scholarly journals REACTION RATES AND NUCLEAR PROPERTIES RELEVANT FOR NUCLEOSYNTHESIS IN MASSIVE STARS AND FAR FROM STABILITY

2003 ◽  
Author(s):  
T. RAUSCHER ◽  
C. FRÖHLICH ◽  
K. H. GUBER
Keyword(s):  
Massive Stars ◽  
Reaction Rates

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.

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.

Reaction rates for O-18(alpha, gamma)Ne-22, Ne-22(alpha, gamma)Mg-26, and Ne-22(alpha, n)Mg-25 in stellar helium burning and s-process nucleosynthesis in massive stars

1994 ◽  
Vol 437 ◽  
pp. 396 ◽  
Author(s):  
F. Kaeppeler ◽  
M. Wiescher ◽  
U. Giesen ◽  
J. Goerres ◽  
I. Baraffe ◽  
...  
Keyword(s):  
Massive Stars ◽  
Reaction Rates ◽  
Helium Burning ◽  
O 18

The Study of 12C(α, γ7)16O in massive stars at explosive conditions

2005 ◽  
Vol 201 ◽  
pp. 453-454
Author(s):  
Kalpana. Duorah ◽  
Aditi. Bezbarua
Keyword(s):  
High Temperature ◽  
Mass Formula ◽  
Massive Star ◽  
Massive Stars ◽  
Reaction Rates ◽  
Surface Binding ◽  
Temperature Dependent ◽  
Thermonuclear Burning ◽  
Nuclear Masses ◽  
Semi Empirical

Massive stars (M ≥ 10M⊙) and supernova are found to be the possible sites for explosive thermonuclear burning. When a massive star collapses, shock waves moving through various convective zones produces explosive situations. The gravitational collapse of a helium exhausted core leads to violent instabilities. The reaction 12C(α, γ)16O is being studied under this condition. Recently it has been found that the coefficients in the semi-empirical mass formula are temperature dependent. Assuming the volume and surface binding to be effective, the nuclear masses, Q values, and reaction rates are calculated. Carbon alpha reaction is found to attain explosive proportion at the high temperature range considered here.

SEM analysis of the change in the reaction rates with deposit structures in the copper-iron cementation system

1978 ◽  
Vol 36 (1) ◽  
pp. 456-457
Author(s):  
V. Annamalai ◽  
L.E. Murr
Keyword(s):  
Structural Characteristics ◽  
Secondary Electron Emission ◽  
Copper Deposit ◽  
Reaction Rates ◽  
Sem Analysis ◽  
Experimental Conditions ◽  
Major Drawback ◽  
Emission Mode ◽  
Scrap Iron ◽  
Image Position

Economical recovery of copper metal from leach liquors has been carried out by the simple process of cementing copper onto a suitable substrate metal, such as scrap-iron, since the 16th century. The process has, however, a major drawback of consuming more iron than stoichiometrically needed by the reaction.Therefore, many research groups started looking into the process more closely. Though it is accepted that the structural characteristics of the resultant copper deposit cause changes in reaction rates for various experimental conditions, not many systems have been systematically investigated. This paper examines the deposit structures and the kinetic data, and explains the correlations between them.A simple cementation cell along with rotating discs of pure iron (99.9%) were employed in this study to obtain the kinetic results The resultant copper deposits were studied in a Hitachi Perkin-Elmer HHS-2R scanning electron microscope operated at 25kV in the secondary electron emission mode.

The Effects of Nitrogen on Electrical and Structural Properties in TaSixNy/SiO2/p-Si MOS Capacitors

2002 ◽  
Vol 716 ◽  
Author(s):  
You-Seok Suh ◽  
Greg Heuss ◽  
Jae-Hoon Lee ◽  
Veena Misra
Keyword(s):  
Structural Properties ◽  
Electron Spectroscopy ◽  
Oxygen Diffusion ◽  
Gate Dielectric ◽  
Barrier Properties ◽  
Reaction Rates ◽  
Cross Sectional ◽  
Mos Capacitors ◽  
Transmission Electron ◽  
Thermal Stability Of

AbstractIn this work, we report the effects of nitrogen on electrical and structural properties in TaSixNy /SiO2/p-Si MOS capacitors. TaSixNy films with various compositions were deposited by reactive sputtering of TaSi2 or by co-sputtering of Ta and Si targets in argon and nitrogen ambient. TaSixNy films were characterized by Rutherford backscattering spectroscopy and Auger electron spectroscopy. It was found that the workfunction of TaSixNy (Si>Ta) with varying N contents ranges from 4.2 to 4.3 eV. Cross-sectional transmission electron microscopy shows no indication of interfacial reaction or crystallization in TaSixNy on SiO2, resulting in no significant increase of leakage current in the capacitor during annealing. It is believed that nitrogen retards reaction rates and improves the chemical-thermal stability of the gate-dielectric interface and oxygen diffusion barrier properties.

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