Big Bang nucleosynthesis(BBN)theory predicts the primordial abundances of the light elements^(2) H(referred to as deuterium,or D for short),^(3)He,^(4)He,and^(7) Li produced in the early universe.Among these,deuterium...Big Bang nucleosynthesis(BBN)theory predicts the primordial abundances of the light elements^(2) H(referred to as deuterium,or D for short),^(3)He,^(4)He,and^(7) Li produced in the early universe.Among these,deuterium,the first nuclide produced by BBN,is a key primordial material for subsequent reactions.To date,the uncertainty in predicted deuterium abundance(D/H)remains larger than the observational precision.In this study,the Monte Carlo simulation code PRIMAT was used to investigate the sensitivity of 11 important BBN reactions to deuterium abundance.We found that the reaction rate uncertainties of the four reactions d(d,n)^(3)He,d(d,p)t,d(p,γ)^(3)He,and p(n,γ)d had the largest influence on the calculated D/H uncertainty.Currently,the calculated D/H uncertainty cannot reach observational precision even with the recent LUNA precise d(p,γ)^(3) He rate.From the nuclear physics aspect,there is still room to largely reduce the reaction-rate uncertainties;hence,further measurements of the important reactions involved in BBN are still necessary.A photodisintegration experiment will be conducted at the Shanghai Laser Electron Gamma Source Facility to precisely study the deuterium production reaction of p(n,γ)d.展开更多
The Carmeli Cosmological Special Relativity theory (CSR) is used to study the universe at early times after the big bang. The universe temperature vs. time relation is developed from the mass density relation. It is s...The Carmeli Cosmological Special Relativity theory (CSR) is used to study the universe at early times after the big bang. The universe temperature vs. time relation is developed from the mass density relation. It is shown that CSR is well suited to analyze the nucleosynthesis of the light elements up to beryllium, equivalent to the standard model.展开更多
In our original paper, we outlined a new model of nucleosynthesis which began when a small percentage of the vacuum energy was converted primarily into neutron-antineutron pairs but with a very small excess of neutron...In our original paper, we outlined a new model of nucleosynthesis which began when a small percentage of the vacuum energy was converted primarily into neutron-antineutron pairs but with a very small excess of neutrons. In this paper, we present a detailed study of that original idea. We show that immediately after their inception, annihilation and charge exchange reactions proceeded at a very high rate and after an interval of no more than 10<sup>-12</sup> s, the matter/antimatter asymmetry of the universe and the present-day abundance of baryons had been established. The annihilations produced the high density of leptons critical for the weak interactions and the photons that make up the CMB. The model predicts a photon temperature in agreement with the present-day CMB value and also explains the origin of the CMB anisotropy spectrum. We also show how the nucleosynthesis density variations needed to explain all cosmic structures can resolve the difficulties that arise when trying to explain observed primordial element abundances in terms of a single-density universal model of nucleosynthesis.展开更多
We investigate nucleosynthesis inside the gamma-ray burst （GRB） accre- tion disks formed by the Type II collapsars. In these collapsars, the core collapse of massive stars first leads to the formation of a proto-neu...We investigate nucleosynthesis inside the gamma-ray burst （GRB） accre- tion disks formed by the Type II collapsars. In these collapsars, the core collapse of massive stars first leads to the formation of a proto-neutron star. After that, an out- ward moving shock triggers a successful supernova. However, the supernova ejecta lacks momentum and within a few seconds the newly formed neutron star gets trans- formed to a stellar mass black hole via massive fallback. The hydrodynamics of such an accretion disk formed from the fallback material of the supernova ejecta has been studied extensively in the past. We use these well-established hydrodynamic models for our accretion disk in order to understand nucleosynthesis, which is mainly ad- vection dominated in the outer regions. Neutrino cooling becomes important in the inner disk where the temperature and density are higher. The higher the accretion rate （M） is, the higher the density and temperature are in the disks. We deal with accre- tion disks with relatively low accretion rates： 0.001 Mo s-1 ~ 3）/~ 0.01 Mo S--1 and hence these disks are predominantly advection dominated. We use He-rich and Si- rich abundances as the initial condition of nucleosynthesis at the outer disk, and being equipped with the disk hydrodynamics and the nuclear network code, we study the abundance evolution as matter inflows and falls into the central object. We investigate the variation in the nucleosynthesis products in the disk with the change in the initial abundance at the outer disk and also with the change in the mass accretion rate. We report the synthesis of several unusual nuclei like 31p, 39K, 43Sc＇ 35C1 and various isotopes of titanium, vanadium, chromium, manganese and copper. We also confirm that isotopes of iron, cobalt, nickel, argon, calcium, sulphur and silicon get synthe- sized in the disk, as shown by previous authors. Much of these heavy elements thus synthesized are ejected from the disk via outflows and hence they should leave their signature in observed data.展开更多
We study the finite temperature and density effects on beta decay rates to compute their contributions to nucleosynthesis. QED type corrections to beta decay from the hot and dense background are estimated in terms of...We study the finite temperature and density effects on beta decay rates to compute their contributions to nucleosynthesis. QED type corrections to beta decay from the hot and dense background are estimated in terms of the statistical corrections to the self-mass of an electron. For this purpose, we re-examine the hot and dense background contributions to the electron mass and compute its effect to the beta decay rate, helium yield, energy density of the universe as well as the change in neutrino temperature from the first order contribution to the self-mass of electrons during these processes. We explicitly show that the thermal contribution to the helium abundance at T = m of a cooling universe (0.045 percent) is higher than the corresponding contribution to helium abundance of a heating universe (0.031 percent) due to the existence of hot fermions before the beginning of nucleosynthesis and their absence after the nucleosynthesis, in the early universe. Thermal contribution to helium abundance was a simple quadratic function of temperature, before and after the nucleosynthesis. However, this quadratic behavior was not the same before the decoupling temperature due to weak interactions;so the nucleosynthesis did not even start before the universe had cooled down to the neutrino decoupling temperatures and QED became a dominant theory in the presence of a high concentration of charged fermions. It is also explicitly shown that the chemical potential in the core of supermassive and superdense stars affect beta decay and their helium abundance but the background contributions depend on the ratio between temperature and chemical potential and not the chemical potential or temperature only. We calculate the hot and dense background contributions for m = T = μ. It has been noticed that temperature plays a role in regulating parameter in an extremely dense systems. Therefore, for extremely dense systems, temperature has to be large enough to get the expected value of helium production in the stellar cores.展开更多
Nucleosynthesis in advection-dominated accretion flow （ADAF） onto a black hole is proposed to be an important role in chemical evolution around compact stars. We investigate the nucleosynthesis in ADAF relevant for ...Nucleosynthesis in advection-dominated accretion flow （ADAF） onto a black hole is proposed to be an important role in chemical evolution around compact stars. We investigate the nucleosynthesis in ADAF relevant for a black hole of low mass, different from that of the self-similar solution. In particular, the presence of supersolar metal mass fractions of some isotopes seems to be associated with the known black hole nucleosynthesis in ADAF, which offers further evidence of diversity of the chemical enrichment.展开更多
The origin of boron in the solar system has not yet been clearly understood.We studied the light mass nuclear reactions and neutrino-induced reactions that play important roles in the nucleosynthesis of A=11 nuclei in...The origin of boron in the solar system has not yet been clearly understood.We studied the light mass nuclear reactions and neutrino-induced reactions that play important roles in the nucleosynthesis of A=11 nuclei in the core-collapse supernova(CCSN).We found that the production of A=11 nuclei,particularly^(11)C,is sensitive to the radioactive nuclear reaction^(11)C(α,p)^(14)N among many others.We calculated the upper and lower limits of the^(11)C(α,p)^(14)N rate by taking account of the low energy resonances above the threshold,which have not been included in the previous SN nucleosynthesis calculations.These resonance contributions significantly change the^(11)C abundance,which decays to^(11)B with a half-life of 20.34 m,and affects the resultant isotopic abundance ratio of^(11)B/^(10)B at Mr=3.78-4.4M⊙from which the presolar X grains could form.The^(11)B/^(10)B isotopic ratio measured in X grains can help to understand the origin of solar system boron and constrain still unknown neutrino mass hierarchy if the observational and theoretical uncertainties associated with these abundances are reduced.We emphasize that the further precise experiment of measuring the^(11)C(α,p)^(14)N reaction cross sections at the astrophysically interesting energies of Gamow window 0.23-1.24 MeV,which corresponds to the effective temperature T=0.2-1 GK,could clarify CCSN contribution to the solar^(11)B/^(10)B ratio.展开更多
Nuclear reaction studies on unstable isotopes can strongly help in improving our understanding of nucleosynthesis in stars.Indirect approaches to determining astrophysical reaction rates are increasingly common-place ...Nuclear reaction studies on unstable isotopes can strongly help in improving our understanding of nucleosynthesis in stars.Indirect approaches to determining astrophysical reaction rates are increasingly common-place and undergoing continuous refinement.Of particular interest is the use of such indirect techniques at storage rings,which,among other aspects,allow to recycle rare unstable beams.We propose to investigate the reaction rates of astrophysical interest using indirect methods(surrogate,Trojan horse,etc.)in reverse kinematics at the IMP-CAS storage ring.Long lived radioactive ion beams,produced remotely,can be accelerated,and made to interact with light targets.The proposed reactions are^(85)Kr(p,p’γ),^(85)Kr(d,pγ),constraining the neutron flux in an s-process branching point,^(79)Se(p,p’γ),^(79)Se(d,pγ),constraining the temperature in s-process nucleosyntheses,and^(59)Fe(d,pγ),constraining core collapse supernovae.展开更多
During the past few decades, it has become clear that the distribution, sizes, and masses of cosmic structures are best described as fractal rather than homogeneous. This means that an entirely different formalism is ...During the past few decades, it has become clear that the distribution, sizes, and masses of cosmic structures are best described as fractal rather than homogeneous. This means that an entirely different formalism is needed to replace the standard perturbation model of structure formation. Recently, we have been developing a model of cosmology that accounts for a large number of the observed properties of the universe. A key component of this model is that fractal structures that later regulated the creation of both matter and radiation came into existence during the initial Planck-era inflation. Initially, the vacuum was the only existence and since time, distance, and energy were uncertain, its only property, the curvature (or energy), was most likely distributed randomly. Everything that happened after the Planck era can be described by the known laws of physics so the remaining fundamental problem is to discover how such a random beginning could organize itself into the hierarchy of highly non-random self-similar structures on all length scales that are necessary to explain the existence of all cosmic structures. In this paper, we present a variation of the standard sandpile model that points to a solution. Incidental to our review of the distributions of cosmic structures, we discovered that the apparent transition from a fractal to a homogeneous distribution of structures at a distance of about 150 Mpc is a consequence of the finite size of the universe rather than a change in the underlying statistics of the distributions.展开更多
Within the context of the proton-neutron quasi-particle random phase approximation(pn-QRPA)model and TALYS v1.96 code,the radiative capture(^(99)Tc(n,γ)^(100)Tc)and stellar weak interaction(^(99)Tc→^(99)Ru+e^(−)+ν_...Within the context of the proton-neutron quasi-particle random phase approximation(pn-QRPA)model and TALYS v1.96 code,the radiative capture(^(99)Tc(n,γ)^(100)Tc)and stellar weak interaction(^(99)Tc→^(99)Ru+e^(−)+ν_(e))rates were computed during thermal pulses operating in asymptotic giant branch stars.The Maxwellian average cross-section(MACS)and neutron capture rates for the^(99)Tc(n,γ)^(100)Tc process are analyzed within the context of statistical code TALYS v1.96.The effect of nuclear level density(NLD)andγ-strength functions on MACS and neutron capture rates has been examined.The model-based computations for MACS provided an insightful contrast to prior investigated findings.The sensitivity of stellar weak interaction rates to different densities and temperatures is investigated using the pn-QRPA model.The impact of thermally populated excited states on electron emission(β^(−))rates in^(99)Tc is extensively examined.Additionally,a comparison is made between the study of the stellarβ^(−)decay rates and the thermal neutron capture rates.It is found that at T_(9)=0.26 the thermal neutron capture rates(λ_((n,γ)))and the temperature dependent stellarβ^(−)decay rates( λ_(β-))cross each other.However,at higher temperatures,theλ(n,γ)are found to be higher than λ_(β-).展开更多
Object LAMOST J020623.21+494127.9(program star) in the thin disk of the Milky Way is reported as a highly r-process-enhanced r-II star with [Eu/Fe] = +1.32 and [Fe/H] =-0.54. The chemical profile of the star reflects ...Object LAMOST J020623.21+494127.9(program star) in the thin disk of the Milky Way is reported as a highly r-process-enhanced r-II star with [Eu/Fe] = +1.32 and [Fe/H] =-0.54. The chemical profile of the star reflects the intrinsic composition of the gas cloud present at its birth. Using an abundance decomposition method, we fit25 elements from the abundance data set, including 10 heavy neutron-capture elements. We explore the astrophysical origin of the elements in this star through its abundance ratios and component ratios. We find that the contributions from the massive stars played a significant role in the production of light elements in the program star. Our analysis reveals that the heavy neutron-capture elements are produced purely by the main r-process. However, the adopted main r-process model does not adequately fit the observed data, suggesting another main r-process pattern may exist.展开更多
A kilonova is an optical-infrared transient powered by the radioactive decay of heavy nuclei from a binary neutron star merger.Its observational characteristics depend on the mass and the nuclide composition of merger...A kilonova is an optical-infrared transient powered by the radioactive decay of heavy nuclei from a binary neutron star merger.Its observational characteristics depend on the mass and the nuclide composition of merger ejecta,which are sensitive to the equation of state(EoS)of the neutron star.We use astrophysical conditions derived from different EoSs as nucleosynthesis inputs to explore the impact of various EoS on the r-process nucleosynthesis and the kilonova emission.Our results show that both the abundance patterns of merger ejecta and kilonova light curves are strongly dependent on the neutron star EoSs.Given the mass of two neutron stars,the merger with a softer EoS tends to generate a larger amount of ejected material,and may lead to a brighter kilonova peak luminosity.The relationship between the neutron star EoS and the peak luminosity provides a probe for constraining the properties of EoS in multi-messenger observations of neutron star mergers.展开更多
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
ISOTOPIC abundances of Xe were determined as two FeS separates of the Allende（C3V）car-bonaceous chondrite were heated,stepwise.A tracer Xe isotope was first produced in one sam-ple by <sup>130</sup>Te（n...ISOTOPIC abundances of Xe were determined as two FeS separates of the Allende（C3V）car-bonaceous chondrite were heated,stepwise.A tracer Xe isotope was first produced in one sam-ple by <sup>130</sup>Te（n,γ 2β<sup>-</sup>）<sup>131r</sup>Xe reaction to monitor the degassing of Xe from the sample.TheFeS melted at 950℃,releasing a spike of <sup>131r</sup>Xe and terrestrial-type Xe,Xe-T.This展开更多
We review our understanding of the nucleosynthesis that occurs in thermonuclear supernovae and their contribution to Galactic Chemical evolution. We discuss the prospects to improve the modeling of the nucleosynthesis...We review our understanding of the nucleosynthesis that occurs in thermonuclear supernovae and their contribution to Galactic Chemical evolution. We discuss the prospects to improve the modeling of the nucleosynthesis within simulations of these events.展开更多
In a self-consistent treatment, an LM-AGB TP model of HHe-burning and no-branch reaction passway for s-process from Fe-Bi with correlative reaction network from C-Ne is used to reproduce the enrichment of F, C and hea...In a self-consistent treatment, an LM-AGB TP model of HHe-burning and no-branch reaction passway for s-process from Fe-Bi with correlative reaction network from C-Ne is used to reproduce the enrichment of F, C and heavy elements in the surface of MS and S stars (with Tc). The growing of the core mass and the mass loss through steller winds are also considered. Comparisons between the computed correlation: {[F/O], C/O}; {[F/O], (s/Ti)} and that of the observations are then presented. It appears that fluorine and heavy elements can be synthesized where the nucleosynthesis events occur in a fit temperature range, and then are dredged up to the surface of the star. Because F production only occurs in a narrow temperature range, the synthesis events are sensitive to temperature. The observation of this case is discussed specially.展开更多
The ^(12)C+^(12)C reaction rate plays an essential role in stellar evolution and nucleosynthesis.Nevertheless,the uncertainties of this reaction rate are still large.We calculate a series of stellar evolution models w...The ^(12)C+^(12)C reaction rate plays an essential role in stellar evolution and nucleosynthesis.Nevertheless,the uncertainties of this reaction rate are still large.We calculate a series of stellar evolution models with the near solar abundance from the zero-age main-sequence through presupernova stages for initial masses of 20 M_(⊙) to 40 M_(⊙).The ^(12)C+^(12)C reaction rates from two different studies are used in our investigation.One is the rate obtained using the Trojan Horse Method(THM)by Tumino et al.[Nature 557(7707),687(2018)],and the other was obtained by Mukhamedzhanov et al.[Physical Review C 99(6),064618(2019)](Muk19).Then,comparisons of the nucleosynthesis and presupernova isotopic abundances are conducted.In particular,we find that in the C burning shell,models with the THM produce a smaller amount of ^(23)Na and some neutron-rich isotopes than Muk19.The difference in the abundance ratios of Na/Mg,S/Mg,Ar/Mg,and K/Mg between the two models are apparent.We compare Na/Mg obtained from our theoretical presupernovae models with Na/Mg in stellar atmospheres observed with high-resolution spectra as well as from the latest galactic chemical evolution model.Although Na/Mg obtained using the THM is within 2σ of the observed stellar ratio,the theoretical uncertainty on Na/Mg introduced by the uncertainty of the ^(12)C+^(12)C reaction rate is almost equivalent to the standard deviation of astronomical observations.Therefore,a more accurate ^(12)C+^(12)C reaction rate is crucial.展开更多
Revised October 2013 by B.D. Fields, （Univ. of Illinois） P. Molaro （Trieste Observatory） and S. Sarkar （Univ. of Oxford ＆ Niels Bohr Institute, Copenhagen）.
We investigate the impact of inelastic collisions between dark matter(DM)and heavy cosmic ray(CR)nuclei on CR propagation.We approximate the fragmentation cross-sections for DM-CR collisions using collider-measured pr...We investigate the impact of inelastic collisions between dark matter(DM)and heavy cosmic ray(CR)nuclei on CR propagation.We approximate the fragmentation cross-sections for DM-CR collisions using collider-measured proton-nuclei scattering cross-sections,allowing us to assess how these collisions affect the spectra of CR boron and carbon.We derive new CR spectra from DM-CR collisions by incorporating their cross-sections into the source terms and solving the diffusion equation for the complete network of reactions involved in generating secondary species.In a specific example with a coupling strength of b_(χ)=0.1 and a DM mass of m_(χ)=0.1 GeV,considering a simplified scenario where DM interacts exclusively with oxygen,a notable modification in the boron-to-carbon spectrum due to the DM-CR interaction is observed.Particularly,the peak within the spectrum,spanning from 0.1 to 10 GeV,experiences an enhancement of approximately 1.5 times.However,in a more realistic scenario where DM particles interact with all CRs,this peak can be amplified to twice its original value.Utilizing the latest data from AMS-02 and DAMPE on the boron-to-carbon ratio,we estimate a 95%upper limit for the effective inelastic cross-section of DM-proton as a function of DM mass.Our findings reveal that at m_(χ)?2 MeV,the effective inelastic cross-section between DM and protons must be less than O(10^(-32))cm^(2).展开更多
In a recent series of papers, we introduced a new model of nucleosynthesis in which the matter content of the universe came into existence at a time of about 4 × 10<sup>-5</sup> s. At that time, a sma...In a recent series of papers, we introduced a new model of nucleosynthesis in which the matter content of the universe came into existence at a time of about 4 × 10<sup>-5</sup> s. At that time, a small percentage of the vacuum energy was converted into neutron/antineutron pairs with a very small excess of neutrons. This process was regulated by an imprint that was established in the vacuum during an initial Plank-era inflation. Immediately after their inception, annihilation and charge exchange reactions proceeded at a very high rate and ran to completion after an interval of about 10<sup>-11</sup> s. By then, all the antibaryons had disappeared thereby establishing the matter/antimatter asymmetry of the universe. What remained were very high densities of mesons and leptons, somewhat lower densities of protons and neutrons, and finally, the very high density of photons that eventually became the CMB. The density of matter so created varied from one location to another in such a manner as to account for all cosmic structures and because the energy density of the photons varied in proportion to that of the matter, the CMB-to-be came into existence with an anisotropic spectrum already in place. For structures, the size of galaxy clusters, the initial anisotropy magnitudes were on the order of 25%. In this paper, we will follow the subsequent evolution of the photons and show that this model predicts with accuracy the temperature of the warmest anisotropies in the observed CMB spectrum. .展开更多
基金supported by the National Key R&D Program of China(No.2022YFA1602401)by the National Natural Science Foundation of China(No.11825504)。
文摘Big Bang nucleosynthesis(BBN)theory predicts the primordial abundances of the light elements^(2) H(referred to as deuterium,or D for short),^(3)He,^(4)He,and^(7) Li produced in the early universe.Among these,deuterium,the first nuclide produced by BBN,is a key primordial material for subsequent reactions.To date,the uncertainty in predicted deuterium abundance(D/H)remains larger than the observational precision.In this study,the Monte Carlo simulation code PRIMAT was used to investigate the sensitivity of 11 important BBN reactions to deuterium abundance.We found that the reaction rate uncertainties of the four reactions d(d,n)^(3)He,d(d,p)t,d(p,γ)^(3)He,and p(n,γ)d had the largest influence on the calculated D/H uncertainty.Currently,the calculated D/H uncertainty cannot reach observational precision even with the recent LUNA precise d(p,γ)^(3) He rate.From the nuclear physics aspect,there is still room to largely reduce the reaction-rate uncertainties;hence,further measurements of the important reactions involved in BBN are still necessary.A photodisintegration experiment will be conducted at the Shanghai Laser Electron Gamma Source Facility to precisely study the deuterium production reaction of p(n,γ)d.
文摘The Carmeli Cosmological Special Relativity theory (CSR) is used to study the universe at early times after the big bang. The universe temperature vs. time relation is developed from the mass density relation. It is shown that CSR is well suited to analyze the nucleosynthesis of the light elements up to beryllium, equivalent to the standard model.
文摘In our original paper, we outlined a new model of nucleosynthesis which began when a small percentage of the vacuum energy was converted primarily into neutron-antineutron pairs but with a very small excess of neutrons. In this paper, we present a detailed study of that original idea. We show that immediately after their inception, annihilation and charge exchange reactions proceeded at a very high rate and after an interval of no more than 10<sup>-12</sup> s, the matter/antimatter asymmetry of the universe and the present-day abundance of baryons had been established. The annihilations produced the high density of leptons critical for the weak interactions and the photons that make up the CMB. The model predicts a photon temperature in agreement with the present-day CMB value and also explains the origin of the CMB anisotropy spectrum. We also show how the nucleosynthesis density variations needed to explain all cosmic structures can resolve the difficulties that arise when trying to explain observed primordial element abundances in terms of a single-density universal model of nucleosynthesis.
基金partly supported by the ISRO grant ISRO/RES/2/367/10-11
文摘We investigate nucleosynthesis inside the gamma-ray burst （GRB） accre- tion disks formed by the Type II collapsars. In these collapsars, the core collapse of massive stars first leads to the formation of a proto-neutron star. After that, an out- ward moving shock triggers a successful supernova. However, the supernova ejecta lacks momentum and within a few seconds the newly formed neutron star gets trans- formed to a stellar mass black hole via massive fallback. The hydrodynamics of such an accretion disk formed from the fallback material of the supernova ejecta has been studied extensively in the past. We use these well-established hydrodynamic models for our accretion disk in order to understand nucleosynthesis, which is mainly ad- vection dominated in the outer regions. Neutrino cooling becomes important in the inner disk where the temperature and density are higher. The higher the accretion rate （M） is, the higher the density and temperature are in the disks. We deal with accre- tion disks with relatively low accretion rates： 0.001 Mo s-1 ~ 3）/~ 0.01 Mo S--1 and hence these disks are predominantly advection dominated. We use He-rich and Si- rich abundances as the initial condition of nucleosynthesis at the outer disk, and being equipped with the disk hydrodynamics and the nuclear network code, we study the abundance evolution as matter inflows and falls into the central object. We investigate the variation in the nucleosynthesis products in the disk with the change in the initial abundance at the outer disk and also with the change in the mass accretion rate. We report the synthesis of several unusual nuclei like 31p, 39K, 43Sc＇ 35C1 and various isotopes of titanium, vanadium, chromium, manganese and copper. We also confirm that isotopes of iron, cobalt, nickel, argon, calcium, sulphur and silicon get synthe- sized in the disk, as shown by previous authors. Much of these heavy elements thus synthesized are ejected from the disk via outflows and hence they should leave their signature in observed data.
文摘We study the finite temperature and density effects on beta decay rates to compute their contributions to nucleosynthesis. QED type corrections to beta decay from the hot and dense background are estimated in terms of the statistical corrections to the self-mass of an electron. For this purpose, we re-examine the hot and dense background contributions to the electron mass and compute its effect to the beta decay rate, helium yield, energy density of the universe as well as the change in neutrino temperature from the first order contribution to the self-mass of electrons during these processes. We explicitly show that the thermal contribution to the helium abundance at T = m of a cooling universe (0.045 percent) is higher than the corresponding contribution to helium abundance of a heating universe (0.031 percent) due to the existence of hot fermions before the beginning of nucleosynthesis and their absence after the nucleosynthesis, in the early universe. Thermal contribution to helium abundance was a simple quadratic function of temperature, before and after the nucleosynthesis. However, this quadratic behavior was not the same before the decoupling temperature due to weak interactions;so the nucleosynthesis did not even start before the universe had cooled down to the neutrino decoupling temperatures and QED became a dominant theory in the presence of a high concentration of charged fermions. It is also explicitly shown that the chemical potential in the core of supermassive and superdense stars affect beta decay and their helium abundance but the background contributions depend on the ratio between temperature and chemical potential and not the chemical potential or temperature only. We calculate the hot and dense background contributions for m = T = μ. It has been noticed that temperature plays a role in regulating parameter in an extremely dense systems. Therefore, for extremely dense systems, temperature has to be large enough to get the expected value of helium production in the stellar cores.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11547041,11403007,11673007,11643007,11333004,U1531130,11673059,11390374 and 11521303the Chinese Academy of Sciences under Grant Nos KJZD-EW-M06-01and QYZDB-SSW-SYS001
文摘Nucleosynthesis in advection-dominated accretion flow （ADAF） onto a black hole is proposed to be an important role in chemical evolution around compact stars. We investigate the nucleosynthesis in ADAF relevant for a black hole of low mass, different from that of the self-similar solution. In particular, the presence of supersolar metal mass fractions of some isotopes seems to be associated with the known black hole nucleosynthesis in ADAF, which offers further evidence of diversity of the chemical enrichment.
基金under the support of CSC scholarship from the Ministry of Education of China during his stay at the National Astronomical Observatory of Japan(NAOJ)partly supported by the National Key R&D Program of China(2022YFA1602401)+1 种基金the National Natural Science Foundation of China(12335009,12435010)supported by JSPS KAKENHI(19K03883,23H01181,23K25877)from the Ministry of Education,Culture,Sports,Science and Technology(MEXT)of Japan。
文摘The origin of boron in the solar system has not yet been clearly understood.We studied the light mass nuclear reactions and neutrino-induced reactions that play important roles in the nucleosynthesis of A=11 nuclei in the core-collapse supernova(CCSN).We found that the production of A=11 nuclei,particularly^(11)C,is sensitive to the radioactive nuclear reaction^(11)C(α,p)^(14)N among many others.We calculated the upper and lower limits of the^(11)C(α,p)^(14)N rate by taking account of the low energy resonances above the threshold,which have not been included in the previous SN nucleosynthesis calculations.These resonance contributions significantly change the^(11)C abundance,which decays to^(11)B with a half-life of 20.34 m,and affects the resultant isotopic abundance ratio of^(11)B/^(10)B at Mr=3.78-4.4M⊙from which the presolar X grains could form.The^(11)B/^(10)B isotopic ratio measured in X grains can help to understand the origin of solar system boron and constrain still unknown neutrino mass hierarchy if the observational and theoretical uncertainties associated with these abundances are reduced.We emphasize that the further precise experiment of measuring the^(11)C(α,p)^(14)N reaction cross sections at the astrophysically interesting energies of Gamow window 0.23-1.24 MeV,which corresponds to the effective temperature T=0.2-1 GK,could clarify CCSN contribution to the solar^(11)B/^(10)B ratio.
文摘Nuclear reaction studies on unstable isotopes can strongly help in improving our understanding of nucleosynthesis in stars.Indirect approaches to determining astrophysical reaction rates are increasingly common-place and undergoing continuous refinement.Of particular interest is the use of such indirect techniques at storage rings,which,among other aspects,allow to recycle rare unstable beams.We propose to investigate the reaction rates of astrophysical interest using indirect methods(surrogate,Trojan horse,etc.)in reverse kinematics at the IMP-CAS storage ring.Long lived radioactive ion beams,produced remotely,can be accelerated,and made to interact with light targets.The proposed reactions are^(85)Kr(p,p’γ),^(85)Kr(d,pγ),constraining the neutron flux in an s-process branching point,^(79)Se(p,p’γ),^(79)Se(d,pγ),constraining the temperature in s-process nucleosyntheses,and^(59)Fe(d,pγ),constraining core collapse supernovae.
文摘During the past few decades, it has become clear that the distribution, sizes, and masses of cosmic structures are best described as fractal rather than homogeneous. This means that an entirely different formalism is needed to replace the standard perturbation model of structure formation. Recently, we have been developing a model of cosmology that accounts for a large number of the observed properties of the universe. A key component of this model is that fractal structures that later regulated the creation of both matter and radiation came into existence during the initial Planck-era inflation. Initially, the vacuum was the only existence and since time, distance, and energy were uncertain, its only property, the curvature (or energy), was most likely distributed randomly. Everything that happened after the Planck era can be described by the known laws of physics so the remaining fundamental problem is to discover how such a random beginning could organize itself into the hierarchy of highly non-random self-similar structures on all length scales that are necessary to explain the existence of all cosmic structures. In this paper, we present a variation of the standard sandpile model that points to a solution. Incidental to our review of the distributions of cosmic structures, we discovered that the apparent transition from a fractal to a homogeneous distribution of structures at a distance of about 150 Mpc is a consequence of the finite size of the universe rather than a change in the underlying statistics of the distributions.
基金the financial support of the Higher Education Commission Pakistan through project number 20-15394/NRPU/R&D/HEC/2021.
文摘Within the context of the proton-neutron quasi-particle random phase approximation(pn-QRPA)model and TALYS v1.96 code,the radiative capture(^(99)Tc(n,γ)^(100)Tc)and stellar weak interaction(^(99)Tc→^(99)Ru+e^(−)+ν_(e))rates were computed during thermal pulses operating in asymptotic giant branch stars.The Maxwellian average cross-section(MACS)and neutron capture rates for the^(99)Tc(n,γ)^(100)Tc process are analyzed within the context of statistical code TALYS v1.96.The effect of nuclear level density(NLD)andγ-strength functions on MACS and neutron capture rates has been examined.The model-based computations for MACS provided an insightful contrast to prior investigated findings.The sensitivity of stellar weak interaction rates to different densities and temperatures is investigated using the pn-QRPA model.The impact of thermally populated excited states on electron emission(β^(−))rates in^(99)Tc is extensively examined.Additionally,a comparison is made between the study of the stellarβ^(−)decay rates and the thermal neutron capture rates.It is found that at T_(9)=0.26 the thermal neutron capture rates(λ_((n,γ)))and the temperature dependent stellarβ^(−)decay rates( λ_(β-))cross each other.However,at higher temperatures,theλ(n,γ)are found to be higher than λ_(β-).
基金supported by the National Key Basic R&D Program of China No. 2024YFA1611903the National Natural Science Foundation of China (NSFC, Grant No. 12173013)+2 种基金the project of Hebei provincial department of science and technology under the grant No. 226Z7604Gthe Hebei NSF (No. A2021205006)the China Manned Space Project for funding support of this study
文摘Object LAMOST J020623.21+494127.9(program star) in the thin disk of the Milky Way is reported as a highly r-process-enhanced r-II star with [Eu/Fe] = +1.32 and [Fe/H] =-0.54. The chemical profile of the star reflects the intrinsic composition of the gas cloud present at its birth. Using an abundance decomposition method, we fit25 elements from the abundance data set, including 10 heavy neutron-capture elements. We explore the astrophysical origin of the elements in this star through its abundance ratios and component ratios. We find that the contributions from the massive stars played a significant role in the production of light elements in the program star. Our analysis reveals that the heavy neutron-capture elements are produced purely by the main r-process. However, the adopted main r-process model does not adequately fit the observed data, suggesting another main r-process pattern may exist.
基金supported by the National Natural Science Foundation of China(NSFC,grant Nos.12403043,12347172,and 12133003)M.H.C.also acknowledges support from the China Postdoctoral Science Foundation(grant Nos.GZB20230029 and 2024M750057)supported by the Guangxi Talent Program(Highland of Innovation Talents).
文摘A kilonova is an optical-infrared transient powered by the radioactive decay of heavy nuclei from a binary neutron star merger.Its observational characteristics depend on the mass and the nuclide composition of merger ejecta,which are sensitive to the equation of state(EoS)of the neutron star.We use astrophysical conditions derived from different EoSs as nucleosynthesis inputs to explore the impact of various EoS on the r-process nucleosynthesis and the kilonova emission.Our results show that both the abundance patterns of merger ejecta and kilonova light curves are strongly dependent on the neutron star EoSs.Given the mass of two neutron stars,the merger with a softer EoS tends to generate a larger amount of ejected material,and may lead to a brighter kilonova peak luminosity.The relationship between the neutron star EoS and the peak luminosity provides a probe for constraining the properties of EoS in multi-messenger observations of neutron star mergers.
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.
文摘ISOTOPIC abundances of Xe were determined as two FeS separates of the Allende（C3V）car-bonaceous chondrite were heated,stepwise.A tracer Xe isotope was first produced in one sam-ple by <sup>130</sup>Te（n,γ 2β<sup>-</sup>）<sup>131r</sup>Xe reaction to monitor the degassing of Xe from the sample.TheFeS melted at 950℃,releasing a spike of <sup>131r</sup>Xe and terrestrial-type Xe,Xe-T.This
文摘We review our understanding of the nucleosynthesis that occurs in thermonuclear supernovae and their contribution to Galactic Chemical evolution. We discuss the prospects to improve the modeling of the nucleosynthesis within simulations of these events.
基金Project supported by the National Natural Science Foundation of China and the Climbing Project of China.
文摘In a self-consistent treatment, an LM-AGB TP model of HHe-burning and no-branch reaction passway for s-process from Fe-Bi with correlative reaction network from C-Ne is used to reproduce the enrichment of F, C and heavy elements in the surface of MS and S stars (with Tc). The growing of the core mass and the mass loss through steller winds are also considered. Comparisons between the computed correlation: {[F/O], C/O}; {[F/O], (s/Ti)} and that of the observations are then presented. It appears that fluorine and heavy elements can be synthesized where the nucleosynthesis events occur in a fit temperature range, and then are dredged up to the surface of the star. Because F production only occurs in a narrow temperature range, the synthesis events are sensitive to temperature. The observation of this case is discussed specially.
基金Supported by the National Natural Science Foundation of China(11988101,11890694)the National Key R&D Program of China(2019YFA0405502)K.Nomoto is supported by the World Premier International Research Center Initiative(WPI),MEXT,Japan,and the Japan Society for the Promotion of Science(JSPS)KAKENHIgrant(JP17K05382,JP20K04024,JP21H04499)。
文摘The ^(12)C+^(12)C reaction rate plays an essential role in stellar evolution and nucleosynthesis.Nevertheless,the uncertainties of this reaction rate are still large.We calculate a series of stellar evolution models with the near solar abundance from the zero-age main-sequence through presupernova stages for initial masses of 20 M_(⊙) to 40 M_(⊙).The ^(12)C+^(12)C reaction rates from two different studies are used in our investigation.One is the rate obtained using the Trojan Horse Method(THM)by Tumino et al.[Nature 557(7707),687(2018)],and the other was obtained by Mukhamedzhanov et al.[Physical Review C 99(6),064618(2019)](Muk19).Then,comparisons of the nucleosynthesis and presupernova isotopic abundances are conducted.In particular,we find that in the C burning shell,models with the THM produce a smaller amount of ^(23)Na and some neutron-rich isotopes than Muk19.The difference in the abundance ratios of Na/Mg,S/Mg,Ar/Mg,and K/Mg between the two models are apparent.We compare Na/Mg obtained from our theoretical presupernovae models with Na/Mg in stellar atmospheres observed with high-resolution spectra as well as from the latest galactic chemical evolution model.Although Na/Mg obtained using the THM is within 2σ of the observed stellar ratio,the theoretical uncertainty on Na/Mg introduced by the uncertainty of the ^(12)C+^(12)C reaction rate is almost equivalent to the standard deviation of astronomical observations.Therefore,a more accurate ^(12)C+^(12)C reaction rate is crucial.
文摘Revised October 2013 by B.D. Fields, （Univ. of Illinois） P. Molaro （Trieste Observatory） and S. Sarkar （Univ. of Oxford ＆ Niels Bohr Institute, Copenhagen）.
基金supported by the National Key Research and Development Program of China(2022YFF0503304,2020YFC2201600,2018YFA0404504 and 2018YFA0404601)the Ministry of Science and Technology of China(2020SKA0110402,2020SKA0110401 and 2020SKA0110100)+4 种基金the National Natural Science Foundation of China(11890691,12205388 and 12220101003)the CAS Project for Young Scientists in Basic Research(YSBR-061,YSBR-092)the China Manned Space Project with No.CMS-CSST-2021(A02,A03 and B01)the Major Key Project of PCLthe 111 project(B20019)。
文摘We investigate the impact of inelastic collisions between dark matter(DM)and heavy cosmic ray(CR)nuclei on CR propagation.We approximate the fragmentation cross-sections for DM-CR collisions using collider-measured proton-nuclei scattering cross-sections,allowing us to assess how these collisions affect the spectra of CR boron and carbon.We derive new CR spectra from DM-CR collisions by incorporating their cross-sections into the source terms and solving the diffusion equation for the complete network of reactions involved in generating secondary species.In a specific example with a coupling strength of b_(χ)=0.1 and a DM mass of m_(χ)=0.1 GeV,considering a simplified scenario where DM interacts exclusively with oxygen,a notable modification in the boron-to-carbon spectrum due to the DM-CR interaction is observed.Particularly,the peak within the spectrum,spanning from 0.1 to 10 GeV,experiences an enhancement of approximately 1.5 times.However,in a more realistic scenario where DM particles interact with all CRs,this peak can be amplified to twice its original value.Utilizing the latest data from AMS-02 and DAMPE on the boron-to-carbon ratio,we estimate a 95%upper limit for the effective inelastic cross-section of DM-proton as a function of DM mass.Our findings reveal that at m_(χ)?2 MeV,the effective inelastic cross-section between DM and protons must be less than O(10^(-32))cm^(2).
文摘In a recent series of papers, we introduced a new model of nucleosynthesis in which the matter content of the universe came into existence at a time of about 4 × 10<sup>-5</sup> s. At that time, a small percentage of the vacuum energy was converted into neutron/antineutron pairs with a very small excess of neutrons. This process was regulated by an imprint that was established in the vacuum during an initial Plank-era inflation. Immediately after their inception, annihilation and charge exchange reactions proceeded at a very high rate and ran to completion after an interval of about 10<sup>-11</sup> s. By then, all the antibaryons had disappeared thereby establishing the matter/antimatter asymmetry of the universe. What remained were very high densities of mesons and leptons, somewhat lower densities of protons and neutrons, and finally, the very high density of photons that eventually became the CMB. The density of matter so created varied from one location to another in such a manner as to account for all cosmic structures and because the energy density of the photons varied in proportion to that of the matter, the CMB-to-be came into existence with an anisotropic spectrum already in place. For structures, the size of galaxy clusters, the initial anisotropy magnitudes were on the order of 25%. In this paper, we will follow the subsequent evolution of the photons and show that this model predicts with accuracy the temperature of the warmest anisotropies in the observed CMB spectrum. .
