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.

scholarly journals The Relevance of Nuclear Reactions for Standard Solar Models Construction

2021 ◽  
Vol 7 ◽  
Author(s):  
Francesco L. Villante ◽  
Aldo Serenelli
Keyword(s):  
Nuclear Reaction ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Direct Detection ◽  
Reaction Rates ◽  
Precise Determination ◽  
Reaction Cross ◽  
Solar Interior ◽  
Current Status ◽  
The Sun

The fundamental processes by which nuclear energy is generated in the Sun have been known for many years. However, continuous progress in areas such as neutrino experiments, stellar spectroscopy and helioseismic data and techniques requires ever more accurate and precise determination of nuclear reaction cross sections, a fundamental physical input for solar models. In this work, we review the current status of (standard) solar models and present a complete discussion on the relevance of nuclear reactions for detailed predictions of solar properties. In addition, we also provide an analytical model that helps understanding the relation between nuclear cross sections, neutrino fluxes and the possibility they offer for determining physical characteristics of the solar interior. The latter is of particular relevance in the context of the conundrum posed by the solar composition, the solar abundance problem, and in the light of the first ever direct detection of solar CN neutrinos recently obtained by the Borexino collaboration. Finally, we present a short list of wishes about the precision with which nuclear reaction rates should be determined to allow for further progress in our understanding of the Sun.

scholarly journals The feasibility of measuring the nuclear reaction cross sections at energies of several KeV in a target under laser compression

1987 ◽  
Vol 5 (2) ◽  
pp. 399-404 ◽  
Author(s):  
V. I. Kukulin ◽  
V. M. Krasnopol'sky ◽  
V. T. Voronchev
Keyword(s):  
Nuclear Reaction ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Velocity Distribution Function ◽  
Reaction Cross ◽  
Straightforward Method ◽  
Energy Behaviour ◽  
Low Energies ◽  
Ion Velocity Distribution Function ◽  
Reaction Cross Sections

The work proposes a straightforward method for determining the nuclear reaction cross sections at extremely low energies (E ≃ 1–100 keV) on the basis of the measurements of the relative yield of fast particles which are products of the nuclear reactions in a target under laser compression. On the other hand, the proposed method makes it possible to find the averaged form of the ion velocity distribution function if the low-energy behaviour of the respective cross sections is known.

scholarly journals On the Statistical Theory of Nuclear Reactions

1978 ◽  
Vol 31 (2) ◽  
pp. 151 ◽  
Author(s):  
WK Bertram
Keyword(s):  
Statistical Theory ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Reaction Cross ◽  
Open Channels ◽  
S Matrix ◽  
Reaction Cross Sections

The statistical theory of energy-averaged reaction cross sections is examined using the pole expansion of the S-matrix. Exact expressions for the average cross sections in terms of the parameters of the S-matrix are derived for the case when there are two open channels. It is shown that when the number of channels exceeds two, the average cross sections can be evaluated provided the poles of the S-matrix are evenly spaced.

Study of level density and reaction cross-sections in Thorium isotopes

2019 ◽  
Vol 34 (12) ◽  
pp. 1950091
Author(s):  
Erumban Ummukulsu ◽  
Nithu Ashok ◽  
Antony Joseph
Keyword(s):  
Cross Sections ◽  
Nuclear Reactions ◽  
Level Density ◽  
Reaction Cross ◽  
Drip Line ◽  
Density Parameter ◽  
Nuclear Level Density ◽  
Talys 1.6 ◽  
Experimental Values ◽  
Thorium Isotopes

A theoretical study of nuclear level density of Thorium nuclei that exist on and off the beta-stability line is carried out using Talys 1.6. The level density parameter a and spin cut-off factor [Formula: see text] for Thorium isotopes [Formula: see text]Th are estimated. The values of both these parameters decrease towards the neutron drip line and the proton drip line. Cross-sections for [Formula: see text] and [Formula: see text] reactions for Thorium isotopes are also calculated. The estimated and experimental values of cross-sections for [Formula: see text]Th are comparable. These evaluated data are useful in understanding the mechanism of nuclear reactions taking place under extreme conditions including those in nucleosynthesis.

scholarly journals Thermonuclear Reaction Rates for Reactions Leading to N = 28 Nuclei

1995 ◽  
Vol 48 (1) ◽  
pp. 125
Author(s):  
A.J Morton ◽  
DG Sargood
Keyword(s):  
Statistical Model ◽  
Nuclear Reaction ◽  
Cross Sections ◽  
Optical Model ◽  
Reaction Rates ◽  
Reaction Cross ◽  
Model Parameters ◽  
Thermonuclear Reaction ◽  
Model Calculations ◽  
Reaction Cross Sections

Nuclear reaction cross sections derived from statistical-model calculations have been used in the calculation of thermonuclear reaction rates for 36 nuclei at temperatures that are representative of the interiors of evolving stars and supernovae as nucleosynthesis approaches the production of nuclei with N = 28. The statistical-model calculations used optical-model parameters in the particle channels which had been selected to give the best overall agreement between theoretical and experimental cross sections for reactions on stable target nuclei in the mass and energy ranges of importance for the stellar conditions of interest. The optical-model parameters used, and the stellar reaction rates obtained, are tabulated. Comparisons are made between these stellar rates and those from other statistical-model calculations in the literature.

scholarly journals Electron Screening in Nuclear Astrophysics

2020 ◽  
Vol 227 ◽  
pp. 01012
Author(s):  
Matej Lipoglavsek ◽  
Aleksandra Cvetinović
Keyword(s):  
Nuclear Reaction ◽  
Cross Sections ◽  
Inverse Kinematics ◽  
Nuclear Reactions ◽  
Nuclear Astrophysics ◽  
Reaction Cross ◽  
Electron Screening ◽  
Low Energies ◽  
Order Of Magnitude ◽  
Reaction Cross Sections

Electron screening in an important effect that cannot be neglected in nuclear astrophysics, since it influences nuclear reaction cross sections at low energies. We are trying to understand why most measurements in inverse kinematics on solid targets give electron screening potentials more than an order of magnitude above predictions. Below we report our latest results on electron screening in nuclear reactions 1H(14N,γ)15O and 2H(19F,ρ)2°F in both inverse and normal kinematics. The analysis is in progress.

scholarly journals Statistical model calculations of the 232Th(n,2n) reaction

2019 ◽  
Vol 11 ◽  
Author(s):  
D. Karamanis ◽  
S. Andriamonje ◽  
P. A. Assimakopoulos ◽  
G. Doukellis ◽  
D. A. Karademos ◽  
...  
Keyword(s):  
Experimental Data ◽  
Statistical Model ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Level Density ◽  
Computer Code ◽  
Reaction Cross ◽  
Tandem Accelerator ◽  
Model Calculations ◽  
Equilibrium Evaporation

On the context of the Cern n_TOF collaboration the 232Th(n,2n)231Th reaction cross section has been measured relative to the 56Fe(n,p)56Mn and 27Al(n,a)24Na reaction cross sections by the activation method for neutron energies up to 11 MeV. The neutrons were produced via the 2H(d,n) reaction using a deuterium filled gas-cell, at the 5.5MV TANDEM Accelerator of NCSR "Demokritos". In addition to the experimental work, theoretical Statistical model calculations have been performed using the computer code STAPRE/F. The code STAPRE is designed to calculate energy averaged cross sections for particle induced nuclear reactions with several emitted particles and gamma rays under the assumption of sequential evaporation. For the first evaporation step preequilibrium emission is taken into account while population of states resulting from the first equilibrium evaporation step is calculated using the Hauser-Feschbach theory. Fission process competition is also taken into account in the evaporation steps. Sensitive parameters for the calculation, like level density parameters, have been adopted after fitting experimental data for the competing (n,f) reaction. The results are being compared to the experimental data.

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