Langanke K, Martínez-Pinedo G, Zegers R G T
GSI Helmholtzzentrum für Schwerionenforschung, D-64291 Darmstadt, Germany.
Institut für Kernphysik (Theoriezentrum), Department of Physics, Technische Universität Darmstadt, D-64298 Darmstadt, Germany.
Rep Prog Phys. 2021 May 21;84(6). doi: 10.1088/1361-6633/abf207.
Electron capture on nuclei plays an essential role in the dynamics of several astrophysical objects, including core-collapse and thermonuclear supernovae, the crust of accreting neutron stars in binary systems and the final core evolution of intermediate-mass stars. In these astrophysical objects, the capture occurs at finite temperatures and densities, at which the electrons form a degenerate relativistic electron gas. The capture rates can be derived from perturbation theory, where allowed nuclear transitions [Gamow-Teller (GT) transitions] dominate, except at the higher temperatures achieved in core-collapse supernovae, where forbidden transitions also contribute significantly to the capture rates. There has been decisive progress in recent years in measuring GT strength distributions using novel experimental techniques based on charge-exchange reactions. These measurements not only provide data for the GT distributions of ground states for many relevant nuclei, but also serve as valuable constraints for nuclear models which are needed to derive the capture rates for the many nuclei for which no data yet exist. In particular, models are needed to evaluate stellar capture rates at finite temperatures, where capture can also occur on nuclei in thermally excited states. There has also been significant progress in recent years in the modeling of stellar capture rates. This has been made possible by advances in nuclear many-body models as well as in computer soft- and hardware. Specifically, to derive reliable capture rates for core-collapse supernovae, a dedicated strategy has been developed based on a hierarchy of nuclear models specifically adapted to the abundant nuclei and astrophysical conditions present under various collapse conditions. In particular, for the challenging conditions where the electron chemical potential and the nuclearvalues are of the same order, large-scale shell-model diagonalization calculations have proved to be an appropriate tool to derive stellar capture rates, often validated by experimental data. Such situations are relevant in the early stage of the core collapse of massive stars, for the nucleosynthesis of thermonuclear supernovae, and for the final evolution of the cores of intermediate-mass stars involving nuclei in the mass range∼ 20-65. This manuscript reviews the experimental and theoretical progress recently achieved in deriving stellar electron capture rates. It also discusses the impact these improved rates have on our understanding of the various astrophysical objects.
原子核上的电子俘获在多个天体物理对象的动力学过程中起着至关重要的作用，这些对象包括核心坍缩超新星和热核超新星、双星系统中吸积中子星的地壳以及中等质量恒星的最终核心演化。在这些天体物理对象中，俘获发生在有限的温度和密度下，此时电子形成简并相对论电子气。俘获率可以从微扰理论推导得出，其中允许的核跃迁（伽莫夫-泰勒（GT）跃迁）占主导，除了在核心坍缩超新星达到的较高温度下，此时禁戒跃迁对俘获率也有显著贡献。近年来，基于电荷交换反应的新型实验技术在测量GT强度分布方面取得了决定性进展。这些测量不仅为许多相关原子核基态的GT分布提供了数据，还为推导许多尚无数据的原子核的俘获率所需的核模型提供了有价值的约束。特别是，需要模型来评估有限温度下的恒星俘获率，此时俘获也可能发生在热激发态的原子核上。近年来，在恒星俘获率的建模方面也取得了重大进展。这得益于核多体模型以及计算机软硬件的进步。具体而言，为了推导核心坍缩超新星可靠的俘获率，已经基于专门适用于各种坍缩条件下存在的丰富原子核和天体物理条件的核模型层次结构制定了一种专门策略。特别是，对于电子化学势和核值处于同一量级的具有挑战性的条件，大规模壳模型对角化计算已被证明是推导恒星俘获率的合适工具，并且经常通过实验数据进行验证。这种情况在大质量恒星核心坍缩的早期阶段、热核超新星的核合成以及涉及质量范围约为20 - 65的原子核的中等质量恒星核心的最终演化中都很重要。本手稿回顾了最近在推导恒星电子俘获率方面取得的实验和理论进展。它还讨论了这些改进的俘获率对我们理解各种天体物理对象的影响。
