Proton-rich nuclei are synthesized via photodisintegration and reverse reactions.To examine this mechanism and reproduce the observed p-nucleus abundances,it is crucial to know the reaction rates and thereby the react...Proton-rich nuclei are synthesized via photodisintegration and reverse reactions.To examine this mechanism and reproduce the observed p-nucleus abundances,it is crucial to know the reaction rates and thereby the reaction cross sections of many isotopes.Given that the number of experiments on the reactions in astrophysical energy regions is very rare,the reaction cross sections are determined by theoretical methods whose accuracy should be tested.In this study,given that ^(121)Sb is a stable seed isotope located in the region of medium-mass p-nuclei,we investigated the cross sections and reaction rates of the ^(121)Sb(α,γ)^(125)I reaction using the TALYS computer code with 432 different combinations of input parameters(OMP,LDM,and SFM).The optimal model combinations were determined using the threshold logic unit method.The theoretical reaction cross-sectional results were compared with the experimental results reported in the literature.The reaction rates were determined using the two input parameter sets most compatible with the measurements,and they were compared with the reaction rate databases:STARLIB and REACLIB.展开更多
The TMT Detailed Science Case describes the transformational science that the Thirty Meter Telescope will enable. Planned to begin science operations in 2024, TMT will open up opportunities for revolutionary discoveri...The TMT Detailed Science Case describes the transformational science that the Thirty Meter Telescope will enable. Planned to begin science operations in 2024, TMT will open up opportunities for revolutionary discoveries in essen- tially every field of astronomy, astrophysics and cosmology, seeing much fainter objects much more clearly than existing telescopes. Per this capability, TMT's sci- ence agenda fills all of space and time, from nearby comets and asteroids, to exo- planets, to the most distant galaxies, and all the way back to the very first sources of light in the universe. More than 150 astronomers from within the TMT partner- ship and beyond offered input in compiling the new 2015 Detailed Science Case. The contributing astronomers represent the entire TMT partnership, including the California Institute of Technology (Caltech), the Indian Institute of Astrophysics (HA), the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), the National Astronomical Observatory of Japan (NAOJ), the University of California, the Association of Canadian Universities for Research in Astronomy (ACURA) and US associate partner, the Association of Universities for Research in Astronomy (AURA).展开更多
A component (s-factor) with obvious promoting effect on hydrogen evolution of hydrogenase has beenisolated and extracted from a Cell=free preparation of Spirulina platensis.The effect of the s-factor in the re-actio...A component (s-factor) with obvious promoting effect on hydrogen evolution of hydrogenase has beenisolated and extracted from a Cell=free preparation of Spirulina platensis.The effect of the s-factor in the re-action system is similar to that of Na<sub>2</sub>S<sub>2</sub>O<sub>4</sub>, but is coupled with ligh. The s-factor has the maximumabsorption peak at 620 nm in the oxidized state, at 590 nm in the reduced state. The partially purifieds-factor showed two bands by SDS-PAGE and is distinctly different from phycocyanin,which has nochange of oxidized state and reduced state absorption spectra, and also has no promoting effect onhydrogenase of Spirulina platensis under the light.展开更多
A new empirical formula for the astrophysical S-factor has been suggested as a function of the Coulomb interaction parameter,center of mass energy,and barrier height.About 22 fusion reactions with ^(40,48)Ca as projec...A new empirical formula for the astrophysical S-factor has been suggested as a function of the Coulomb interaction parameter,center of mass energy,and barrier height.About 22 fusion reactions with ^(40,48)Ca as projectiles were considered for different targets,leading to compound nuclei with atomic and mass numbers varying between 40≤Z≤≤Z≤112 and 88≤A≤27888≤A≤278,respectively.The fusion cross-sections have been estimated using the geometric factor,the Gamow-Sommerfield factor,and the empirical formula for the S-factor.This study's findings showed better agreement with those of available experiments when compared to Wong's formula.The present work leads to a smaller standard deviation value than Wong's formula when used to correlate the experimental data of calcium-induced fusion reactions.Wong's formula provides a good approximation of fusion cross-sections when the center of mass energy is below the fusion barrier when compared to above the fusion barrier.展开更多
The CNO cycle is the main source of energy in stars more massive than our Sun.This process defines the energy production,the duration of which can be used to determine the lifetime of massive stars.The cycle is an imp...The CNO cycle is the main source of energy in stars more massive than our Sun.This process defines the energy production,the duration of which can be used to determine the lifetime of massive stars.The cycle is an important tool for determining the age of globular clusters.Radiative proton capture via p+^(14)N→^(15)O+γ,at energies of astrophysical interest,is an important process in the CNO cycle.In this project,we apply a potential model to describe both non-resonant and resonant reactions in the channels where radiative capture occurs through electric E1 transitions.We employed the R-matrix method to describe the ongoing reactions via M1 resonant transitions,when it was not possible to correctly reproduce the experimental data using the potential model.The partial components of the astrophysical S-factor are calculated for all possible electric and magnetic dipole transitions in ^(15)O.The linear extrapolated S-factor at zero energy(S(0))agrees well with earlier reported values for all transition types considered in this work.Based on the value of the total astrophysical S-factor,depending on the collision energy,we calculate the nuclear reaction rates for p+^(14)N→^(15)O+γ.The computed rates agree well with the results reported in the NACRE II Collaboration and most recent existing measurements.展开更多
The astrophysical S-factor of the 4He+12C radiative capture is calculated in the potential model at the energy range 0.1-2.0 MeV. Radiative capture 12C(α,γ) 16O is extremely relevant for the fate of massive stars...The astrophysical S-factor of the 4He+12C radiative capture is calculated in the potential model at the energy range 0.1-2.0 MeV. Radiative capture 12C(α,γ) 16O is extremely relevant for the fate of massive stars and determines if the remnant of a supernova explosion becomes a black hole or a neutron star. Because this reaction occurs at low energies, the experimental measurements are very difficult and perhaps impossible. In this paper, radiative capture of the 12C(α,γ) 16O reaction at very low energies is taken as a case study. In comparison with other theoretical methods and available experimental data, good agreement is achieved for the astrophysical S-factor of this process.展开更多
We summarize the recent effective field theory (EFT) studies of low-energy electroweak reactions of astrophysical interest, relevant to big-bang nucleosynthesis. The zero energy astrophysical S(0) factor for the t...We summarize the recent effective field theory (EFT) studies of low-energy electroweak reactions of astrophysical interest, relevant to big-bang nucleosynthesis. The zero energy astrophysical S(0) factor for the thermal proton radiative capture by deuteron is calculated with pionless EFT. The astrophysical S(0) factor is accurately determined to be S(0)=0.243 eV·b up to the leading order (LO). At zero energies, magnetic transition M1 gives the dominant contribution. The M1 amplitude is calculated up to the LO. A good, quantitative agreement between theoretical and experimental results is found for all observables. The demonstrations of cutoff independent calculation have also been presented.展开更多
The thick-target yield of the ^(9)Be(d,α0)7Li and ^(9)Be(d,α1)7Li*reactions has been first directly measured over deuteron energies from 66 to 94 keV.The obtained S(Ei)ofα0 andα1 have similar trends calculated by ...The thick-target yield of the ^(9)Be(d,α0)7Li and ^(9)Be(d,α1)7Li*reactions has been first directly measured over deuteron energies from 66 to 94 keV.The obtained S(Ei)ofα0 andα1 have similar trends calculated by the thin-target yield,consistent with Yan’s report within the errors.Furthermore,the parametric expression of S(E)was obtained to calculate the theoretical thick target yield,and it roughly agrees with the experimental thick target yield.展开更多
The 12C+12C fusion reaction plays a crucial role in stellar evolution and explosions.Its main open reaction channels includeα,p,n,and 8Be.Despite more than a half century of efforts,large differences remain among the...The 12C+12C fusion reaction plays a crucial role in stellar evolution and explosions.Its main open reaction channels includeα,p,n,and 8Be.Despite more than a half century of efforts,large differences remain among the experimental data of this reaction measured using various techniques.In this work,we analyze the existing data using a statistical model.Our calculation shows the following:1)the relative systematic uncertainties of the predicted branching ratios decrease as the predicted ratios increase;2)the total modified astrophysical S-factors(S^* factors)of the p andαchannels can be obtained by summing the S^* factors of their corresponding ground-state transitions and the characteristicγrays,while taking into account the contributions of the missing channels to the latter.After applying corrections based on branching ratios predicted by the statistical model,an agreement is achieved among the different data sets at Ecm>4 MeV,while some discrepancies remain at lower energies,suggesting the need for better measurements in the near future.We find that the S^* factor recently obtained from an indirect measurement is inconsistent with the direct measurement value at energies below 2.6 MeV.We recommend upper and lower limits for the 12C+12C S^* factor based on the existing models.A new 12C+12C reaction rate is also recommended.展开更多
Controversies exist among experiments and theories on the S^(*)factor of the astrophysical important reaction ^(12)C+^(12)C for energies below 3 MeV.Only frequentist approaches have been used so far for data analysis,...Controversies exist among experiments and theories on the S^(*)factor of the astrophysical important reaction ^(12)C+^(12)C for energies below 3 MeV.Only frequentist approaches have been used so far for data analysis,and the confidence levels or theoretical errors are not available from previous theoretical predictions.In this study,the Bayesian method is employed to provide theoretical predictions and its 1σconfidence level based on all the currently available experimental data for the first time.The improved coupled-channels model CCFULL-FEM implemented with the finite element method as well as the Markov chain Monte Carlo approach emcee are adopted to analyze the non-resonant behavior of this reaction.The posterior distribution of the Woods-Saxon potential parameters is investigated.Compared with the widely used frequentist method MIGRAD within the Minuit minimization program,the Bayesian method has a significant advantage for exploring the potential parameter space.When the existing experimental data measured down to subbarrier energies are considered,the potential parameters are constrained to a very narrow range,and the predictions of the S^(*) factor showed no sharp decrease in the low-energy region.展开更多
Radiative capture p+^(9)Be→^(10)B+γ at energies bearing astrophysical importance is a key process for the spectroscopic study of ^(10)B.In this work,we consider the radiative capture cross-section for the ^(9)Be(p,...Radiative capture p+^(9)Be→^(10)B+γ at energies bearing astrophysical importance is a key process for the spectroscopic study of ^(10)B.In this work,we consider the radiative capture cross-section for the ^(9)Be(p,γ)^(10)B within the framework of the potential model and the R-matrix method for the multi-entrance channel cases.In certain cases,when the potential fails,therefore,the R-matrix approach is better to use for the description of partial components of the cross-section that have sharp or broad resonances.For all possible electric and magnetic dipole transitions,partial components of the astrophysical S-factor are computed.The computed value of the total S-factor at zero energy is consistent with the reported results.展开更多
文摘Proton-rich nuclei are synthesized via photodisintegration and reverse reactions.To examine this mechanism and reproduce the observed p-nucleus abundances,it is crucial to know the reaction rates and thereby the reaction cross sections of many isotopes.Given that the number of experiments on the reactions in astrophysical energy regions is very rare,the reaction cross sections are determined by theoretical methods whose accuracy should be tested.In this study,given that ^(121)Sb is a stable seed isotope located in the region of medium-mass p-nuclei,we investigated the cross sections and reaction rates of the ^(121)Sb(α,γ)^(125)I reaction using the TALYS computer code with 432 different combinations of input parameters(OMP,LDM,and SFM).The optimal model combinations were determined using the threshold logic unit method.The theoretical reaction cross-sectional results were compared with the experimental results reported in the literature.The reaction rates were determined using the two input parameter sets most compatible with the measurements,and they were compared with the reaction rate databases:STARLIB and REACLIB.
文摘The TMT Detailed Science Case describes the transformational science that the Thirty Meter Telescope will enable. Planned to begin science operations in 2024, TMT will open up opportunities for revolutionary discoveries in essen- tially every field of astronomy, astrophysics and cosmology, seeing much fainter objects much more clearly than existing telescopes. Per this capability, TMT's sci- ence agenda fills all of space and time, from nearby comets and asteroids, to exo- planets, to the most distant galaxies, and all the way back to the very first sources of light in the universe. More than 150 astronomers from within the TMT partner- ship and beyond offered input in compiling the new 2015 Detailed Science Case. The contributing astronomers represent the entire TMT partnership, including the California Institute of Technology (Caltech), the Indian Institute of Astrophysics (HA), the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), the National Astronomical Observatory of Japan (NAOJ), the University of California, the Association of Canadian Universities for Research in Astronomy (ACURA) and US associate partner, the Association of Universities for Research in Astronomy (AURA).
文摘A component (s-factor) with obvious promoting effect on hydrogen evolution of hydrogenase has beenisolated and extracted from a Cell=free preparation of Spirulina platensis.The effect of the s-factor in the re-action system is similar to that of Na<sub>2</sub>S<sub>2</sub>O<sub>4</sub>, but is coupled with ligh. The s-factor has the maximumabsorption peak at 620 nm in the oxidized state, at 590 nm in the reduced state. The partially purifieds-factor showed two bands by SDS-PAGE and is distinctly different from phycocyanin,which has nochange of oxidized state and reduced state absorption spectra, and also has no promoting effect onhydrogenase of Spirulina platensis under the light.
文摘A new empirical formula for the astrophysical S-factor has been suggested as a function of the Coulomb interaction parameter,center of mass energy,and barrier height.About 22 fusion reactions with ^(40,48)Ca as projectiles were considered for different targets,leading to compound nuclei with atomic and mass numbers varying between 40≤Z≤≤Z≤112 and 88≤A≤27888≤A≤278,respectively.The fusion cross-sections have been estimated using the geometric factor,the Gamow-Sommerfield factor,and the empirical formula for the S-factor.This study's findings showed better agreement with those of available experiments when compared to Wong's formula.The present work leads to a smaller standard deviation value than Wong's formula when used to correlate the experimental data of calcium-induced fusion reactions.Wong's formula provides a good approximation of fusion cross-sections when the center of mass energy is below the fusion barrier when compared to above the fusion barrier.
文摘The CNO cycle is the main source of energy in stars more massive than our Sun.This process defines the energy production,the duration of which can be used to determine the lifetime of massive stars.The cycle is an important tool for determining the age of globular clusters.Radiative proton capture via p+^(14)N→^(15)O+γ,at energies of astrophysical interest,is an important process in the CNO cycle.In this project,we apply a potential model to describe both non-resonant and resonant reactions in the channels where radiative capture occurs through electric E1 transitions.We employed the R-matrix method to describe the ongoing reactions via M1 resonant transitions,when it was not possible to correctly reproduce the experimental data using the potential model.The partial components of the astrophysical S-factor are calculated for all possible electric and magnetic dipole transitions in ^(15)O.The linear extrapolated S-factor at zero energy(S(0))agrees well with earlier reported values for all transition types considered in this work.Based on the value of the total astrophysical S-factor,depending on the collision energy,we calculate the nuclear reaction rates for p+^(14)N→^(15)O+γ.The computed rates agree well with the results reported in the NACRE II Collaboration and most recent existing measurements.
文摘The astrophysical S-factor of the 4He+12C radiative capture is calculated in the potential model at the energy range 0.1-2.0 MeV. Radiative capture 12C(α,γ) 16O is extremely relevant for the fate of massive stars and determines if the remnant of a supernova explosion becomes a black hole or a neutron star. Because this reaction occurs at low energies, the experimental measurements are very difficult and perhaps impossible. In this paper, radiative capture of the 12C(α,γ) 16O reaction at very low energies is taken as a case study. In comparison with other theoretical methods and available experimental data, good agreement is achieved for the astrophysical S-factor of this process.
文摘We summarize the recent effective field theory (EFT) studies of low-energy electroweak reactions of astrophysical interest, relevant to big-bang nucleosynthesis. The zero energy astrophysical S(0) factor for the thermal proton radiative capture by deuteron is calculated with pionless EFT. The astrophysical S(0) factor is accurately determined to be S(0)=0.243 eV·b up to the leading order (LO). At zero energies, magnetic transition M1 gives the dominant contribution. The M1 amplitude is calculated up to the LO. A good, quantitative agreement between theoretical and experimental results is found for all observables. The demonstrations of cutoff independent calculation have also been presented.
基金Partly supported by National Natural Science Foundation of China(11305080)The Fundamental Research Funds for the Central Universities(lzujbky-2019-53)。
文摘The thick-target yield of the ^(9)Be(d,α0)7Li and ^(9)Be(d,α1)7Li*reactions has been first directly measured over deuteron energies from 66 to 94 keV.The obtained S(Ei)ofα0 andα1 have similar trends calculated by the thin-target yield,consistent with Yan’s report within the errors.Furthermore,the parametric expression of S(E)was obtained to calculate the theoretical thick target yield,and it roughly agrees with the experimental thick target yield.
基金Supported by the National Key Research and Development Program of China(2016YFA0400501)National Natural Science Foundation of China(11805291,11575292,11475228,11490564,11875329)+5 种基金the U.S.Department of Energy(DE-AC07-05ID14517)Fundamental Research Funds for the Central Universities(18lgpy84)Continuous Basic Scientific Research Project(WDJC-2019-13)CNNC R&D program(FA18000201)the support of the Strategic Priority Research Program of Chinese Academy of Sciences(XDB34000000)the“Hundred Talents Program”of the Chinese Academy of Sciences。
文摘The 12C+12C fusion reaction plays a crucial role in stellar evolution and explosions.Its main open reaction channels includeα,p,n,and 8Be.Despite more than a half century of efforts,large differences remain among the experimental data of this reaction measured using various techniques.In this work,we analyze the existing data using a statistical model.Our calculation shows the following:1)the relative systematic uncertainties of the predicted branching ratios decrease as the predicted ratios increase;2)the total modified astrophysical S-factors(S^* factors)of the p andαchannels can be obtained by summing the S^* factors of their corresponding ground-state transitions and the characteristicγrays,while taking into account the contributions of the missing channels to the latter.After applying corrections based on branching ratios predicted by the statistical model,an agreement is achieved among the different data sets at Ecm>4 MeV,while some discrepancies remain at lower energies,suggesting the need for better measurements in the near future.We find that the S^* factor recently obtained from an indirect measurement is inconsistent with the direct measurement value at energies below 2.6 MeV.We recommend upper and lower limits for the 12C+12C S^* factor based on the existing models.A new 12C+12C reaction rate is also recommended.
基金Supported by the National Natural Science Foundation of China(11635015,11805280,U1732145,11705285,U1867212,11961131012)the Continuous Basic Scientific Research Project(WDJC-2019-13)+1 种基金the Young Talent Development Foundation(YC212212000101)the Leading Innovation Project(LC192209000701,LC202309000201)。
文摘Controversies exist among experiments and theories on the S^(*)factor of the astrophysical important reaction ^(12)C+^(12)C for energies below 3 MeV.Only frequentist approaches have been used so far for data analysis,and the confidence levels or theoretical errors are not available from previous theoretical predictions.In this study,the Bayesian method is employed to provide theoretical predictions and its 1σconfidence level based on all the currently available experimental data for the first time.The improved coupled-channels model CCFULL-FEM implemented with the finite element method as well as the Markov chain Monte Carlo approach emcee are adopted to analyze the non-resonant behavior of this reaction.The posterior distribution of the Woods-Saxon potential parameters is investigated.Compared with the widely used frequentist method MIGRAD within the Minuit minimization program,the Bayesian method has a significant advantage for exploring the potential parameter space.When the existing experimental data measured down to subbarrier energies are considered,the potential parameters are constrained to a very narrow range,and the predictions of the S^(*) factor showed no sharp decrease in the low-energy region.
文摘Radiative capture p+^(9)Be→^(10)B+γ at energies bearing astrophysical importance is a key process for the spectroscopic study of ^(10)B.In this work,we consider the radiative capture cross-section for the ^(9)Be(p,γ)^(10)B within the framework of the potential model and the R-matrix method for the multi-entrance channel cases.In certain cases,when the potential fails,therefore,the R-matrix approach is better to use for the description of partial components of the cross-section that have sharp or broad resonances.For all possible electric and magnetic dipole transitions,partial components of the astrophysical S-factor are computed.The computed value of the total S-factor at zero energy is consistent with the reported results.