Rapid neutron capture process in supernovae and chemical element formation

Baruah, Rulee; Duorah, K.; Duorah, H. L.

doi:10.1007/s12036-009-0013-x

Cited by 4 publications

(4 citation statements)

References 18 publications

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“…Recently, it has been shown, on the other hand, that 164 Er, 152 Gd and 180 Ta may have large s-process contributions, nevertheless, and that the ν-process may contribute to 138 La and 180 Ta (see, e.g., [3] and references therein). The remaining p nuclei are thought to be produced in the γ-process which includes combination of (γ,n), (γ,p) and (γ,α) reactions [1][2][3][4][5][6][7][8][9].…”

Section: Introductionmentioning

confidence: 99%

Test of statistical model cross section calculations forα-induced reactions onAg107at energies of astrophysical interest

et al. 2015

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Background: Astrophysical reaction rates, which are mostly derived from theoretical cross sections, are necessary input to nuclear reaction network simulations for studying the origin of p nuclei. Past experiments have found a considerable difference between theoretical and experimental cross sections in some cases, especially for (α,γ) reactions at low energy. Therefore, it is important to experimentally test theoretical cross section predictions at low, astrophysically relevant energies.Purpose: The aim is to measure reaction cross sections of 107 Ag(α,γ) 111 In and 107 Ag(α,n) 110 In at low energies in order to extend the experimental database for astrophysical reactions involving α particles towards lower mass numbers. Reaction rate predictions are very sensitive to the optical model parameters and this introduces a large uncertainty into theoretical rates involving α particles at low energy. We have also used Hauser-Feshbach statistical model calculations to study the origin of possible discrepancies between prediction and data.Method: An activation technique has been used to measure the reaction cross sections at effective center of mass energies between 7.79 MeV and 12.50 MeV. Isomeric and ground state cross sections of the (α,n) reaction were determined separately. Results:The measured cross sections were found to be lower than theoretical predictions for the (α,γ) reaction. Varying the calculated averaged widths in the Hauser-Feshbach model, it became evident that the data for the (α,γ) and (α,n) reactions can only be simultaneously reproduced when rescaling the ratio of γ-to neutron width and using an energy-dependent imaginary part in the optical α+ 107 Ag potential. Conclusions:The new data extend the range of measured charged-particle cross sections for astrophysical applications to lower mass numbers and lower energies. The modifications in the model predictions required to reproduce the present data are fully consistent with what was found in previous investigations. Thus, our results confirm the previously suggested energy-dependent modification of the optical α+nucleus potential.

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Section: Introductionmentioning

confidence: 99%

Test of statistical model cross section calculations forα-induced reactions onAg107at energies of astrophysical interest

et al. 2015

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“…The Hartree-Fock calculation including forbidden transitions with Skyrme interaction and pairing correlations can also well reproduce measured half-lives of neutron-rich nuclei with A ≈ 190 [30]. In other studies [10,[31][32][33], it was found that the determination of the neutron density and temperature conditions for the (γ, n) − (n, γ) equilibrium establishment or WP approximation strongly depends on neutron and/or two-neutron separation energies of neutron-rich nuclei. In particular, the deviations in two-neutron separation energies of 78 Ni and 84 Zn due to the differences among the RMF [34], FRDM [35], and WS [36,37] mass models lead to a large change, from 10 23 to 10 26 cm −3 at 1 GigaKelvin (GK), in the neutron density required by the N = 50 WP [33].…”

Section: Introductionmentioning

confidence: 60%

Examination of n − T ₉ conditions required by N = 50, 82, 126 waiting points in r-process

Ly¹,

Duy²,

Uyen³

et al. 2021

Commun. Theor. Phys.

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We examined the conditions of neutron density (n) and temperature (T 9 ) required for the N = 50, 82, and 126 isotopes to be waiting points (WP) in the r-process. The nuclear mass based on experimental data presented in the AME2020 database (AME and AME ± Δ) and that predicted using FRDM, WS4, DZ10, and KTUY models were employed in our estimations. We found that the conditions required by the N = 50 WP significantly overlap with those required by the N = 82 ones, except for the WS4 model. In addition, the upper (or lower) bounds of the n − T 9 conditions based on the models are different from each other due to the deviations in the two-neutron separation energies. The standard deviations in the nuclear mass of 108 isotopes in the three N = 50, 82, and 126 groups are about rms = 0.192 and 0.434 MeV for the pairs of KTUY-AME and WS4-KTUY models, respectively. We found that these mass uncertainties result in a large discrepancy in the n n − T 9 conditions, leading to significant differences in the conditions for simultaneously appearing all the three peaks in the r-process abundance. The newly updated FRDM and WS4 calculations can give the overall conditions for the appearance of all the peaks but vice versa for their old versions in a previous study. The change in the final r-process isotopic abundance due to the mass uncertainty is from a few factors to three orders of magnitude. Therefore, accurate nuclear masses of the r-process key nuclei, especially for 76 Fe, 81 Cu, 127 Rh, 132 Cd, 192 Dy, and 197 Tm, are highly recommended to be measured in radioactive-ion beam facilities for a better understanding of the r-process evolution.

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“…The produced very neutron rich progenitor nuclei then undergo a series of β − -decays until they reach a stable nucleus whose calculated abundance can then be compared with observation. The r-process path and the elements obtained in these astrophysical conditions are presented in an earlier paper by Baruah et al (2009). It was recognised that the extremely high neutron densities and temperatures needed were probably attainable only in dynamical events, i.e.…”

Section: Introductionmentioning

confidence: 92%

Isotopic r-process abundances produced by supernova explosions

Baruah

Duorah

2012

Astrophys Space Sci

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The rapid neutron capture process (r-process) is one of the major nucleosynthesis processes responsible for the synthesis of heavy nuclei beyond iron. Isotopes beyond Fe are most exclusively formed in neutron capture processes and more heavier ones are produced by the r-process. Approximately half of the heavy elements with mass number A > 70 and all of the actinides in the solar system are believed to have been produced in the r-process. We have studied the r-process in supernovae for production of heavy elements beyond A = 40 with the newest mass values available. The supernovae envelopes at a temperature >10 9 K and neutron density of 10 24 cm −3 are considered to be one of the most potential sites for the r-process. We investigate the r-process in a site-independent, classical approach which assumes a chemical equilibrium between neutron captures and photodisintegrations followed by a β-flow equilibrium. We have studied the r-process path corresponding to temperatures ranging from 1.0 × 10 9 K to 3.0 × 10 9 K and neutron density ranging from 10 20 cm −3 to 10 30 cm −3 . The primary goal of the r-process calculations is to fit the global abundance curve for solar system r-process isotopes by varying time dependent parameters such as temperature and neutron density. This method aims at comparing the calculated abundances of the stable isotopes with observation. The abundances obtained are compared with supernova explosion condition and found in good agreement. The elements ob-R. Baruah ( ) tained along the r-process path are compared with the observed data at all the above temperature and density range.

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Rapid neutron capture process in supernovae and chemical element formation

Cited by 4 publications

References 18 publications

Test of statistical model cross section calculations forα-induced reactions onAg107at energies of astrophysical interest

Test of statistical model cross section calculations forα-induced reactions onAg107at energies of astrophysical interest

Examination of n − T ₉ conditions required by N = 50, 82, 126 waiting points in r-process

Isotopic r-process abundances produced by supernova explosions

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Rapid neutron capture process in supernovae and chemical element formation

Cited by 4 publications

References 18 publications

Test of statistical model cross section calculations forα-induced reactions onAg107at energies of astrophysical interest

Test of statistical model cross section calculations forα-induced reactions onAg107at energies of astrophysical interest

Examination of n − T 9 conditions required by N = 50, 82, 126 waiting points in r-process

Isotopic r-process abundances produced by supernova explosions

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Examination of n − T ₉ conditions required by N = 50, 82, 126 waiting points in r-process