Nuclear astrophysics group is focused on nucleosynthesis in stars from the aspect of experiments and theories. Every nucleus, whether in our bodies or in remote stars, may originate from hundreds of stellar evolution or supernova explosion processes. To simulate the nucleosynthesis in stars, we perform the nuclear reactions by using energetic particles provided by accelerators to bombard targets, and then extract the crucial nuclear information by detectors, such as time project chamber. Comparing astronomical observations with our results obtained in the laboratory, we collaborate with astrophysics and astronomers to explore and solve the problem of the origin of elements in the universe.
1. The measurement of important nuclear reactions in stars:
About 50% of the heavy elements in the solar system, from iron to bismuth, are produced by slow neutron capture in the asymptomatic giant, and the 13C(α,n)16O reaction is the main neutron source for this process. For the carbon burning in the evolution of massive stars, the 12C+12C reaction is a key reaction, and it is also the ignition reaction of Type Ia supernovae and X-ray superbursts. The cross-sections of these nuclear reactions are extremely small in the stellar energies. Direct measurements of these cross-sections are long-standing problems in nuclear astrophysics. Based on the high-intensity accelerators together with ultra-low background detection technology, we will pursue the accurate measurements of astrophysically important reactions, such as 13C(α,n)16O and 12C+12C, which provides reliable reaction rates for astrophysical studies.
2. The research of nuclear weak-interaction decay rate in the stellar environment:
The nuclear weak-interaction decay serves as a branching point at the stellar nucleosynthesis route. It could have a great impact on the nucleosynthesis of some important nucleus, e.g., 60Fe, 135Cs. The extreme temperature and density in the stellar environment could make the nuclear weak-interaction decay (β-decay/electron capture) differ from the terrestrial value. However, it is not accessible for the direct measurement at laboratory due to the technical limit. The charge exchange measurement is an essential in-direct method to obtain the stellar weak-interaction decay rate. In cooperation with the Michigan State University team, we have carried out experimental research on charge exchange reaction to accurately determine the stellar decay rate of 59Fe and its impact on the 60Fe nucleosynthesis. It would contribute to the research of near-Earth supernovae, ？-ray astronomy, and other fields.
3. Theoretical research on nucleosynthesis:
One of the eleven great physics questions of the 21st century: How were the heavy elements, from iron to uranium, made? The nucleosynthetic process of these elements involves a number of nuclear ingredients about masses, lifetimes, and fission, etc and various reaction rates of extremely neutron-rich and proton-rich isotopes. The nature of these isotopes determines the abundance of elements produced in astrophysical environments, such as supernovae and neutron star mergers. Existing facilities are not yet able to produce these important nuclei and to study their related properties. We are using theoretical models to predict these nuclear properties, provide the reaction rate database, and identify the experimental objectives for future facilities such as High Intensity heavy ion Accelerator Facility (HIAF), which is being constructed in China.
4. Time Projection Chamber (TPC) for experiments with radioactive ion beams:
Direct measurements of many astrophysical important reactions in the laboratory are very difficult. The main challenges for cross-section measurements in stellar energies are the very low reaction rate, the relatively strong background and limit of available beam intensity. The Time Projection Chamber based on active-target technology could record three dimensional tracks for charged particles, which fully take the advantage of the thick target and beam intensity. These capabilities significantly boost the luminosity of experiments. As a tracking detector, TPC also provides substantial suppression of the background and can be used in the studies of exotic nuclei decay and very rare event detection in experiments. At present, we have designed and built an active-target TPC named MATE-TPC（Multi-purpose Active-target Time-projection-chamber）with 4000-channel readouts. It will be used in a series of nuclear experiments, such as nuclear fusions, transfer reactions, charge-exchange reactions, exotic decay.
(1) “The Stellar β-decay Rate of 134Cs and Its Impact on the Barium Nucleosynthesis in the s-process”, Kuo-Ang Li*, Chong Qi*, Maria Lugaro*, Andrés Yagüe López, Amanda I. Karakas, Jacqueline den Hartogh, Bing-Shui Gao, Xiao-Dong Tang, The Astrophysical Journal Letters 919, L19 (2021).
(2) “New 59Fe Stellar Decay Rate with Implications for the 60Fe Radioactivity in Massive Stars”, B. Gao*, S. Giraud, K. A. Li*, A. Sieverding, R. G. T. Zegers, X. Tang, J. Ash, Y. Ayyad-Limonge,D. Bazin, S. Biswas, B. A. Brown, J. Chen, M. DeNudt, P. Farris, J. M. Gabler, A. Gade, T. Ginter, M. Grinder, A. Heger, C. Hultquist, A. M. Hill, H. Iwasaki, E. Kwan, J. Li, B. Longfellow, C. Maher, F. Ndayisabye, S. Noji, J. Pereira, C. Qi, J. Rebenstock, A. Revel, D. Rhodes, A. Sanchez, J. Schmitt,C. Sumithrarachchi, B. H. Sun, and D. Weisshaar, Phys. Rev. Lett. 126, 152701 (2021).
(3) “Low event rate neutron detector array using the coincidence between plastic scintillator and Helium-3 proportional counters”, H. X. Huang， B. Gao*, Y. T. Li, J. Ren， X C. Ruan, H. Chen, X. D. Tang，N. T. Zhang，T. Y. Jiao，G. Lian, Nucl. Instrum. Methods Phys. Res., Sect. A, 1003, 165323 (2021).
(4) “Studying the heavy-ion fusion reactions at stellar energies using Time Projection Chamber”, Z. C. Zhang, X. Y. Wang, T. L. Pu, C. G. Lu*, N. T. Zhang*, J. L. Zhang, L. M. Duan, B. S. Gao, J. Gao, R. J. Hu, E. Q. Liu, K. A. Li, Q. T. Li, Y. T. Li, B. F. Lv, H. Y. Ma, J. B. Ma, H. J. Ong, Y. Qian, L. H. Ru, L. T. Sun, X. D. Tang, J. Y. Xu, X. D. Xu, Y. Yang, Y. H. Zhai, H. Y. Zhao, H. W. Zhao, Nuclear Inst. and Methods in Physics Research, A1016, 165740 (2021).
(5) “Progress in nuclear astrophysics of east and southeast Asia”, Azni Abdul Aziz, Nor Sofiah Ahmad, S. Ahn, Wako Aoki, Muruthujaya Bhuyan, Ke-Jung Chen, Gang Guo, K. I. Hahn, Toshitaka Kajino*, Hasan Abu Kassim, D. Kim, Shigeru Kubono, Motohiko Kusakabe, A. Li, Haining Li, Z. H. Li, W. P. Liu*, Z. W. Liu, Tohru Motobayashi, Kuo-Chuan Pan, T.-S. Park, Jian-Rong Shi1, Xiaodong Tang* , W. Wang, Liangjian Wen, Meng-Ru Wu, Hong-Liang Yan and Norhasliza Yusof, AAPPS Bull. 31, 18 (2021).
(6) “Constraining the 12C+12C astrophysical S-factors with the 12C+13C measurements at very low energies”, N. T. Zhang, X. Y. Wang, D. Tudor*, B. Bucher, I. Burducea, H. Chen, Z. J. Chen, D. Chesneanu, A. I. Chilug, L. R. Gasques, D. G. Ghita, C. Gomoiu, K. Hagino, S. Kubono, Y. J. Li, C. J. Lin, W. P. Lin, R. Margineanu, A. Pantelica, I. C. Stefanescu, M. Straticiuc, X. D. Tang*, L. Trache*, A. S. Umar, W. Y. Xin, S. W. Xu, Y. Xu, Phys. Lett. B 801, 135170 (2020).
(7) “Modified astrophysical S-factor of 12C+12C fusion reaction at sub-barrier energies”, Y. J. Li, X. Fang*, B. Bucher, K. A. Li, L. H. Ru, X. D. Tang, Chin.Phys.C 44, 115001 (2020).
(8) “Status on 12C + 12C fusion at deep subbarrier energies: impact of resonances on astrophysical S* factors”, C. Beck, A. M. Mukhamedzhanov*, X. Tang, Eur. Phys. J. A 56, 87 (2020).
(9) “Gamow-Teller transitions to 93Zr via the 93Nb(t, 3He + γ) reaction at 115 MeV/u and its application to the stellar electron-capture rates”, B. Gao, R. G. T. Zegers, J. C. Zamora, D. Bazin, B. A. Brown, P. Bender, H. L. Crawford, J. Engel, A. Falduto, A. Gade , P. Gastis, T. Ginter, C. J. Guess, S. Lipschutz, A. O. Macchiavelli, K. Miki, E. M. Ney, B. Longfellow, S. Noji , J. Pereira, J. Schmitt, C. Sullivan, R. Titus, and D. Weisshaar, Phys. Rev. C 101, 014308 (2020).
(10) “An efficient method for mapping the 12C+12C molecular resonances at low energies”, Xiao-Dong Tang, Shao-Bo Ma, Xiao Fang*, Brian Bucher, Adam Alongi, Craig Cahillane, Wan-Peng Tan, NUCL SCI TECH 30, 126 (2019).
(11) “A Method for Determination of Deuterium Impurity in the Helium Beam”, Han Chen*, ShiWei Xu, NingTao Zhang, Jun Hu, KuoAng Li, ShaoBo Ma, XiChao Ruan, XiaoDong Tang, LiYong Zhang, Sci. China, Phys. Mech. & Astro. 61, 052021, Science China (2018).
(12) “β-decay rate of 59Fe in shell burning environment and its influence on the production of 60Fe in a massive star”, K.A. Li, Y.H. Lam, C. Qi, X.D. Tang, N.T. Zhang, Phys. Rev. C 94, 065807 (2016).
(13) “First Direct Measurement of 12C(12C, n)23Mg at Stellar Energies”, B. Bucher, X. D. Tang, X. Fang, A. Heger, S. Almaraz-Calderon, A. Alongi, A. D. Ayangeakaa, M. Beard, A. Best, J. Browne, C. Cahillane, M. Couder, R. J. deBoer, A. Kontos, L. Lamm, Y. J. Li, A. Long, W. Lu, S. Lyons, M. Notani, D. Patel, N. Paul, M. Pignatari, A. Roberts, D. Robertson, K. Smith, E. Stech, R. Talwar, W. P. Tan, M. Wiescher, S. E. Woosley, Phys. Rev. Lett. 114, 251102 (2015).