4.4.2.4 Nuclear burning phases in stars

2005 ◽  
pp. 75-89
Author(s):  
M. F. El Eid ◽  
C. de Loore
Keyword(s):  
Nuclear Burning

Small high temperature gas-cooled reactors with innovative nuclear burning

2008 ◽  
Vol 50 (2-6) ◽  
pp. 251-256 ◽  
Author(s):  
Peng Hong Liem ◽  
Ismail ◽  
Hiroshi Sekimoto
Keyword(s):  
High Temperature ◽  
Nuclear Burning ◽  
High Temperature Gas

scholarly journals Drifts of the marginally stable burning frequency in the X-ray binaries 4U 1608–52 and Aql X–1

2021 ◽  
Vol 502 (2) ◽  
pp. 1856-1863
Author(s):  
G C Mancuso ◽  
D Altamirano ◽  
M Méndez ◽  
M Lyu ◽  
J A Combi
Keyword(s):  
Frequency Drift ◽  
Soft Or ◽  
Significance Level ◽  
X Ray ◽  
Intermediate States ◽  
Source State ◽  
Nuclear Burning ◽  
Low Mass ◽  
X Ray Binaries ◽  
Stable Burning

ABSTRACT We detect millihertz quasi-periodic oscillations (mHz QPOs) using the Rossi X-ray Time Explorer (RXTE) from the atoll neutron-star (NS) low-mass X-ray binaries 4U 1608–52 and Aql X–1. From the analysis of all RXTE observations of 4U 1608–52 and Aql X–1, we find mHz QPOs with a significance level >3σ in 49 and 47 observations, respectively. The QPO frequency is constrained between ∼4.2 and 13.4 mHz. These types of mHz QPOs have been interpreted as being the result of marginally stable nuclear burning of He on the NS surface. We also report the discovery of a downward frequency drift in three observations of 4U 1608–52, making it the third source that shows this behaviour. We only find strong evidence of frequency drift in one occasion in Aql X–1, probably because the observations were too short to measure a significant drift. Finally, the mHz QPOs are mainly detected when both sources are in the soft or intermediate states; the cases that show frequency drift only occur when the sources are in intermediate states. Our results are consistent with the phenomenology observed for the NS systems 4U 1636–53 and EXO 0748–676, suggesting that all four sources can reach the conditions for marginally stable burning of He on the NS surface. These conditions depend on the source state in the same manner in all four systems.

scholarly journals The Chemical Evolution of the Main Component of the Binary System v Sagitarrii

1998 ◽  
Vol 11 (1) ◽  
pp. 390-390
Author(s):  
V. Leushin ◽  
V. Chuvenkov ◽  
L. Snezhko
Keyword(s):  
Chemical Composition ◽  
Binary System ◽  
Core Mass ◽  
Hydrogen Burning ◽  
Convective Mixing ◽  
Mixing Parameters ◽  
Burning Zone ◽  
Nuclear Burning ◽  
Nitrogen Abundance ◽  
Main Component

A model of internal structure and evolution of the peculiar binary system v Sgr is presented. The model corresponds well to the observed chemical composition of the main component atmosphere (10-4 H, 0.844 He, 0.013 C, 0.042 N by mass). It is supposed that about 5 million years ago the main component passed the stage of hydrogen nuclear burning in the shell over the helium core where the helium-carbon reactions took place. Because of convective mixing, the synthesized carbon diffusing into the hydrogen burning zone was catalyzing the reactions of the CN - cycle. This has resulted in anomalies in the chemical composition, particularly high nitrogen abundance in the layer observed now as the atmosphere of the main component since external layers were thrown off during the evolution. Following the calculated results, the quantitative restrictions of temperature and density in the layers and values of mixing parameters are obtained. It is shown that the best agreement with observations exists if the mass of the matter penetrating from the zone of helium-carbon reactions into the helium layer is 0.25 of the helium-carbon core mass. Moreover, the ratio of mass concentration He/C in this matter should equal 2, and the mass share diffusing into the layer of hydrogen burning should be in the range 0.25 - 0.30 of the layer mass.

scholarly journals Nuclear burning in collapsar accretion discs

2020 ◽  
Vol 499 (3) ◽  
pp. 4097-4113 ◽  
Author(s):  
Yossef Zenati ◽  
Daniel M Siegel ◽  
Brian D Metzger ◽  
Hagai B Perets
Keyword(s):  
Angular Momentum ◽  
Gamma Ray ◽  
Nuclear Reactions ◽  
Reaction Network ◽  
Accretion Discs ◽  
Late Time ◽  
Rotating Stars ◽  
Stellar Envelope ◽  
Nuclear Burning ◽  
R Process

ABSTRACT The core collapse of massive, rapidly-rotating stars are thought to be the progenitors of long-duration gamma-ray bursts (GRB) and their associated hyperenergetic supernovae (SNe). At early times after the collapse, relatively low angular momentum material from the infalling stellar envelope will circularize into an accretion disc located just outside the black hole horizon, resulting in high accretion rates necessary to power a GRB jet. Temperatures in the disc mid-plane at these small radii are sufficiently high to dissociate nuclei, while outflows from the disc can be neutron-rich and may synthesize r-process nuclei. However, at later times, and for high progenitor angular momentum, the outer layers of the stellar envelope can circularize at larger radii ≳ 107 cm, where nuclear reactions can take place in the disc mid-plane (e.g. 4He + 16O → 20Ne + γ). Here we explore the effects of nuclear burning on collapsar accretion discs and their outflows by means of hydrodynamical α-viscosity torus simulations coupled to a 19-isotope nuclear reaction network, which are designed to mimic the late infall epochs in collapsar evolution when the viscous time of the torus has become comparable to the envelope fall-back time. Our results address several key questions, such as the conditions for quiescent burning and accretion versus detonation and the generation of 56Ni in disc outflows, which we show could contribute significantly to powering GRB SNe. Being located in the slowest, innermost layers of the ejecta, the latter could provide the radioactive heating source necessary to make the spectral signatures of r-process elements visible in late-time GRB-SNe spectra.

scholarly journals The physical basis of the fission wave reactor

2008 ◽  
Vol 23 (2) ◽  
pp. 3-15 ◽  
Author(s):  
Volodymyr Pavlovych ◽  
Volodymyr Khotyayintsev ◽  
Olena Khotyayintseva
Keyword(s):  
Diffusion Equation ◽  
Main Idea ◽  
Stationary Wave ◽  
Short Review ◽  
Nuclear Fission ◽  
Stationary Processes ◽  
Wave Parameters ◽  
Nuclear Burning ◽  
Fission Wave

The main idea of slow nuclear fission wave reactor is discussed and short review of the existing works is also presented. The aim of this paper is to clarify the physics of processes, which define the stationary wave of nuclear burning, and to develop the approaches determining the wave parameters. It is shown that the diffusion equation for fluence can be used to describe the stationary and non-stationary processes in the nuclear fission wave. Two conditions of stationary wave existence are first formulated in the paper. The rule of determination of wave velocity as the eigenvalue of boundary problem is also formulated.

Nuclear Burning Stars

2008 ◽  
pp. 97-131
Author(s):  
J. H. M. M. Schmitt ◽  
B. Stelzer
Keyword(s):  
Nuclear Burning

scholarly journals The effect of diffusive nuclear burning in neutron star envelopes on cooling in accreting systems

2020 ◽  
Vol 493 (4) ◽  
pp. 4936-4944
Author(s):  
M J P Wijngaarden ◽  
Wynn C G Ho ◽  
Philip Chang ◽  
Dany Page ◽  
Rudy Wijnands ◽  
...  
Keyword(s):  
Neutron Star ◽  
Thermal Evolution ◽  
Theoretical Models ◽  
Light Elements ◽  
Heating Source ◽  
Total Luminosity ◽  
Deep Interior ◽  
Nuclear Burning ◽  
Short Time ◽  
Over Time

ABSTRACT Valuable information about the neutron star (NS) interior can be obtained by comparing observations of thermal radiation from a cooling NS crust with theoretical models. Nuclear burning of lighter elements that diffuse to deeper layers of the envelope can alter the relation between surface and interior temperatures and can change the chemical composition over time. We calculate new temperature relations and consider two effects of diffusive nuclear burning (DNB) for H–C envelopes. First, we consider the effect of a changing envelope composition and find that hydrogen is consumed on short time-scales and our temperature evolution simulations correspond to those of a hydrogen-poor envelope within ∼100 d. The transition from a hydrogen-rich to a hydrogen-poor envelope is potentially observable in accreting NS systems as an additional initial decline in surface temperature at early times after the outburst. Second, we find that DNB can produce a non-negligible heat flux, such that the total luminosity can be dominated by DNB in the envelope rather than heat from the deep interior. However, without continual accretion, heating by DNB in H–C envelopes is only relevant for <1–80 d after the end of an accretion outburst, as the amount of light elements is rapidly depleted. Comparison to crust cooling data shows that DNB does not remove the need for an additional shallow heating source. We conclude that solving the time-dependent equations of the burning region in the envelope self-consistently in thermal evolution models instead of using static temperature relations would be valuable in future cooling studies.

Influence of the radial neutron reflector efficiency on the power of fast nuclear-burning-wave reactor

2020 ◽  
Vol 148 ◽  
pp. 107699
Author(s):  
S.P. Fomin ◽  
A.I. Kirdin ◽  
M.S. Malovytsia ◽  
V.V. Pilipenko ◽  
N.F. Shul’ga
Keyword(s):  
Burning Wave ◽  
Nuclear Burning
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