Thermonuclear Reactions and Nuclear Reactions in Stellar Interiors

1981 ◽

Vol 300 (1456) ◽

pp. 641-648

Keyword(s):

Nuclear Reactions ◽

Pauli Exclusion Principle ◽

Significant Rise ◽

Exclusion Principle ◽

Reaction Products ◽

Thermonuclear Reactions ◽

Radiated Energy ◽

Large Numbers ◽

Stellar Interiors ◽

Late Stages

Thermonuclear reactions provide the main source of radiated energy for stars and they are also believed to be responsible for the production of most of the heavy elements in the Universe. The thermonuclear plasma is confined by the force of gravitation and for most of a star’s history the reactions occur slowly and steadily. In some circumstances, the properties of a star change very rapidly and explosive nuclear reactions occur. In very dense stellar interiors the energy states available to electrons may be limited by the Pauli exclusion principle. When thermonuclear reactions start in such a degenerate gas, a rise in temperature is not accompanied by a significant rise in pressure and as a result there may be a runaway increase in reaction rate. In contrast, when reactions start in a non-degenerate gas, there is normally an effective thermostat. A star is usually opaque to reaction products, so that there is no problem in maintaining the reaction temperature, but at late stages of stellar evolution nuclear or elementary particle reactions may produce large numbers of neutrinos and antineutrinos that do escape.

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Physical mechanisms of mixing in stellar interiors

Symposium - International Astronomical Union ◽

10.1017/s0074180900031363 ◽

1984 ◽

Vol 105 ◽

pp. 491-512

Author(s):

Evry Schatzman

Keyword(s):

Diffusion Equation ◽

Stellar Evolution ◽

Turbulent Mixing ◽

Nuclear Reactions ◽

Chemical Elements ◽

Solar Neutrinos ◽

Stellar Structure ◽

Physical Mechanisms ◽

Nitrogen Abundance ◽

Stellar Interiors

The different mechanisms by which mixing can take place in stellar interiors are considered : the classical Rayleigh-Benard instability with penetrative convection and over-shooting, semi-convection, gravitationnal and radiative settling, turbulent mixing. The latter mechanism is thoroughly described, from the driving force of turbulent mixing to its influence on stellar structure, stellar evolution and the analysis of the corresponding observationnal data.Turbulent mixing has to be considered each time the building up of a concentration gradient takes place, either by gravitationnal or radiative settling or by nuclear reactions. Turbulent mixing, as a first approximation, can be described by an isotropic diffusion coefficient. The process is then governed by a diffusion equation. The behaviour of the solution of the diffusion equation needs some explanation in order to be well understood.A number of examples concerning surface abundances of chemical elements are given (3He, 7Li, Be, 12C, 13C, 14N), as well as a discussion of the solar neutrinos problem.The building up of a µ-barrier, which stops the turbulence allows stellar evolution towards the giant branch and explains nitrogen abundance at the surface of giants of the first ascending branch.Turbulent mixing is also of some importance for the transfer of angular momentum and has to be taken into account for explaining the abundance of the elements in Wolf-Rayet stars.

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Mixing in Starts

Science ◽

10.1126/science.240.4860.1743 ◽

1988 ◽

Vol 240 (4860) ◽

pp. 1743-1743 ◽

Cited By ~ 10

Author(s):

George Wallerstein

Keyword(s):

Mass Transfer ◽

Isotopic Composition ◽

Mass Loss ◽

Nuclear Reactions ◽

Stellar Surface ◽

Surface Mass ◽

Stellar Interiors

Analysis of the chemical and isotopic composition of stellar surfaces reveals the types of nuclear reactions that have occurred in the stellar interiors as well as the timing and depths from which material once deep in the star has reached the surface. Mass loss from the stellar surface and, in some cases, mass transfer from a companion enhance the opportunity to observe material that is the product of internal nuclear reactions. Detailed studies show substantial deficiencies in current models with the timing and depth of convective and other forms of mixing.

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Nuclear reactions in stars

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1961.0023 ◽

1961 ◽

Vol 260 (1301) ◽

pp. 170-175 ◽

Cited By ~ 2

Keyword(s):

Stellar Evolution ◽

Nuclear Reactions ◽

Thermonuclear Reactions ◽

Stellar Energy

Thermonuclear reactions important for the generation of stellar energy during different phases of stellar evolution are discussed.

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Carbon and oxygen abundances in dwarf stars of the Solar neighbourhood

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318008499 ◽

2018 ◽

Vol 14 (S345) ◽

pp. 265-266

Author(s):

G. Tautvaišienė ◽

R. Minkevičiūtė ◽

E. Stonkutė ◽

A. Drazdauskas ◽

Š. Mikolaitis

Keyword(s):

Water Availability ◽

Space Missions ◽

Solar Neighbourhood ◽

Dwarf Stars ◽

Thermonuclear Reactions ◽

First Results ◽

Stellar Interiors

AbstractStars and planets form from the same material, thus some of their properties are expected to be inter-connected. In order to characterise exoplanets, we need to investigate the planet-hosting stars. Carbon and oxygen are quite abundant and play an important role in stellar interiors by generating energy in thermonuclear reactions. Abundances of C and O may influence water availability on exoplanets. The C/O ratio also controls an amount of carbides and silicates that can be formed. Thus, we are performing a uniform study of C/O ratios in bright stars ( V < mag) located towards the northern ecliptic pole which will be targeted by the TESS and JWST space missions. The first results for a sample of 140 stars analysed are presented.

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Nuclear Processes Related to the Ap Stars and the Heaviest Chemical Elements

International Astronomical Union Colloquium ◽

10.1017/s0252921100080520 ◽

1976 ◽

Vol 32 ◽

pp. 169-182

Author(s):

B. Kuchowicz

Keyword(s):

Nuclear Physics ◽

Nuclear Reactions ◽

Chemical Elements ◽

Fission Products ◽

Abundance Pattern ◽

Isotopic Shifts ◽

Processed Material ◽

R Process ◽

Ap Stars ◽

Nuclear Processes

SummaryIsotopic shifts in the lines of the heavy elements in Ap stars, and the characteristic abundance pattern of these elements point to the fact that we are observing mainly the products of rapid neutron capture. The peculiar A stars may be treated as the show windows for the products of a recent r-process in their neighbourhood. This process can be located either in Supernovae exploding in a binary system in which the present Ap stars were secondaries, or in Supernovae exploding in young clusters. Secondary processes, e.g. spontaneous fission or nuclear reactions with highly abundant fission products, may occur further with the r-processed material in the surface of the Ap stars. The role of these stars to the theory of nucleosynthesis and to nuclear physics is emphasized.

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Nuclear Reactions in Deuterium Titanium

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100134260 ◽

1990 ◽

Vol 48 (2) ◽

pp. 134-135

Author(s):

D.M. Vanderwalker

Keyword(s):

Nuclear Reactions ◽

Ion Beam ◽

Exothermic Reaction ◽

Pure Titanium ◽

Fundamental Interest ◽

Transmission Electron ◽

Iodide Titanium ◽

A Cell ◽

After Hours ◽

Quantity Of Heat

There is a fundamental interest in electrochemical fusion of deuterium in palladium and titanium since its supposed discovery by Fleischmann and Pons. Their calorimetric experiments reveal that a large quantity of heat is released by Pd after hours in a cell, suggesting fusion occurs. They cannot explain fusion by force arguments, nor can it be an exothermic reaction on the formation of deuterides because a smaller quantity of heat is released. This study examines reactions of deuterium in titanium.Both iodide titanium and 99% pure titanium samples were encapsulated in vacuum tubes, annealed for 2h at 800 °C. The Ti foils were charged with deuterium in a D2SO4 D2O solution at a potential of .45V with respect to a calomel reference junction. Samples were ion beam thinned for transmission electron microscopy. The TEM was performed on the JEOL 200CX.The structure of D charged titanium is α-Ti with hexagonal and fee deuterides.

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The evolution of the microstructure of 600 Mev proton irradiated materials

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100178148 ◽

1990 ◽

Vol 48 (4) ◽

pp. 1002-1003

Author(s):

R. Gotthardt ◽

A. Horsewell ◽

F. Paschoud ◽

S. Proennecke ◽

M. Victoria

Keyword(s):

Nuclear Reactions ◽

Dislocation Loops ◽

Defect Clusters ◽

Weak Beam ◽

Stacking Fault Tetrahedra ◽

Small Defect ◽

Sufficient Intensity ◽

Reactor Materials ◽

Metallic Impurities ◽

Beam Technique

Fusion reactor materials will be damaged by an intense field of energetic neutrons. There is no neutron source of sufficient intensity at these energies available at present, so the material properties are being correlated with those obtained in irradiation with other irradiation sorces. Irradiation with 600 MeV protons produces both displacement damage and impurities due to nuclear reactions. Helium and hydrogen are produced as gaseous impurities. Other metallic impurities are also created . The main elements of the microstructure observed after irradiation in the PIREX facility, are described in the following paragraphs.A. Defect clusters at low irradiation doses: In specimens irradiated to very low doses (1021-1024 protons.m-2), so that there is no superimposition of contrast, small defect clusters have been observed by the weak beam technique. Detailed analysis of the visible contrast (>0.5 nm diameter) revealed the presence of stacking fault tetrahedra, dislocation loops and a certain number of unidentified clusters . Typical results in Cu and Au are shown in Fig. 1.

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