arXiv 1405.02102014-05-01nucl-th

β衰变对r过程的局域和整体效应

Local and global effects of beta decays on r-process

O. L. Caballero, A. Arcones, I. N. Borzov, K. Langanke, G. Martinez-Pinedo

备注：: 11 pages, 7 figures, submitted to PRC

摘要：

核β衰变率是模拟天体物理r过程的一个基本要素。这些比率中的大多数仍然依赖于理论模型。然而，现代放射性离子束设施已经允许测量某些核的β半衰期或接近r-过程路径。这些数据表明，r-过程半衰期一般短于基于有限范围液滴模型（FRDM）的标准理论预测。这些数据也作为重要的约束条件，改进预测的半衰期的基础上连续QRPA计算顶部的能量密度泛函理论。虽然这些计算还局限于球形核，但它们包括接近和处于中子幻数$N=50, 82$和126的重要r过程等待点核。我们已经研究了这些新的实验和理论半衰期的影响，在两个天体物理站点的r-过程核合成目前青睐的r过程：中微子驱动的风，从新诞生的中子星在超新星爆炸和喷出物的合并两个中子星。我们发现，在一般情况下，较短的β衰变率有几个重要的影响的r-过程核合成的动力学。首先，物质流更快地克服等待点核，增强物质向更重的核的输运。其次，较短的半衰期也导致中子的更快消耗，从而导致冻结条件的重要变化，并对最终的r过程丰度产生影响。除了这些全球的r-过程动力学的影响，新的半衰期也导致一些局部的丰度分布的变化。

英文摘要：

Nuclear beta decay rates are an essential ingredient in simulations of the astrophysical r-process. Most of these rates still rely on theoretical modeling. However, modern radioactive ion-beam facilities have allowed to measure beta half lives of some nuclei on or close to the r-process path. These data indicate that r-process half lives are in general shorter than anticipated in the standard theoretical predictions based on the Finite Range Droplet Model (FRDM). The data have also served as important constraints for improved predictions of half lives based on continuum QRPA calculations on top of the energy-density functional theory. Although these calculations are yet limited to spherical nuclei, they include the important r-process waiting point nuclei close to and at the neutron magic numbers $N=50, 82$ and 126. We have studied the impact of these new experimental and theoretical half lives on r-process nucleosynthesis within the two astrophysical sites currently favored for the r process: the neutrino-driven wind from the freshly born neutron star in a supernova explosion and the ejecta of the merger of two neutron stars. We find that the, in general, shorter beta decay rates have several important effects on the dynamics of r-process nucleosynthesis. At first, the matter flow overcomes the waiting point nuclei faster enhancing matter transport to heavier nuclei. Secondly, the shorter half lives result also in a faster consumption of neutrons resulting in important changes of the conditions at freeze-out with consequences for the final r-process abundances. Besides these global effects on the r-process dynamics, the new half lives also lead to some local changes in the abundance distributions.

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