The -delayed neutron emission probability ( P_n ) is a key observable for characterizing the decay strength of very neutron-rich nuclei and the rapid neutron capture process in nuclear astrophysics. A Long Helium-3 Neutron Array (LHENA) has been developed at the Beijing Rare Isotope Facility (BRIF) to enable P_n measurements using Isotope Separator On Line (ISOL) pulsed beams. LHENA is designed to work in conjunction with a tape driver and auxiliary detectors, so that particles, -delayed neutrons and γ rays emitted from the implanted nuclei can be measured simultaneously in cyclic mode. LHENA consists of 21 long ^3 He proportional counters embedded in a polyethylene moderator with a two-ring configuration, which provides a flat neutron detection efficiency up to 3 MeV according to our Geant4 simulations. The detection efficiency has been experimentally determined to be 16.4( ± 0.4 ) ^51 V(p,n) ^51 Cr reaction for neutron energies in the 120–700 keV range. A good efficiency flatness and a very low background have been verified for LHENA, laying a solid foundation for the first P_n measurement using very neutron-rich Rb isotopes at BRIF.

The 14N(p,1)15O reaction plays a crucial role in studies of hydrogen burning. Irradiation-resistant nitride targets are essential for extending direct measurements of this reaction to lower energies. In this work, we fabricated nitride targets using filter cathodic vacuum arc (FCVA) and low-pressure chemical vapor deposition (LPCVD) techniques. The thickness and chemical composition of the targets, as well as the impurity levels of the TiN targets, were evaluated through corresponding reaction measurements. The results indicate that FCVAfabricated TiN targets exhibit the best comprehensive performance. The deterioration of the TiN targets under the bombardment of a similar to 2 mA proton beam was investigated by monitoring the yield curves. The reduction rates of the atomic areal density for these targets were found to be in the range of 0.084-0.16%/C. The prepared TiN targets successfully advanced the measurement of 14N(p,1)15O reaction to Ep = 110 keV in a ground laboratory, which will enable further extension to Ep = 70 keV at the Jinping Underground Nuclear Astrophysics facility (JUNA) in the future.

The Beijing Radioactive Ion-beam Facility (BRIF), based on the Isotope Separation On-Line (ISOL) technique, consists of a 100 MeV proton cyclotron as the driving accelerator, a two-stage ISOL system for ion separation, a 13-MV tandem accelerator for post-acceleration, a superconducting linac for further boosting beam energies. It is capable of providing ISOL beams in the energy range from 60 to 300 keV, and post-accelerated beams in the energy range from 3 to 10 MeV/u for nuclei with mass numbers of A < 80. For nuclei with A up to 170, energies are still able to reach 3 MeV/u. This facility offers opportunities to address key questions of current interest in nuclear astrophysics, nuclear structure and reactions of unstable nuclei. In this review we present a comprehensive introduction to the BRIF and the typical experimental instruments installed on it, and then summarize current experimental results on unstable Na and Rb isotopes and future plan for development of the BRIF to improve its performance.

Background: The primary goal of studying isospin dynamics via heavy-ion reactions is to explore the isospin dependence of effective interactions within the nuclear equation of state (EOS). Purpose: This work aims to investigate the effects of nuclear incompressibility (K0) on neutron-proton equilibration in projectile-like fragments (PLFs). Method: We simulate 70Zn + 70Zn collisions at 35 MeV/nucleon using the isospin-dependent quantum molecular dynamics (IQMD) model, coupled with the statistical decay code GEMINI. Results: The IQMD calculations not only reproduce experimental data patterns but also reveal the dynamic mechanisms underlying the binary breakup of PLFs. The rotation of PLFs is influenced by the transformation of angular momentum, which is connected to the isoscalar component of the nuclear EOS. This connection explains why shifts in K0 affect the description of neutron-proton equilibration as measured by PLF rotation. The calculations demonstrate that a model with a smaller K0 paired with a softer symmetry energy, or a larger K0 with a slightly stiffer symmetry energy, both offer better indications of neutron-proton equilibration. Conclusion: Considering the uncertainty in K0, the slope of the symmetry energy is constrained to L = 30 +/- 10 MeV, providing valuable insights into the nuclear EOS.

The C-12+C-12 fusion reaction at deep subbarrier energies is important for understanding the carbon burning process in massive star and explosive binary systems. However, its reaction rates are very difficult to measure directly or evaluate by simple extrapolation due to the extremely small cross sections and complex resonance structures near the Gamow window. In this work, we use one of its exit channels, i.e. Na-23 + p to populate the excited states of the compound nucleus Mg-24 via the conventional thick-target inverse kinematics method. By applying gamma-charged particle coincidence, we have obtained excitation functions for the proton and a emission channels, respectively, and derived the resonance parameters through a simultaneous multi-channel R-matrix analysis. It is clear that a series of discrete resonances exist in the most relevant excitation energy region of Mg-24. The astrophysical S-factor of the C-12+C-12 fusion reaction is evaluated by adopting a systematic reduced width for the entrance channel. In particular, branching ratios of the dominant four decay channels are estimated across the entire Gamow window of the C-12+C-12 fusion reactions. Significant fluctuations are shown that may have strong impacts on the final outcome of the carbon burning process.

A low-background γ spectrometer named the Gamma spectrometer for Nuclear Activation Studies (GNAS) was developed to detect scarce γ radioactivity, with a special focus on conducting activation experiments in nuclear astrophysics. It consisted of a well-type HPGe detector surrounded by optimized multi-layer shielding, which reduced the laboratory background counting rate by 99.5 γ line of ^7Be . The near 4π geometry of the HPGe detector introduces a severe true coincidence summing (TCS) effect along with its high detection efficiency. To determine the intrinsic detection efficiency and correct for the TCS effect, a Monte Carlo simulation method was developed with the Geant4 toolkit. The detector model was optimized by matching the simulated full energy peak (FEP) statistics with those of a ^137Cs monoenergetic source and calibrated ^55,57,58Co sources produced by low-energy proton beam bombardment of natural iron. The intrinsic detection efficiency curve was obtained, and an algorithm for the correction of the TCS effect was programmed using decay data from the ENSDF library and Nuclear Wallet Cards. The GNAS fulfills the requirements of the ongoing activation measurement of proton- and alpha-induced reactions in nuclear astrophysics on the ground and at the Jinping Underground Nuclear Astrophysics (JUNA) facility.

The solar composition problem has puzzled astrophysicists for more than 20 years. Recent measurements of carbon-nitrogen-oxygen (CNO) neutrinos by the Borexino experiment show a ∼2σ tension with the "low-metallicity" determinations. ^{14}N(p,γ)^{15}O, the slowest reaction in the CNO cycle, plays a crucial role in the standard solar model (SSM) calculations of CNO neutrino fluxes. Here we report a direct measurement of the ^{14}N(p,γ)^{15}O reaction, in which S-factors for all transitions were simultaneously determined in the energy range of E_{p}=110-260  keV for the first time. Our results resolve previous discrepancies in the ground-state transition, yielding a zero-energy S-factor S_{114}(0)=1.93±0.10  keV b, which is 15% higher than the 1.68±0.14  keV b recommended in Solar Fusion III (SF-III). With our S_{114} values, the SSM B23-MB22p, and the latest global analysis of solar neutrino measurements, the C and N photospheric abundance determined by the Borexino experiment is updated to N_{CN}=(4.42_{-0.63}^{+0.70})×10^{-4}. This new N_{CN} value agrees well with latest "high-metallicity" composition; however, it is also consistent with the "low-metallicity" determination within ∼1σ CL, indicating that the solar metallicity problem remains an open question. In addition, the significant reduction in the uncertainty of S_{114} paves the way for the precise determination of the CN abundance in future large-volume solar neutrino measurements.

The C-12 (alpha,gamma)O-16 reaction plays a pivotal role in nuclear astrophysics research. The direct measurement of this reaction remains particularly challenging due to its extremely low cross section (approximately 10-17 barn at 300 keV) within the Gamow window. This study addresses the critical need for irradiation-resistant C-12-enriched targets to enable accurate measurements. We successfully fabricated a C-12-enriched diamond target on molybdenum substrate through Microwave Plasma Chemical Vapor Deposition (MPCVD), demonstrating remarkable stability under high-intensity proton beam irradiation. Experimental results revealed only a 1.8% decrease in the C-12 (p,gamma)N-13 reaction yield in the C-12 layer following proton bombardment at 270 keV with 2 mA beam current and a total accumulated charge of 124.2 C, indicating a significant improvement compared to conventional carbon targets. Isotopic analysis confirmed a C-13/C-12 ratio of (9.7 +/- 1.3)x10-5, verifying the absence of contamination during MPCVD processing. Additionally, we developed a novel nuclear-reaction-based methodology for quantifying hydrogen content in thin films, establishing an upper limit of 0.058% (95% confidence level) for hydrogen concentration in the diamond target. The combined irradiation resistance and isotopic purity of this target meet the stringent requirements for direct C-12 (alpha,gamma)O-16 reaction measurements in astrophysical environments.

The precise determination of cross sections for key nuclear reactions within the Gamow window is crucial for advancing the study of stellar evolution and nucleosynthesis. However, extremely low reaction yields combined with the cosmic-ray-induced background make these measurements highly challenging, particularly for capture reactions. This work demonstrates the second configuration of the large-scale modular BGO detection array (LAMBDA-II) designed to capture reaction measurements and introduces a method for suppressing γ -ray detection background in ground laboratories. By employing active and passive shielding, the background of LAMBDA-II was significantly reduced by approximately two orders of magnitude, reaching 8.1×10^-3 and 1.0×10^-3 keV^-1h^-1 in the 6–11 and 11–20 MeV energy ranges, respectively. When combined with a mA-scale intensity beam, this reduced background enables the investigation of several capture reactions of astrophysical interest in ground laboratories.

To investigate the impact of nuclear reaction rate uncertainties on type I X-ray burst nucleosynthesis, comprehensive Monte Carlo simulations are performed with temperature-independent and -dependent variations in reaction rates using the REACLIB and STARLIB libraries, respectively. A total of 1,711 (p, γ), (p, α), (α, p), and (α, γ) reactions are varied simultaneously, along with their inverse reactions, via detailed balance. For the first time, it is found that Monte Carlo sampling with larger perturbations to these reaction rates may lead to multi-peaked abundance distributions for some isotopes. These multi-peak structures arise not only from coupled reactions but also, in some cases, from single reactions. Our study also confirmed previously identified key reactions and provides more robust lists. These reactions deserve priority consideration in future study.

Nuclear astrophysics is a rapidly developing interdisciplinary field of research that has received extensive attention from the scientific community since the mid-twentieth century. Broadly, it uses the laws of extremely small atomic nuclei to explain the evolution of the universe. Owing to the complexity of nucleosynthesis processes and our limited understanding of nuclear physics in astrophysical environments, several critical astrophysical problems remain unsolved. To achieve a better understanding of astrophysics, it is necessary to measure the cross sections of key nuclear reactions with the precision required by astrophysical models. Direct measurement of nuclear reaction cross sections is an important method of investigating how nuclear reactions influence stellar evolution. Given the challenges involved in measuring the extremely low cross sections of nuclear reactions in the Gamow peak and preparing radioactive targets, indirect methods, such as the transfer reaction, coulomb dissociation, and surrogate ratio methods, have been developed over the past several decades. These are powerful tools in the investigation of, for example, neutron-capture (n, γ ) reactions with short-lived radioactive isotopes. However, direct measurement is still preferable, such as in the case of reactions involving light and stable nuclei. As an essential part of stellar evolution, these low-energy stable nuclear reactions have been of particular interest in recent years. To overcome the difficulties in measurements near or deeply within the Gamow window, the combination of an underground laboratory and high-exposure accelerator/detector complex is currently the optimal solution. Therefore, underground experiments have emerged as a new and promising direction of research. In addition, to better simulate the stellar environment in the laboratory, research on nuclear physics under laser-driven plasma conditions has gradually become a frontier hotspot. In recent years, the CIAE team conducted a series of distinctive nuclear astrophysics studies, relying on the Jinping Underground Nuclear Astrophysics platform and accelerators in Earth’s surface laboratories, including the Beijing Radioactive Ion beam Facility, as well as other scientific platforms at home and abroad. This research covered nuclear theories, numerical models, direct measurements, indirect measurements, and other novel approaches, achieving great interdisciplinary research results, with high-level academic publications and significant international impacts. This article reviews the above research and predicts future developments.

The $^{12}\mathrm{C}(\ensuremath{\alpha},\ensuremath{\gamma})^{16}\mathrm{O}$ reaction substantially influences the abundance ratios of the main isotopes of carbon and oxygen and hence has been regarded as the holy grail in nuclear astrophysics. Its importance lies in the fact that it significantly affects the yield of key elements and that it plays a crucial role in the study of the mass gap of black holes. This reaction's cross section is greatly influenced by the subthreshold state 7.117-MeV ${1}^{\ensuremath{-}}$ of $^{16}\mathrm{O}$, which is challenging to determine. To study such states the $\ensuremath{\alpha}$-cluster transfer reaction can be helpful. In this work, the angular distribution of the $^{12}\mathrm{C}(^{11}\mathrm{B},^{7}\mathrm{Li})^{16}\mathrm{O}$ reaction was measured, leading to the 7.117-MeV ${1}^{\ensuremath{-}}$ state at ${E}_{^{11}\mathrm{B}}(\mathrm{lab})=50$ MeV. By using the finite-range distorted-wave Born approximation and coupled-reaction-channel analysis, we obtained the asymptotic normalization coefficient (ANC) to be $(2.54\ifmmode\pm\else\textpm\fi{}0.40)\ifmmode\times\else\texttimes\fi{}{10}^{28}$ ${\mathrm{fm}}^{\ensuremath{-}1}$ and the reduced $\ensuremath{\alpha}$ width to be $4.92\ifmmode\pm\else\textpm\fi{}0.77$ keV at a channel radius of 6.5 fm. Then, by using the $R$-matrix code azure, we calculated the astrophysical $S$ factor of the $^{12}\mathrm{C}(\ensuremath{\alpha},\ensuremath{\gamma})^{16}\mathrm{O}$ reaction and found that the astrophysical ${S}_{E1}$ (300) factor of the ground-state transitions is $55.3\ifmmode\pm\else\textpm\fi{}9.0$ keV b. This value is lower than what was found in previous works, indicating that the $S$ factor is highly sensitive to the ANC.

The ^12C+ ^12C fusion is one of the most important reactions in modern nuclear astrophysics. The trend and magnitude of the reaction rate within the Gamow window strongly influence various astrophysical processes. However, direct measurement of this reaction is extremely difficult, which makes it necessary to develop indirect methods. In this study, the ^23Na+p reaction system was used to study the compound nucleus ^24Mg . We employed a thick-target inverse kinematics method combined with the γ -charged-particle coincidence technique to measure the proton and α exit channels of ^24Mg . Technical details of the ^23Na+p thick-target inverse kinematics experiment and analysis are presented herein.

Calcium production and the stellar evolution of first-generation stars remain fascinating mysteries in astrophysics. As one possible nucleosynthesis scenario, break-out from the hot carbon–nitrogen–oxygen (HCNO) cycle was thought to be the source of the calcium observed in these oldest stars. However, according to the stellar modeling, a nearly tenfold increase in the thermonuclear rate ratio of the break-out ^19 F(p, γ ) ^20 Ne reaction with respect to the competing ^19 F(p, α ) ^16 O back-processing reaction is required to reproduce the observed calcium abundance. We performed a direct measurement of this break-out reaction at the China Jinping underground laboratory. The measurement was performed down to the low-energy limit of E_c.m. = 186 keV in the center-of-mass frame. The key resonance was observed at 225.2 keV for the first time. At a temperature of approximately 0.1 GK, this new resonance enhanced the thermonuclear ^19 F(p, γ ) ^20 Ne rate by up to a factor of ≈ 7.4, compared with the previously recommended NACRE rate. This is of particular interest to the study of the evolution of the first stars and implies a stronger breakdown in their “warm” CNO cycle through the ^19 F(p, γ ) ^20 Ne reaction than previously envisioned. This break-out resulted in the production of the calcium observed in the oldest stars, enhancing our understanding of the evolution of the first stars.

In thermonuclear reactions of nuclear astrophysical interest,some can produce short-lived products that emit positrons.These positrons will annihilate with electrons in the target and then produce a pair of 511 keV γ-rays,which can be used to determine the reaction yield and calculate the cross-section as well as the astrophysical S-factor.Recently,an in situ measurement method for positron annihilation on experimental terminals has been proposed.This method takes advantage of the characteristic opposite direction of the 511 keV γ-ray pairs and uses the opposite units in the detection array for spatial co-incidence measurements to suppress background.In this study,we investigated this method using the newly developed large modular BGO detector array LAMBDA-Ⅱ.The results show that the detection efficiency of LAMBDA-Ⅱ for in situ β+decay of reaction products is(7.6±0.2)％,which is in good agreement with the value given by Monte Carlo simulations.The yield of the 14N(p,γ)15O 259 keV resonance determined by in situ measurement agrees well with that derived from prompt γ-ray meas-urement,verifying the reliability of this method and providing a solid foundation for its further application in nuclear astro-physics research.

22Na(p,γ)23Mg and 19Ne(α,p)22Na are two crucial reactions in the so-called NeNa-MgAl cycle and the rapid-pro-ton process,their astrophysical reaction rates are indispensable inputs in understanding the outburst mechanism and element synthesis of novae.Since many proton resonance levels in odd-A compound nucleus 23Mg may be involved at nova temperat-ure,existing measurements can only provide partial effective information on the 22Na(p,γ)23Mg reaction,large discrepancies still exist in the astrophysical reaction rates of the two reactions.In the present work,22Na+p resonance scattering via thick target inverse kinematics was studied at RIBLL1 radioactive beam line in the HIRFL national laboratory at Lanzhou.Excita-tion functions of 22Na(p,p)are obtained in the energy range of Ec.m.=1.5 to 4 MeV.Obvious resonance structure is observed in the 23Mg compound nucleus,resonance parameters are deduced for 22 proton resonance states in 23Mg via R-matrix analys-is,which will be used for the evaluation of the astrophysical reaction rates of 22Na(p,γ)23Mg and 19Ne(α,p)22Na.

The 12C(alpha, gamma )16O reaction substantially influences the abundance ratios of the main isotopes of carbon and oxygen and hence has been regarded as the holy grail in nuclear astrophysics. Its importance lies in the fact that it significantly affects the yield of key elements and that it plays a crucial role in the study of the mass gap of black holes. This reaction's cross section is greatly influenced by the subthreshold state 7.117-MeV 1- of 16O, which is challenging to determine. To study such states the alpha-cluster transfer reaction can be helpful. In this work, the angular distribution of the 12C(11B, 7Li)16O reaction was measured, leading to the 7.117-MeV 1- state at E11B(lab) = 50 MeV. By using the finite-range distorted-wave Born approximation and coupled-reaction-channel analysis, we obtained the asymptotic normalization coefficient (ANC) to be (2.54 +/- 0.40) x 1028 fm-1 and the reduced alpha width to be 4.92 +/- 0.77 keV at a channel radius of 6.5 fm. Then, by using the R-matrix code AZURE, we calculated the astrophysical S factor of the 12C(alpha, gamma )16O reaction and found that the astrophysical SE1 (300) factor of the ground-state transitions is 55.3 +/- 9.0 keV b. This value is lower than what was found in previous works, indicating that the S factor is highly sensitive to the ANC.

Total absorption gamma-ray spectroscopy (TAGS) is a powerful tool for measuring complex γ transitions, which has been effectively applied to the study of reactor decay heat. This paper presents the design of a new TAGS detector, the large-scale modular BGO detection array (LAMBDA), tailored for measuring β -decay intensity distributions of fission products. The modular design allows the LAMBDA detectors to be assembled in various configurations. The final version of LAMBDA consists of 102 identical 60 mm × 60 mm × 120 mm BGO crystals and exhibits a high full-energy peak efficiency exceeding 80 ∼ 8 MeV based on a Monte Carlo simulation. Currently, approximately half of the LAMBDA modules have been manufactured. Tests using γ -ray sources and nuclear reactions demonstrated favorable energy resolution, energy linearity, and efficiency uniformity across the modules. Forty-eight modules have been integrated into the prototype LAMBDA-I. The capability of LAMBDA-I in β -delayed γ -decay experiments was evaluated by commissioning measurements using the ^152 Eu source.

贝塔奥斯陆实验方法为研究高激发态下的放射性核素性质以及探究从铁到铀的元素核合成过程提供了一种重要的研究工具。本文提出了一种新型数据处理技术，旨在消除贝塔衰变电子对贝塔奥斯陆实验中了子核伽马退激衰变探测的影响，从而准确地展开观测到的伽马射线光谱。通过运用伽马射线与衰变电子的综合探测器响应函数矩阵，将列主元消去法与逐步迭代反解法相结合，确定真实的入射伽马光谱。通过模拟和反演计算，证实了所提出方法的可靠性与有效性。

This paper introduces a new platform established for nuclear astrophysics studies on Hefei Facility in China. Currently, the high-voltage accelerator can deliver a proton beam with current up to approximately 5 mA in the energy range of & SIM;50-350 keV. The proton beam energy and its spread were calibrated with two resonant reactions, and satisfy the experimental beam requirements for nuclear astrophysics studies. At the 90 degrees beamline of this platform, we have installed a new setup (including target chamber, cold trap, silicon detectors, preamplifiers and DAQ), which is specifically designed for charged-particle measurements. Based on a careful background study of the target chamber, the charged-particle measurement of the19F(p, ⠋0)16O reaction can be performed down to the low-energy region of astrophysical interest with this setup. Some other astrophysical experiments are also prospected.