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arXiv 2205.09262nucl-thastro-ph.SR
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恒星的核弱速率和核弱过程

Nuclear Weak Rates and Nuclear Weak Processes in Stars

Toshio Suzuki

摘要:

利用壳层模型计算了恒星环境中的核弱过程,包括伽莫夫-特勒(GT)跃迁和自旋-偶极跃迁,并将其应用于恒星核弱过程。指出了精确弱速率对天体物理过程研究的重要作用。利用$sd$壳层的弱速率研究了8-10 M $_{\odot}$恒星ONeMg核的演化.研究了Urca核过程对核的冷却和$^{20}$ Ne双电子俘获对核的加热。特别地,用Walecka和Behrs-B $\ddot{\mbox{u}}$ hring的多极展开方法计算了$^{20}$ Ne的第二禁戒跃迁的电子俘获率,并讨论了核的最终命运,即核坍缩或热核爆炸.本文将$pf$壳层的弱速率应用于Ia型超新星铁族元素的核合成。与太阳丰度相比,富中子铁同位素的过量生产问题现在已减少到两倍以内。利用推广的Kuo-Krenciglowa方法计算了反转岛中$A$ =31的Urca核对的弱相互作用率.用$pf$ - $sdg$壳计算了$^{78}$ Ni中的跃迁强度和电子俘获率,并与随机相近似和有效俘获率公式计算结果进行了比较. $β$ -$N$ =126同位素的衰变率用GT和第一禁戒跃迁进行评估。发现半衰期短于标准模型获得的半衰期。用新的壳模型哈密顿量计算了$^{13}$ C,$^{16}$ O和$^{40}$ Ar的中子核反应截面.对核合成,中微子探测,中微子振荡和中微子质量等级的影响进行了讨论。

英文摘要:

Nuclear weak rates in stellar environments are obtained by shell-model calculations including Gamow-Teller (GT) and spin-dipole transitions, and applied to nuclear weak processes in stars. The important roles of accurate weak rates for the study of astrophysical processes are pointed out. The weak rates in $sd$-shell are used to study the evolution of ONeMg cores in stars with 8-10 M$_{\odot}$. Cooling of the core by nuclear Urca processes, and the heating by double e-captures on $^{20}$Ne are studied. Especially, the e-capture rates for a second-forbidden transition in $^{20}$Ne are evaluated with the multipole expansion method of Walecka and Behrens-B$\ddot{\mbox{u}}$hring, and the final fate of the cores, core-collapse or thermonuclear explosion, are discussed. The weak rates in $pf$-shell are applied to nucleosynthesis of iron-group elements in Type Ia supernovae. The over-production problem of neutron-rich iron isotopes compared with the solar abundances is now reduced to be within a factor of two. The weak rates for nuclear Urca pair with $A$=31 in the island of inversion are evaluated with the effective interaction obtained by the extended Kuo-Krenciglowa method. The transition strengths and e-capture rates in $^{78}$Ni, important for core-collapse processes, are evaluated with the $pf$-$sdg$ shell, and compared with those obtained by the random-phase-approximation and an effective rate formula. $β$-decay rates of $N$ =126 isotones are evaluated with both the GT and first-forbidden transitions. The half-lives are found to be shorter than those obtained by standard models. Neutrino-nucleus reaction cross sections on $^{13}$C, $^{16}$O and $^{40}$Ar are obtained with new shell-model Hamiltonians. Implications on nucleosynthesis, neutrino detection, neutrino oscillations and neutrino mass hierarchy are discussed.

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