The open question of where, when, and how the heavy elements beyond iron enrich our Universe has triggered a new era in nuclear physics studies. Of all the relevant nuclear physics inputs, the mass of very neutron-ric...The open question of where, when, and how the heavy elements beyond iron enrich our Universe has triggered a new era in nuclear physics studies. Of all the relevant nuclear physics inputs, the mass of very neutron-rich nuclides is a key quantity for revealing the origin of heavy elements beyond iron. Although the precise determination of this property is a great challenge, enormous progress has been made in recent decades, and it has contributed significantly to both nuclear structure and astrophysical nucleosynthesis studies. In this review, we first survey our present knowledge of the nuclear mass surface, emphasizing the importance of nuclear mass precision in r-process calculations. We then discuss recent progress in various methods of nuclear mass measurement with a few selected examples. For each method, we focus on recent breakthroughs and discuss possible ways of improving the weighing of r-process nuclides.展开更多
Key nuclear inputs for the astrophysical r-process simulations are the weak interaction rates.Consequently,the accuracy of these inputs directly affects the reliability of nucleosynthesis modeling.The majority of the ...Key nuclear inputs for the astrophysical r-process simulations are the weak interaction rates.Consequently,the accuracy of these inputs directly affects the reliability of nucleosynthesis modeling.The majority of the stellar rates,used in simulation studies are calculated by invoking the Brink-Axel(BA)hypothesis.The BA hypothesis assumes that the strength functions of all parent excited states are the same as for the ground state,only shifted in energies.However,the BA hypothesis has to be tested against microscopically calculated state-by-state rates.In this project,we study the impact of the BA hypothesis on calculated stellarβ^(-)-decay and electron capture rates.Our investigation include both unique first forbidden(U1F)and allowed transitions for 106 neutron-rich trans-iron nuclei([27,77]≤[Z,A]≤[82,208]).The calculations were performed using the deformed proton-neutron quasiparticle random-phase approximation(pn-QRPA)model with a simple plus quadrupole separable and schematic interaction.Waiting-point and several key r-process nuclei lie within the considered mass region of the nuclear chart.We computed electron capture andβ^(-)-decay rates using two different prescriptions for strength functions.One was based on invoking the BA hypothesis and the other was the state-by-state calculation of strength functions,under stellar density and temperature conditions([10,1]≤[ρYe(g/cm^(3)),T(GK)]≤[10^(11),30]).Our results show that the BA hypothesis invoked U1Fβ^(-)rates are overestimated by 4–5 orders of magnitude as compared to microscopic rates.For capture rates,more than two orders of magnitude differences were noted when applying the BA hypothesis.It was concluded that the BA hypothesis is not a reliable approximation,especially forβ^(-)-decay forbidden transitions.展开更多
The rapid neutron-capture process(r-process) is one of the main mechanisms to explain the origin of heavy elements in the universe. Although the past decades have seen great progress in understanding this process, the...The rapid neutron-capture process(r-process) is one of the main mechanisms to explain the origin of heavy elements in the universe. Although the past decades have seen great progress in understanding this process, the related nuclear physics inputs to r-process models include significant uncertainty. In this study, ten nuclear mass models, including macroscopic, macroscopicmicroscopic, and microscopic models, are used to calculate the β-decay rates and neutron-capture rates of the neutron-rich isotopes for the r-process simulations occurring in three classes of astrophysical conditions. The final r-process abundances include uncertainties introduced by the nuclear mass model mainly through the variation of neutron-capture rates, whereas the uncertainties of β-decay rates make a relatively small contribution. The uncertainties in different astrophysical scenarios are also investigated,and are found to be connected to the diverse groups of nuclei produced during nucleosynthesis.展开更多
We discuss current attempts to employ the modified potential cluster model to describe the available experimental data on the^(13)B(n,γ0+1)^(14)B total cross-sections.The estimated results of the M1 and E1 transition...We discuss current attempts to employ the modified potential cluster model to describe the available experimental data on the^(13)B(n,γ0+1)^(14)B total cross-sections.The estimated results of the M1 and E1 transitions from the n^(13)B scattering states to the ground and first excited states of^(14)B are presented.The 1st resonance at Ex=1.275 MeV(1+)is revealed in both the cross-section and reaction rate.Within the variation in the asymptotic constant,a thermal cross-section interval of 5.1-8.9 mb is proposed.Based on the theoretical total cross-sections at energies of 0.01 eV to 5 MeV,we calculate the reaction rate in the temperature range of 0.01 to 10T9.The ignition T9 values of the^(13)B(n,γ0+1)^(14)B reaction depending on a neutron number density n_(n)of~10^(22)cm^(−3)are determined.The radiative neutron capture reaction rates on the boron^(10-13)B and carbon^(12-14)Сisotopes are compared.展开更多
Research activities of nuclear physics at Radioactive Isotope Beam Factory over 10 years are reviewed and future directions are also discussed. Conceptual ideas in designing the facility as well as experimental device...Research activities of nuclear physics at Radioactive Isotope Beam Factory over 10 years are reviewed and future directions are also discussed. Conceptual ideas in designing the facility as well as experimental devices are introduced. Special emphasis is given to highlighted results obtained at RIBF.展开更多
Experimental data ofβ--decay half-lives of nuclei with atomic number between 20 and 190 are investigated.A systematic formula has been proposed to calculateβ^--decay half-lives of neutron-rich nuclei,with a particul...Experimental data ofβ--decay half-lives of nuclei with atomic number between 20 and 190 are investigated.A systematic formula has been proposed to calculateβ^--decay half-lives of neutron-rich nuclei,with a particular consideration on shell and pair effects,the decay energy Q as well as the nucleon numbers(Z,N).Although the formula has relatively few parameters,it reproduces the experimentalβ^--decay half-lives of neutron-rich nuclei very well.The predicted half-lives for the r-process relevant nuclei obtained with the current formula serve as reliable input in the r-process model calculations.展开更多
We examined the conditions of neutron density(n) and temperature(T9) 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...We examined the conditions of neutron density(n) and temperature(T9) 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-T9 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 Me V for the pairs of KTUY-AME and WS4-KTUY models,respectively. We found that these mass uncertainties result in a large discrepancy in the nn-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,81Cu,127Rh,132Cd,192Dy, and 197Tm, are highly recommended to be measured in radioactive-ion beam facilities for a better understanding of the r-process evolution.展开更多
文摘The open question of where, when, and how the heavy elements beyond iron enrich our Universe has triggered a new era in nuclear physics studies. Of all the relevant nuclear physics inputs, the mass of very neutron-rich nuclides is a key quantity for revealing the origin of heavy elements beyond iron. Although the precise determination of this property is a great challenge, enormous progress has been made in recent decades, and it has contributed significantly to both nuclear structure and astrophysical nucleosynthesis studies. In this review, we first survey our present knowledge of the nuclear mass surface, emphasizing the importance of nuclear mass precision in r-process calculations. We then discuss recent progress in various methods of nuclear mass measurement with a few selected examples. For each method, we focus on recent breakthroughs and discuss possible ways of improving the weighing of r-process nuclides.
基金supported by the Higher Education Commission Pakistan through Project (0-15394/NRPU/R&D/HEC/2021)。
文摘Key nuclear inputs for the astrophysical r-process simulations are the weak interaction rates.Consequently,the accuracy of these inputs directly affects the reliability of nucleosynthesis modeling.The majority of the stellar rates,used in simulation studies are calculated by invoking the Brink-Axel(BA)hypothesis.The BA hypothesis assumes that the strength functions of all parent excited states are the same as for the ground state,only shifted in energies.However,the BA hypothesis has to be tested against microscopically calculated state-by-state rates.In this project,we study the impact of the BA hypothesis on calculated stellarβ^(-)-decay and electron capture rates.Our investigation include both unique first forbidden(U1F)and allowed transitions for 106 neutron-rich trans-iron nuclei([27,77]≤[Z,A]≤[82,208]).The calculations were performed using the deformed proton-neutron quasiparticle random-phase approximation(pn-QRPA)model with a simple plus quadrupole separable and schematic interaction.Waiting-point and several key r-process nuclei lie within the considered mass region of the nuclear chart.We computed electron capture andβ^(-)-decay rates using two different prescriptions for strength functions.One was based on invoking the BA hypothesis and the other was the state-by-state calculation of strength functions,under stellar density and temperature conditions([10,1]≤[ρYe(g/cm^(3)),T(GK)]≤[10^(11),30]).Our results show that the BA hypothesis invoked U1Fβ^(-)rates are overestimated by 4–5 orders of magnitude as compared to microscopic rates.For capture rates,more than two orders of magnitude differences were noted when applying the BA hypothesis.It was concluded that the BA hypothesis is not a reliable approximation,especially forβ^(-)-decay forbidden transitions.
基金supported by the National Natural Science Foundation of China(Grant Nos.11875070,U1832211,and 11711540016)the National Key R&D program of China(Grant No.2016YFA0400504)+1 种基金the Natural Science Foundation of Anhui Province(Grant No.1708085QA10)the Open fund for Discipline Construction,Institute of Physical Science and Information Technology,Anhui University
文摘The rapid neutron-capture process(r-process) is one of the main mechanisms to explain the origin of heavy elements in the universe. Although the past decades have seen great progress in understanding this process, the related nuclear physics inputs to r-process models include significant uncertainty. In this study, ten nuclear mass models, including macroscopic, macroscopicmicroscopic, and microscopic models, are used to calculate the β-decay rates and neutron-capture rates of the neutron-rich isotopes for the r-process simulations occurring in three classes of astrophysical conditions. The final r-process abundances include uncertainties introduced by the nuclear mass model mainly through the variation of neutron-capture rates, whereas the uncertainties of β-decay rates make a relatively small contribution. The uncertainties in different astrophysical scenarios are also investigated,and are found to be connected to the diverse groups of nuclei produced during nucleosynthesis.
基金the Ministry of Science and Higher Education of the Republic of Kazakhstan(AP09259174)。
文摘We discuss current attempts to employ the modified potential cluster model to describe the available experimental data on the^(13)B(n,γ0+1)^(14)B total cross-sections.The estimated results of the M1 and E1 transitions from the n^(13)B scattering states to the ground and first excited states of^(14)B are presented.The 1st resonance at Ex=1.275 MeV(1+)is revealed in both the cross-section and reaction rate.Within the variation in the asymptotic constant,a thermal cross-section interval of 5.1-8.9 mb is proposed.Based on the theoretical total cross-sections at energies of 0.01 eV to 5 MeV,we calculate the reaction rate in the temperature range of 0.01 to 10T9.The ignition T9 values of the^(13)B(n,γ0+1)^(14)B reaction depending on a neutron number density n_(n)of~10^(22)cm^(−3)are determined.The radiative neutron capture reaction rates on the boron^(10-13)B and carbon^(12-14)Сisotopes are compared.
文摘Research activities of nuclear physics at Radioactive Isotope Beam Factory over 10 years are reviewed and future directions are also discussed. Conceptual ideas in designing the facility as well as experimental devices are introduced. Special emphasis is given to highlighted results obtained at RIBF.
基金supported by the National Natural Science Foundation of China(Grant Nos.11490563 and 11375269)the National Basic Research Program of China(Grant No.2013CB834406)the National Key Research and Development Program of China(Grant No.2016YFA0400502)
文摘Experimental data ofβ--decay half-lives of nuclei with atomic number between 20 and 190 are investigated.A systematic formula has been proposed to calculateβ^--decay half-lives of neutron-rich nuclei,with a particular consideration on shell and pair effects,the decay energy Q as well as the nucleon numbers(Z,N).Although the formula has relatively few parameters,it reproduces the experimentalβ^--decay half-lives of neutron-rich nuclei very well.The predicted half-lives for the r-process relevant nuclei obtained with the current formula serve as reliable input in the r-process model calculations.
基金supported by the National Research Foundation of Korea(NRF)Grant funded by the Korean Ministry of Education,Science,and Technology(No.NRF2020R1C1C1006029)。
文摘We examined the conditions of neutron density(n) and temperature(T9) 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-T9 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 Me V for the pairs of KTUY-AME and WS4-KTUY models,respectively. We found that these mass uncertainties result in a large discrepancy in the nn-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,81Cu,127Rh,132Cd,192Dy, and 197Tm, are highly recommended to be measured in radioactive-ion beam facilities for a better understanding of the r-process evolution.
