We investigate the sensitivity of calcium production to nuclear reaction rates of a 40 solar-mass Population III star using 1D multi-zone stellar models. A comprehensive nuclear reaction network was constructed, and all (p,γ) and (p,α) reaction rates were individually varied by a factor of 10 up and down, identifying 13 preliminary key reactions for calcium production. To propagate the reaction rate uncertainties on calcium production, two sets of Monte Carlo simulations were performed for these key reactions: one adopting STARLIB reaction rates and the other incorporating updated rates from recent experimental data and evaluations. Our results show that Monte Carlo simulations using the updated rates show good agreement with the observed calcium abundance of the extremely iron-poor star SMSS J031300.36-670839.3 within the 68 Additionally, comparisons between 20 solar-mass and 40 solar-mass Population III stellar models confirm that the latter, with updated reaction rates, is more capable of reproducing the observed Ca abundance and [Ca/Mg] ratio.

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.

Nuclear reaction rate databases serve as essential inputs for nucleosynthesis and stellar evolution modeling, directly influencing the accuracy and physical reliability of calculations in various nuclear astrophysics processes. This work comprehensively reviews the major reaction rate databases i.e. REACLIB, STARLIB, and BRUSLIB, highlighting their objectives, data structures, and representative applications, and discussing their coverage, fitting methods, and uncertainty evaluation. These databases have been instrumental in advancing the standardization of nuclear reaction network calculations. However, although these databases have significantly lowered the barrier to performing network modeling, there remains substantial room for improvement in aspects such as database unit structures, update mechanisms, and organizational frameworks. For example, detailed information on the underlying nuclear physics experiments or data analyses is often not included in REACLIB. Therefore, enhancing the stored metadata deserveds careful consideration, as it can significantly improve the reliability of astrophysical modeling. At the same time, the advancement of nuclear astrophysics reaction rate databases depends heavily on continuous progress at the experimental frontier. In recent years, innovative experimental techniques, such as novel 4p high-resolution detector arrays and gamma-charged particle coincidence measurements, have been widely applied to studies of key nuclear astrophysics reactions, significantly expanding research capabilities. To meet the demands of cutting-edge astrophysical studies for accurate reaction rates, the real-time updating and systematic evaluation of experimental data for key reactions present both an important opportunity and an urgent challenge for the development of modern databases. Several important achievements of the JUNA Collaboration at the Jinping underground nuclear astrophysics facility are also presented in this paper, where low-background experiments are conducted. Compared with traditional extrapolations used in databases, these new low-energy measurements are found to provide more direct constraints on key reactions in nuclear astrophysics and crucial experimental support for continuously optimizing databases in the future.

Windowless gas targets avoid the beam-energy loss and straggling introduced by entrance foils and are therefore well suited for direct measurements of low-energy nuclear reactions. A windowless gas-target system designed for operation with milliampere beams has been developed for the Jinping Underground Nuclear Astrophysics facility (JUNA). The system combines three-stage differential pumping, closed-loop gas recovery and purification, a constant-temperature power-compensation calorimeter, and a position-resolved target-thickness monitor based on secondary elastic scattering. Stable operation was achieved over a target-pressure range of 1-3 mbar, with pressure fluctuations below 1

The 26Mg(p, γ)27Al reaction, as part of the Mg-Al cycle, is closely related to the abundance ratio of 26Al to 27Al in stars. It also has a direct connection to the Mg-Al anti-correlation observed in globular clusters (GCs). Its reaction rate is determined by multiple known and unknown low-energy resonances. In this work, we measured the angular distributions of the proton transfer reaction 26Mg(7Li, 6He)27Al populating three levels at excitation energies from 8.324 MeV to 8.597 MeV using the HI-13 tandem accelerator and a high-precision magnetic spectrograph. Proton spectroscopic factors were extracted from the angular distributions corresponding to three states, and the resonance strengths which make contributions to the reaction rate were updated. At the same time, the latest calculated reaction rate shows the result for the 52.8 keV resonance significantly increases the total reaction rate at T9 < 0.03.

Based on the ultra-low background environment of China Jinping Underground Laboratory (CJPL), the JinPing Underground Nuclear Astrophysics (JUNA) Collaboration has been established to directly measure some crucial nuclear reactions at Gamow windows in hydrostatic burning processes of stars. This article covers the technological breakthroughs, current experimental results, and the status and future plans of JUNA project. These efforts provide valuable insights for understanding the key mechanisms of stellar evolution and nucleosynthesis.

Present and future rare isotope accelerator facilities provide new opportunities to explore the structure of unstable nuclei. We report the measurements of the elastic scattering angular distributions of 21Na and 22Na on the doubly magic 40Ca above the Coulomb barrier energies, using high-purity post-accelerated ISOL beams from Beijing Radioactive Ion Beam Facility (BRIF). Angular distributions were measured with a silicon detector telescope array, and relative cross sections were determined with a CaF2 target on Au backing. The data were well reproduced by optical model calculations with Woods–Saxon and USNP potentials, the latter giving better agreement. These results confirm the stable operation and performance of the BRIF ISOL production and post-acceleration system, demonstrate its capability to provide radioactive beams of useful intensity and purity for future investigations of reaction dynamics and astrophysically relevant processes involving proton-rich nuclei, and simultaneously extend proton-rich elastic scattering studies to heavier systems.

Type I X-ray bursts are thermonuclear flashes on the surface of accreting neutron stars, involving hundreds of nuclei and thousands of reactions with larger uncertainties in reaction rates. To investigate the impact of nuclear reaction rate uncertainties on type I X-ray burst nucleosynthesis, comprehensive Monte Carlo simulations were performed with temperature-independent and -dependent variations in reaction rates using the REACLIB and STARLIB libraries, respectively. A total of 1711 (p, gamma), (p, alpha), (alpha, p), and (alpha, gamma) reaction rates are varied simultaneously along with their inverse reactions via detailed balance. For the first time, it has been found that Monte Carlo sampling with larger perturbations to these reaction rates may lead to multipeak abundance distributions for certain isotopes, such as 64Zn and 55Co. These multipeak structures arise not only from coupled reactions but also from single reactions in some cases. Our studies also confirm previously identified key reactions and provide more robust lists that deserve priority consideration in future studies.

Measuring cross sections of nuclear reactions,such as the so-called"Holy Grail"reaction,12C(α,γ)16O,is essential for understanding stellar nucleosynthesis but presents significant challenges due to extremely low cross sections.Key challenges include significant energy loss as ions penetrate the target material,limiting measurements to thin target layers.To overcome these obstacles,we propose a novel method,the in-target energy loss compensating(eLOC)method,specifically designed for gas targets,which utilizes a gas-filled magnetic field and accelerating electric fields to compensate for ion energy loss in the target.Simulations show that this approach significantly enhances the effective target thickness by over 140 times in the case of the"Holy Grail"reaction with an inverse-kinematics setup.This eLOC method may provide a powerful new tool for obtaining critical data in nuclear astrophysics,thereby advancing our understanding of stellar nucleosynthesis and the origins of elements in the universe,as well as benefiting other related fields such as isotope production.

20Na is a well-known β-delayed α emitter, owing to the large decay energy of 20Na above the α + 16O threshold in the A=5α daughter nucleus 20Ne. In this work, the decay property of 20Na is investigated in detail via the β-γ β-α and β-γ-α coincidence spectroscopy. As the day-one experiment of the Beijing Rare Isotope Facility (BRIF), the intense 20Na beam was produced using the Isotope Separator On Line (ISOL) technique through the 100 MeV proton bombarding a stack of MgO as a thick target. Specific interest was focused on the exotic decay mode of 20Na; the previously reported low-energy α lines at 713 and 846 keV were confirmed, and several weak β-γ-α decay sequences were clearly identified for the first time, thanks to the strong resolving power of α-γ coincidence spectroscopy. The decay properties of 20Na are compared to the shell model calculation, which agree reasonably well with the allowed β transition strengths and subsequent electro-magnetic transitions with the use of the sd shell-model space with the USDB interaction.

In modern nuclear physics experiments, identifying events of interest remains challenging in nuclear reaction studies using active-target time projection chambers (TPCs). In this work, machine learning techniques are employed to analyze complex event images from the ^12C+^12C fusion reaction recorded with multi-purpose active-target time projection chamber for nuclear experiments (MATE). Specifically, we successfully applied residual neural network (ResNet-50, ResNet-34, and ResNet-18) and a Visual Geometry Group network (VGG-19) to classify elastic scattering and fusion reaction events from the ^12C+^12C reaction. The classification results of the four models are nearly identical, with accuracies of approximately 97% for the simulated data and about 90% for the experimental data when benchmarked against labels assigned by the conventional analysis. Moreover, the models recover a subset of events that were mislabeled by the conventional analysis. These models are also applied to classify events from different fusion reaction channels, with classification accuracies of approximately 95% on the simulated data. In addition, a Convolutional Neural Network (CNN) model is developed to reconstruct the reaction vertex, providing a complementary approach for vertex reconstruction. These results indicate that machine learning techniques can effectively classify events from different reaction channels and can reconstruct the reaction vertex with useful accuracy, thereby supporting future analyses of complex nuclear reaction data.

The Jinping Underground experiment for Nuclear Astrophysics (JUNA) takes advantage of the ultra-low background of the CJPL to conduct experiments for directly studying crucial reactions at stellar energies in the evolution of stars. In 2020, JUNA commissioned a mA level high current accelerator based on an ECR source, as well as high efficiency BGO and He-3 detectors. Direct measurements of key nuclear reactions, including Mg-25(p,gamma)Al-26, F-19(p, alpha gamma)O-16, F-19(p,gamma)Ne-20, C-12(alpha, y)O-16 and O-18(alpha, y)Ne-22, were performed in JUNA with improved precision and closer to the Gamow window relative to previous measurements. These precise reaction rates provide valuable insights into the high precision astrophysics simulation.

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.

We present a novel experiment to investigate the spectroscopic factor (SF) of the C-15 ground state for the first time using single-neutron removal transfer reactions on C-15. Two consistent SFs were derived from the (p, d) and (d, t) reactions, which were subsequently used to deduce the C-14(n, gamma)C-15 reaction cross section and the corresponding stellar reaction rate. A typical cross section of 3.89 +/- 0.76 mu b is determined at E-c.m. = 23.3 keV. At the temperature range of 0.01-4 GK, our new reaction rate is 2.4-3.7 times higher than that of the first direct measurement and 20%-25% lower than that of the most recent direct measurement. Moreover, it is interesting that we can associate a long-standing nuclear structure issue, i.e., the so-called "quenching" effect, with this astrophysically relevant reaction. Finally, motivated by astrophysical interests of this reaction decades ago, implications of our new rate for several astrophysical problems are evaluated using state-of-the-art theoretical models. Our calculations demonstrate that the abundances of N-14 and N-15 can be enhanced in the inner regions of asymptotic giant branch stars, though with minimal impact on the chemical compositions of the interstellar medium. In the inhomogeneous Big Bang nucleosynthesis, the updated reaction rate can lead to a similar to 20% variation in the final yields of( 15)N in neutron-rich regions. For the r-process in the core-collapse supernovae, a slight difference of similar to 0.2% in the final abundances of heavy elements with A > 90 can be found by using our new rate.

Directly measuring key nuclear reactions within the Gamow window of stars is a critical frontier in modern nuclear astrophysics. The China Jinping Underground Laboratory (CJPL) offers an ultra-low-background environment, serving as the foundation for the China Jinping deep Underground Nuclear Astrophysics experimental platform (JUNA). By utilizing JUNA's high-intensity accelerator, efficient detectors, and advanced targets, several crucial nuclear reactions relevant to stellar evolution have been successfully measured within the energy ranges of relevant stars. These reactions include Mg-25(p,gamma)Al-26, F-19(p, alpha)O-16, C-13(alpha, n)O-16, and C-12(alpha, gamma)O-16, significantly enhancing our understanding of heavy element production in early and massive stars. The JUNA experiment has achieved internationally advanced levels in data statistics, measurement precision, and sensitivity. This article will summarize JUNA's key experimental results and compare them with current international advancements to highlight the platform's unique strengths. Additionally, it will offer an outlook on the future development of JUNA Run-2.

A promising experiment is proposed, which aims to resolve the long-standing solar metallicity puzzle by reducing the uncertainty from microscopic nuclear reactions at the deepest underground laboratory.

Isoscalar dipole transitions are a distinctive fingerprint of cluster structures. A 1^{-} resonance at 7.27(10) MeV, located just below the α-emission threshold, has been observed in the deuteron inelastic scattering reactions off ^{10}Be. The deformation lengths of the excited states in ^{10}Be below 9 MeV have been inferred from the differential cross sections using coupled channel calculations. This observed 1^{-} resonance has isoscalar characteristics and exhausts approximately 5%-15% of the isoscalar dipole energy-weighted sum rule, providing evidence for pronounced α cluster structure in ^{10}Be. The Gamow coupled channel approach supports this interpretation and suggests the near-threshold effect might be playing an important role in this excitation energy domain. The α+α+n+n four-body calculation reproduces the observed enhanced dipole strength, implying that the four-body cluster structure is essential to describe the 1^{-} states in ^{10}Be.

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.