The cooling strength of the Urca pair, ^63 Fe– ^63 Mn, exhibits an extensive range of variation due to the uncertainty in the spin parity of the ground state of ^63 Fe. To investigate the cooling effect of this Urca pair on the thermal evolution of neutron star crusts, we performed simulations on neutron star structure and evolution under various spin-parity assignment scenarios. When adopting recently evaluated nuclear data, ^63 Fe– ^63 Mn emerges as one of the strongest Urca pairs. In the case of MAXI J0556-332, ^63 Fe– ^63 Mn is the only pair above the shallow heating layer, significantly impacting the cooling curve and the superburst ignition. Moreover, the constraint on the past nucleosynthesis reduced to one-quarter of its original value, falling within three decades, which enables the validation of nuclear reaction theories in the outer layers of neutron stars. Our results highlight the need for more precise measurements of the β ^− decay of ^63 Mn to better determine the Urca cooling effect of the ^63 Fe– ^63 Mn pair in accreted neutron star crusts.

Highly oriented pyrolytic graphite (HOPG) is frequently adopted as the reaction target in ^12 C+ ^12 C fusion reaction experiments owing to its superior purity. In this study, we investigate the reaction yield dependence on the accumulated beam dose on HOPG target using a novel detection system consisting of a time-projection chamber and silicon array. The reaction yields are significantly reduced under intense beam bombardment owing to radiation damage to the HOPG surface. The α _0 and p_0,1 yields decrease by 51.5 ^12 C ^2+ beam dose accumulates at 5 C. Using the novel detection system and HOPG target, the α _0 yield is determined to be 2.68^+4.69_-1.69 × 10^-17 / ^12 C after correcting for the yield loss due to radiation damage. Our result represents the highest sensitivity achieved to date in direct measurements of ^12 C( ^12 C, α _0 ) ^20 Ne.

We investigate the Gamow-Teller (GT) and spin-dipole (SD) transitions in the direction of 0+ decay for neutron-rich N = 50 nucleus 80Zn and N = 82 nucleus 126Ru, which are important for deleptonization phase in core-collapse supernova, at T = 0, 1, 2 MeV with finite-temperature proton-neutron relativistic (quasiparticle) random-phase approximation. At zero temperature, the GT+ transitions for 80Zn and 126Ru are almost completely Pauli blocked because one more extra shell is occupied for neutrons than that for protons. With increasing temperature to even 2 MeV, the thermal excitation still cannot open up GT+ transitions with strong strength. The SD+ transitions in 80Zn are mildly affected by temperature, which means the experimental data measured at the laboratory can provide useful information for transitions in an astrophysical environment. However, for SD+ transitions in 126Ru, the transition energies have a decrease of about 2 MeV from zero temperature to T = 1 MeV due to the collapse of pairing gap of transition orbitals. The total strength in T+ channel decreases with increasing temperature for both GT and SD transitions, due to the suppression of their transition strength induced by temperature effects.

X-ray bursts are among the brightest stellar objects frequently observed in the sky by space-based telescopes. A type-I X-ray burst is understood as a violent thermonuclear explosion on the surface of a neutron star, accreting matter from a companion star in a binary system. The bursts are powered by a nuclear reaction sequence known as the rapid proton capture process (rp process), which involves hundreds of exotic neutron-deficient nuclides. At so-called waiting-point nuclides, the process stalls until a slower β + decay enables a bypass. One of the handful of rp process waiting-point nuclides is 64 Ge, which plays a decisive role in matter flow and therefore the produced X-ray flux. Here we report precision measurements of the masses of 63 Ge, 64,65 As and 66,67 Se—the relevant nuclear masses around the waiting-point 64 Ge—and use them as inputs for X-ray burst model calculations. We obtain the X-ray burst light curve to constrain the neutron-star compactness, and suggest that the distance to the X-ray burster GS 1826–24 needs to be increased by about 6.5% to match astronomical observations. The nucleosynthesis results affect the thermal structure of accreting neutron stars, which will subsequently modify the calculations of associated observables.

We investigate the Gamow-Teller (GT) and spin-dipole (SD) transitions in the direction of ${\ensuremath{\beta}}^{+}$ decay for neutron-rich $N=50$ nucleus $^{80}\mathrm{Zn}$ and $N=82$ nucleus $^{126}\mathrm{Ru}$, which are important for deleptonization phase in core-collapse supernova, at $T=0,\phantom{\rule{0.16em}{0ex}}1,\phantom{\rule{0.16em}{0ex}}2$ MeV with finite-temperature proton-neutron relativistic (quasiparticle) random-phase approximation. At zero temperature, the ${\mathrm{GT}}^{+}$ transitions for $^{80}\mathrm{Zn}$ and $^{126}\mathrm{Ru}$ are almost completely Pauli blocked because one more extra shell is occupied for neutrons than that for protons. With increasing temperature to even 2 MeV, the thermal excitation still cannot open up ${\mathrm{GT}}^{+}$ transitions with strong strength. The ${\mathrm{SD}}^{+}$ transitions in $^{80}\mathrm{Zn}$ are mildly affected by temperature, which means the experimental data measured at the laboratory can provide useful information for transitions in an astrophysical environment. However, for ${\mathrm{SD}}^{+}$ transitions in $^{126}\mathrm{Ru}$, the transition energies have a decrease of about 2 MeV from zero temperature to $T=1$ MeV due to the collapse of pairing gap of transition orbitals. The total strength in ${T}^{+}$ channel decreases with increasing temperature for both GT and SD transitions, due to the suppression of their transition strength induced by temperature effects.

The C-12+C-12 fusion reaction was studied in the range of E-c.m.=8.9 to 21 MeV using the active-target Time Projection Chamber. With full information on all tracks of the reaction products, cross sections of the C-12(C-12, Be-8)O-16(g.s.) channel and the C-12(C-12, 3 alpha)C-12 channel could be measured down to the level of a few milibarns. The C-12(C-12, Be-8)O-16(g.s.) reaction channel was determined to be 10(-8)(+24) mb at E-c.m. = 11.1 MeV, supporting the direct alpha transfer reaction mechanism. The C-12(C-12, 3 alpha)C-12 reaction channel was studied for the first time using an exclusive measurement. Our result does not confirm the anomaly behavior reported in the previous inclusive measurement by Kolata et al. [Phys. Rev. C 21, 579 (1980)]. Our comparisons with statistical model calculations suggest that the 3 alpha channel is dominated by the fusion evaporation process at E-c.m. > 19 MeV. The additional contribution of the 3 alpha channel increases the fusion reaction cross section by 10% at energies above 20 MeV. We also find that an additional reaction mechanism is needed to explain the measured cross section at E-c.m. < 15 MeV at which point the statistical model prediction vanishes.

The 12 C+ 12 C fusion reaction was studied in the range of E c.m. =8.9 to 21 MeV using the active-target Time Projection Chamber.With full information on all tracks of the reaction products,cross sections of the 12 C( 12 C,~8 Be) 16 O g.s. channel and the 12 C( 12 C,3 a) 12 C channel could be measured down to the level of a few milibarns.The 12 C( 12 C,~8 Be) 16 O g.s. reaction channel was determined to be 10 -8 +2 4 mb at E c.m. =11.1 MeV,supporting the direct a transfer reaction mechanism.The 12 C( 12 C,3α) 12 C reaction channel was studied for the first time using an exclusive measurement.Our result does not confirm the anomaly behavior reported in the previous inclusive measurement by Kolata et al.[Phys.Rev.C 21,579（1980）].Our comparisons with statistical model calculations suggest that the 3 a channel is dominated by the fusion evaporation process at E c.m. ＞ 19 MeV.The additional contribution of the 3 a channel increases the fusion reaction cross section by 10% at energies above 20 MeV.We also find that an additional reaction mechanism is needed to explain the measured cross section at E c.m. ＜15 MeV at which point the statistical model prediction vanishes.

Underground Nuclear Astrophysics Experiment in China (JUNA) has been commissioned by taking the advantage of the ultra-low background in Jinping underground lab. High current mA level 400 KV accelerator with an ECR source and BGO detectors were commissioned. JUNA studies directly a number of nuclear reactions important to hydrostatic stellar evolution at their relevant stellar energies. In the first quarter of 2021, JUNA performed the direct measurements of 25Mg(p,γ)26Al, 19F(p,α)16O, 13C(α,n)16O and 12C(α,γ)16O near the Gamow window. The experimental results reflect the potential of JUNA with higher statistics, precision and sensitivity of the data. The preliminary results of JUNA experiment and future plan are given.

A low-background neutron detector array was developed to measure the cross section of the $$^{13}$$ C( $$\alpha$$ ,n) $$^{16}$$ O reaction, which is the neutron source for the s-process in AGB stars, in the Gamow window ( $$E_\text {c.m.}$$ = 190 ± 40 keV) at the China Jinping Underground Laboratory (CJPL). The detector array consists of 24 $$^{3}$$ He proportional counters embedded in a polyethylene cube. Owing to the deep underground location and a borated polyethylene shield around the detector array, a low background of 4.5(2)/h was achieved. The $$^{51}$$ V(p, n) $$^{51}$$ Cr reaction was used to determine the neutron detection efficiency of the array for neutrons with energies $$E_\text {n}<$$ 1 MeV. Geant4 simulations are shown to effectively reproduce the experimental results. They were used to extrapolate the detection efficiency to higher energies for neutrons emitted in the $$^{13}$$ C( $$\alpha$$ ,n) $$^{16}$$ O reaction. The theoretical angular distributions of the $$^{13}$$ C( $$\alpha$$ ,n) $$^{16}$$ O reaction were shown to be important in the estimation of the uncertainties of the detection efficiency.

The cosmic evolution of the chemical elements from the Big Bang to the present time is driven by nuclear fusion reactions inside stars and stellar explosions. A cycle of matter recurrently re-processes metal-enriched stellar ejecta into the next generation of stars. The study of cosmic nucleosynthesis and this matter cycle requires the understanding of the physics of nuclear reactions, of the conditions at which the nuclear reactions are activated inside the stars and stellar explosions, of the stellar ejection mechanisms through winds and explosions, and of the transport of the ejecta towards the next cycle, from hot plasma to cold, star-forming gas. Due to the long timescales of stellar evolution, and because of the infrequent occurrence of stellar explosions, observational studies are challenging, as they have biases in time and space as well as different sensitivities related to the various astronomical methods. Here, we describe in detail the astrophysical and nuclear-physical processes involved in creating two radioactive isotopes useful in such studies, $^{26}\mathrm{Al}$ and $^{60}\mathrm{Fe}$ . Due to their radioactive lifetime of the order of a million years, these isotopes are suitable to characterise simultaneously the processes of nuclear fusion reactions and of interstellar transport. We describe and discuss the nuclear reactions involved in the production and destruction of $^{26}\mathrm{Al}$ and $^{60}\mathrm{Fe}$ , the key characteristics of the stellar sites of their nucleosynthesis and their interstellar journey after ejection from the nucleosynthesis sites. This allows us to connect the theoretical astrophysical aspects to the variety of astronomical messengers presented here, from stardust and cosmic-ray composition measurements, through observation of $\gamma$ rays produced by radioactivity, to material deposited in deep-sea ocean crusts and to the inferred composition of the first solids that have formed in the Solar System. We show that considering measurements of the isotopic ratio of $^{26}\mathrm{Al}$ to $^{60}\mathrm{Fe}$ eliminate some of the unknowns when interpreting astronomical results, and discuss the lessons learned from these two isotopes on cosmic chemical evolution. This review paper has emerged from an ISSI-BJ Team project in 2017–2019, bringing together nuclear physicists, astronomers, and astrophysicists in this inter-disciplinary discussion.

The cosmic evolution of the chemical elements from the Big Bang to the present time is driven by nuclear fusion reactions inside stars and stellar explosions. A cycle of matter recurrently re-processes metal-enriched stellar ejecta into the next generation of stars. The study of cosmic nucleosynthesis and of this matter cycle requires the understanding of the physics of nuclear reactions, of the conditions at which the nuclear reactions are activated inside the stars and stellar explosions, of the stellar ejection mechanisms through winds and explosions, and of the transport of the ejecta towards the next cycle, from hot plasma to cold, star-forming gas. Due to the long timescales of stellar evolution, and because of the infrequent occurrence of stellar explosions, observational studies are challenging. Due to their radioactive lifetime of million years, the 26Al and 60Fe isotopes are suitable to characterise simultaneously the processes of nuclear fusion reactions and of interstellar transport. We describe and discuss the nuclear reactions involved in the production and destruction of 26Al and 60Fe, the key characteristics of the stellar sites of their nucleosynthesis and their interstellar journey after ejection from the nucleosynthesis sites. We connect the theoretical astrophysical aspects to the variety of astronomical messengers, from stardust and cosmic-ray composition measurements, through observation of gamma rays produced by radioactivity, to material deposited in deep-sea ocean crusts and to the inferred composition of the first solids that have formed in the Solar System. We show that considering measurements of the isotopic ratio of 26Al to 60Fe eliminate some of the unknowns when interpreting astronomical results, and discuss the lessons learned from these two isotopes on cosmic chemical evolution.

The discrepancy between observations from γ-ray astronomy of the ^{60}Fe/^{26}Al γ-ray flux ratio and recent calculations is an unresolved puzzle in nuclear astrophysics. The stellar β-decay rate of ^{59}Fe is one of the major nuclear uncertainties impeding us from a precise prediction. The important Gamow-Teller strengths from the low-lying states in ^{59}Fe to the ^{59}Co ground state are measured for the first time using the exclusive measurement of the ^{59}Co(t,^{3}He+γ)^{59}Fe charge-exchange reaction. The new stellar decay rate of ^{59}Fe is a factor of 3.5±1.1 larger than the currently adopted rate at T=1.2  GK. Stellar evolution calculations show that the ^{60}Fe production yield of an 18 solar mass star is decreased significantly by 40% when using the new rate. Our result eliminates one of the major nuclear uncertainties in the predicted yield of ^{60}Fe and alleviates the existing discrepancy of the ^{60}Fe/^{26}Al ratio.

We have calculated the stellar β -decay rate of the important s -process branching point 134 Cs based on the state-of-the-art shell model calculations. At typical s -process temperatures ( T ∼ 0.2–0.3 GK), our new rate is one order of magnitude lower than the widely used rate from Takahashi and Yokoi (hereafter TY87). The impact on the nucleosynthesis in AGB stars is investigated with various masses and metallicities. Our new decay rate leads to an overall decrease in the 134 Ba/ 136 Ba ratio, and well explains the measured ratio in meteorites without introducing the i- process. We also derive the elapsed time from the last AGB nucleosynthetic event that polluted the early solar system to be >28 Myr based on the 135 Cs/ 133 Cs ratio, which is consistent with the elapsed times derived from 107 Pd and 182 Hf. The s -process abundance sum of 135 Ba and 135 Cs is found to increase, resulting in a smaller r -process contribution of 135 Ba in the solar system.

Heavy-ion fusion reactions, such as 12C+12C, play crucial roles in stellar evolution and nucleosynthesis in massive stars. However, limited by the low cross section and large background, it is very challenging to study the reactions at stellar energies. We have developed a 1024-channel prototype TPC named MATE (Multi-purpose time projection chamber for nuclear AsTrophysical and Exotic beam experiments) to study these reactions at stellar energies. The design of our prototype TPC and its performance are described, and the preliminary results of a commissioning experiment for measuring the 12C(12C, α0)20Ne reaction at Ecm = 3.0 MeV are presented. Perspectives of future experiments for the 12C+12C fusion cross section measurement are also provided.

核天体物理是原子核物理与天体物理融合形成的前沿交叉学科,主要目标是研究天体环境中的核过程,进而理解宇宙中化学元素的起源、星体演化和爆发性天体事件。本项目基于兰州重离子加速器研究装置（HIRFL）,发展先进的实验技术和方法,结合国内外其他装置,针对以上核过程,精确测量关键核素的质量、衰变寿命和反应率,确定热碳氮氧循环（HCNO）突破、快质子俘获（rp）、中微子—质子（νp）、中子俘获等过程的核反应路径,理解宇宙中星体能量产生和元素起源。

The 12C+12C fusion reaction plays a crucial role in stellar evolution and explosions. Its main open reaction channels include , 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 and channels can be obtained by summing the S* factors of their corresponding ground-state transitions and the characteristic rays, 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 theS* 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.

发生在中子星壳层内的丰中子熔合反应对中子星演化以及X射线超级爆等现象均会产生影响.受限于放射性束流强度和反应机制的复杂性,实验数据极其缺乏,难以有效约束理论模型.基于活性靶技术的时间投影室(Time Projection Chamber,TPC)将工作气体作为反应靶,具备近4π立体角接受度和三维径迹重建能力,能够实现对反应事件的全记录,显著提高了探测效率,大幅降低了熔合反应截面测量对束流强度的要求.我们研制了240路信号读出的TPC,并使用放射性束流16N对探测器进行了测试,探索了该实验方法的可行性和有效性.为了得到更加精确的反应产物径迹,对反应事件做出更好的筛选,进一步发展了1024路信号读出TPC,并开展了12C+12C库仑位垒附近熔合反应截面测量实验,初步实验结果与已有实验数据符合较好.

AbstractUnderground Nuclear Astrophysics in China (JUNA) will take the advantage of the ultra-low background in Jinping underground lab. High current accelerator with an ECR source and detectors were commissioned. JUNA plans to study directly a number of nuclear reactions important to hydrostatic stellar evolution at their relevant stellar energies. At the first period, JUNA aims at the direct measurements of 25Mg(p,γ)26 Al, 19F(p,α) 16 O, 13C(α, n) 16O and 12C(α,γ) 16O near the Gamow window. The current progress of JUNA will be given.

宇宙中绝大部分锂以及所有比锂重的元素都是通过星体内部核过程产生.文章简要介绍这些核合成过程及其发生的天体物理场所以及重元素起源,深地核天体物理实验等相关前沿研究.

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