  
Fusion Reactions ◽  
Plasma Dynamics ◽  
Laser Plasmas ◽  
Low Energies ◽  
Screening Factor ◽  
The One

AbstractAt temperatures and densities that are typical of plasmas produced by lasers pulses interacting with solid targets, at power intensities I > 1012W/cm2, the classical Debye screening factor in nuclear reactions becomes comparable with the one of the solar core. Preliminary calculations about the total number of fusion reactions have been performed following an hydrodynamical approach for the description of the plasma dynamics. This approach is propaedeutic for future measurements of D-D fusion reaction rates.

scholarly journals Screening effects on resonant thermonuclear reaction rates

2019 ◽  
Vol 11 ◽  
Author(s):  
T. Liolios ◽  
K. Langanke ◽  
W. Wiescher
Keyword(s):  
Reaction Rate ◽  
Nuclear Reactions ◽  
Reaction Network ◽  
Reaction Rates ◽  
Partial Width ◽  
Entrance Channel ◽  
Correction Factors ◽  
Thermonuclear Reaction ◽  
Hydrogen Burning ◽  
Stellar Reaction Rate

The reaction rate of several astrophysically important nuclear reactions is dominated by the contribution of narrow resonances at the astrophysically most effective energies. In the stellar plasma the partial width of the resonances in the entrance channel is modified due to screening corrections. This effect, so far ignored in stellar reaction network calculations, reduces the conventional Salpeterscreening enhancement of the reaction rate. We derive analytical screening correction factors for the contributions of narrow resonances to the stellar reaction rate and discuss the effects for UC (a, j)lsO, 150(a,7)19 Ne and other reactions of relevance to explosive hydrogen burning

scholarly journals A systematic study of proton capture reactions in the Se-Sn region relevant to p-process nucleosynthesis

2019 ◽  
Vol 11 ◽  
Author(s):  
S. Harissopulos ◽  
P. Demetriou ◽  
S. Galanopoulos ◽  
G. Kriembardis ◽  
M. Kokkoris ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Nuclear Physics ◽  
Nuclear Reactions ◽  
Reaction Network ◽  
Reaction Rates ◽  
Compton Suppression ◽  
Experimental Information ◽  
Systematic Investigation ◽  
Model Calculations

The synthesis of the so-called ρ nuclei, i.e. a certain class of proton rich nuclei that are heavier than iron, requires a special mechanism known as ρ process. This process consists of various nucleosynthetic scenaria. In some of them proton and alpha-capture reactions are strongly involved, p-process nucleosynthesis is assumed to occur in the Oxygen/Neon rich layers of type II supernovae during their explosion, ρ nuclei are typically 10-100 times less abundant than the corresponding more neutron-rich isotopes. The prediction of their abundances is one of the major puzzles of all models of p-process nucleosynthesis. Until now all these models are capable of reproducing these abundances within a factor of 3. However, they all fail in the case of the light ρ nuclei with A<100. The observed discrepancies could be attributed to uncertainties in the pure "astrophysical" part of the p-process modelling. However, they could also be the result of uncertainties in the nuclear physics data entering the corresponding abundance calculations. In order to perform these calculations the cross sections of typically 10000 nuclear reactions of an extended reaction network involving almost 1000 nuclei from A=12 to 210 are used as input data. Such a huge amount of experimental cross section data are not available. Hence, all extended network calculations rely almost completely on cross sections predicted by the Hauser-Feshbach (HF) theory. It is therefore of paramount importance, on top of any astrophysical model improvements, to test also the reliability of the HF calculations, i.e. to investigate the uncertainties associated with the evaluation of the nuclear properties, like nuclear level densities and nucleon-nucleus potentials, entering the calculations. Until now, this check has been hindered significantly by the fact that in the Se-Sn region there has been scarce experimental information on cross sections at astrophysically relevant energies. In the present work, a systematic investigation of (p,7) cross sections of nuclei from Se to Sb is presented for the first time. The in-beam cross section measurements reported were carried out at energies relevant to p-process nucleosynthesis, i.e. from 1.4 to 5 MeV. The experiments were performed by using either an array of 4 HPGe detectors of 100% relative efficiency shielded with BGO crustals for Compton suppression, or a 4π Nal summing detector. The resulting cross sections, astrophysical S-factors and reaction rates of more than 10 nuclear reactions are compared with the predictions of various statistical model calculations.

scholarly journals Massive Star Modeling and Nucleosynthesis

2021 ◽  
Vol 8 ◽  
Author(s):  
Sylvia Ekström
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Massive Star ◽  
Nuclear Reactions ◽  
Massive Stars ◽  
Reaction Rates ◽  
Star Evolution ◽  
Structural Impact ◽  
Massive Star Evolution ◽  
The Impact

After a brief introduction to stellar modeling, the main lines of massive star evolution are reviewed, with a focus on the nuclear reactions from which the star gets the needed energy to counterbalance its gravity. The different burning phases are described, as well as the structural impact they have on the star. Some general effects on stellar evolution of uncertainties in the reaction rates are presented, with more precise examples taken from the uncertainties of the 12C(α, γ)16O reaction and the sensitivity of the s-process on many rates. The changes in the evolution of massive stars brought by low or zero metallicity are reviewed. The impact of convection, rotation, mass loss, and binarity on massive star evolution is reviewed, with a focus on the effect they have on the global nucleosynthetic products of the stars.

scholarly journals Nuclear physics and its role for describing the early universe

2019 ◽  
Vol 49 ◽  
pp. 1960012 ◽  
Author(s):  
R. G. Pizzone ◽  
R. Spartá ◽  
M. La Cognata ◽  
L. Lamia ◽  
C. Spitaleri ◽  
...  
Keyword(s):  
Cross Sections ◽  
Nuclear Physics ◽  
Reaction Rates ◽  
Big Bang ◽  
Abundance Estimates ◽  
Bare Nucleus ◽  
Trojan Horse Method ◽  
Direct Cross ◽  
Primordial Abundance ◽  
Temperature Ranges

Big Bang Nucleosynthesis (BBN) requires several nuclear physics inputs and nuclear reaction rates. An up-to-date compilation of direct cross sections of [Formula: see text], [Formula: see text]He and [Formula: see text]He reactions is given, being these ones among the most uncertain bare-nucleus cross sections. An intense experimental effort has been carried on in the last decade to apply the Trojan Horse Method (THM) to study reactions of relevance for the BBN and measure their astrophysical S(E)-factor. The reaction rates and the relative error for the four reactions of interest are then numerically calculated in the temperature ranges of relevance for BBN [Formula: see text]. These value were then used as input physics for primordial nucleosynthesis calculations in order to evaluate their impact on the calculated primordial abundances and isotopical composition for H, He and Li. New results on the [Formula: see text]He reaction rate were also taken into account.These were compared with the observational primordial abundance estimates in different astrophysical sites. Reactions to be studied in perspective will also be discussed.

scholarly journals Effect of Excited States on Thermonuclear Reaction Rates

1983 ◽  
Vol 36 (4) ◽  
pp. 583 ◽  
Author(s):  
DG Sargood
Keyword(s):  
Statistical Model ◽  
Excited States ◽  
Cross Sections ◽  
Reaction Rate ◽  
Ground States ◽  
Reaction Rates ◽  
Thermonuclear Reaction ◽  
Thermal Distribution ◽  
Naturally Occurring ◽  
Thermonuclear Reaction Rate

Values of the ratio of the thermonuclear reaction rate of a reaction, with target nuclei in a thermal distribution of energy states, to the reaction rate with all target nuclei in their ground states are tabulated for neutron, proton and (X-particle induced reactions on the naturally occurring nuclei from 2�Ne to 70Zn, at temperatures of 1, 2, 3�5 and 5 x 109 K. The ratios are determined from reaction rates based on statistical model cross sections.

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