Theoretical Research for Synthesis of Uranium Elements in Supernovas

从铁到铀的重元素的起源是一个谜。据信，这种重元素是由快速中子捕获过程（r过程）产生的，在这个过程中，种子核在很短的时间内非常迅速地捕获了许多中子。在过去的50年里，核心坍缩超新星一直被认为是r过程核合成的第一个候选者。这里最大的问题是，除了少数情况外，流体动力学模拟不可能产生足够高的熵来导致成功的r过程达到其第三个峰值。在这项研究中，我们已经证明了二维流体动力学模拟可以自然地获得r过程所需的高熵。此外，我们的模型还具有中子丰富和快速膨胀的特点。所有这些都是一个成功的超新星模型为r过程核合成提供环境的必要条件。因此，基于我们对核心坍缩超新星的流体动力学模拟来研究r过程核合成是非常有前途的。在这项研究中，我们还开发了核反应网络超级计算的基础，并分别与未来的日本x射线卫星NeXT和Suzaku研究了r过程核素的核伽马射线和钛和镍同位素的电子捕获衰变x射线的探测可能性。

The origin of heavy elements from iron to uranium is a mystery. It is believed that such heavy elements were created by the rapid neutron capture process (the r-process), in which seed nuclei captures many neutrons very rapidly in a very short time. Core-collapse supernovae have been suggested for the last 50 years to be the first candidate to host the r-process nucleosynthesis. The biggest problem here is that, except a few cases, hydrodynamical simulations could not have produced high-enough entropy to lead to a successful r-process up to its 3rd peak. In this research, we have demonstrated that a 2-Dimensional hydrodynamical simulation can naturally attain such a high entropy required for the r-process. In addition, our models have features of neutron richness and a fast expansion. All of these are essential requirements for a successful supernova model to give an environment for the r-process nucleosynthesis. It is thus very promising to study the r-process nucleosyntheis based on our hydrodynamical simulations of core-collapse supernovae. In this research, we have also developed the base of nuclear reaction network supercomputing calculations, and have investigated the detection possibilities of nuclear gamma-rays from the r-process nuclides and electron-capture decay X-rays from titanium and nickel isotopes, with future Japanese X-ray satellites, NeXT and Suzaku, respectively.