How were the heavy chemical elements beyond iron made in the Universe
How were the heavy chemical elements beyond iron made in the Universe
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宇宙中除了铁之外的重化学元素是如何形成的
DOI：
10.1360/n972017-01368
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发表时间：
2018
影响因子：
--
通讯作者：
Gang Zhao
中科院分区：
文献类型：
--
作者：
J. He;B. Guo;Weiping Liu;Gang Zhao
核天体物理学是核物理学（微观尺度）和天体物理学（宏观尺度）的跨学科分支，解决宇宙中一些最引人注目的问题。研究工作致力于许多主题，例如化学元素的起源、地球上使生命成为可能的独特条件以及太阳、恒星和星系的形成和演化。核过程在大爆炸后的宇宙演化中发挥着极其重要的作用，除了为恒星提供抵抗重力的能量外，它们是唯一已知的合成重元素的机制。在过去的 50 年里，科学家们对大爆炸原始核合成和合成重元素的机制有了深入的了解。然而，天体物理模型尚未充分重现观测到的铁以外元素（称为超铁元素）的太阳丰度。人们普遍认为这些超铁元素主要是通过慢中子俘获过程（s-过程）和快中子俘获过程（r-过程）合成的。基本的 s 过程成分被认为源自热脉冲低质量 AGB 恒星，反应路径在稳定核素之后关闭。大约一半的重元素（最高可达铋）是通过 s 过程产生的。 r过程被认为发生在核心塌缩超新星和/或中子星合并的爆炸燃烧中。尽管r工艺地点仍然是个谜，但专家认为一半以上的超铁元素（最多钍和铀）是通过r工艺生产的。此外，还有 35 种缺乏中子的稳定同位素，它们在太阳系中的丰度要低得多。这些所谓的 p 核可能是在 II 型超新星中通过现有 s 或 r 过程种子的光解离（称为 p 过程或 r 过程）或通过最近提出的中微子质子 v p 过程产生的。天体物理模型需要大量的核物理输入数据。最重要的数据包括核质量、结构、衰变和裂变特征，以及沿各种核合成路径的相关核素横截面。迄今为止，缺乏系统和精确的核输入是科学家无法重现观测到的太阳超铁元素丰度的主要原因之一。美国国家研究委员会在 2002 年出版的《Discover》杂志上对“从铁到铀的重元素是如何制造的？”这一问题进行了排名。被誉为本世纪十大未解物理学问题之一。因此，迫切需要更完整、更精确的核物理输入来改进天体物理模型并解码观测结果。本文介绍了宇宙中产生超铁元素的最重要的核合成过程，同时还总结了天体物理模型所需的相关关键核物理输入。最后，本次野外研究的前沿包括超铁元素的起源，并对我国核天体物理研究的未来进行了展望。
Nuclear astrophysics, which is an interdisciplinary branch of nuclear physics (micro scale) and astrophysics (macro scale), addresses some of the most compelling questions in the universe. Research efforts have been devoted to many topics such as the origins of the chemical elements, the unique conditions of earth that makes life possible, and the formation and evolution of the sun, stars, and galaxies. Nuclear processes play an extremely important role in cosmic evolution after the Big Bang, and they are the only known mechanisms that synthesize heavy elements, in addition to providing the energy for stars to resist the force of gravity. Over the past 50 years, scientists have developed a deep understanding of Big-Bang primordial nucleosynthesis and the mechanisms for synthesizing heavy elements. However, the astrophysical models have yet to adequately reproduce the observed solar abundances of those elements beyond iron (referred to as ultra-iron elements). It is widely believed that these ultra-iron elements were primarily synthesized via the slow neutron capture process (s-process) and the fast neutron capture process (r-process). The fundamental s-process component is thought to originate from thermally pulsing low-mass AGB stars, with reaction pathways closed after the stable nuclides. About half of the heavy elements (up to bismuth) were produced via the s-process. The r-process is thought to occur in the explosive burning of core-collapse supernova and/or neutron-star mergers. Although the r-process site remains a mystery, experts believe that more than half of the ultra-iron elements (up to thorium and uranium) were produced via the r-process. In addition, there are 35 neutron-deficient stable isotopes, which are present in significantly less abundance in our solar system. These so-called p-nuclei are likely produced in Type II supernova, through the photo-dissociation (referred to as p-process or r-process) of existing s- or r-process seeds, or through the recently proposed neutrino-proton v p-process. Astrophysical models require a huge amount of nuclear-physics input data. The most essential data include nuclear mass, structure, decay and fission characteristics, and related nuclide cross-sections along the various nucleosynthesis paths. Thus far, the lack of systematic and precise nuclear inputs is one of the main reasons scientists have not been able to reproduce the observed solar abundances of ultra-iron elements. Published by Discover magazine in 2002, the American National Research Council ranked the question, "how were the heavy elements from iron to uranium made?" as one of the 11 Greatest Unanswered Questions of Physics in this Century . More complete and precise nuclear physics inputs are therefore urgently needed to improve astrophysical models and decode the observations. This paper introduces the most important nucleosynthesis processes that are responsible for the ultra-iron elements production in the universe, while also summarizing the relevant key nuclear-physics inputs required in the astrophysical models. Finally, the frontier in this field study includes the origins of ultra-iron elements, and the future of nuclear astrophysics research in China is examined.