Travel grant to support experiment at MSU on r-process nuclei

在超新星爆炸中，大质量恒星在快速坍缩中结束生命，随后发生爆炸，将大部分恒星物质喷射到太空中。这种爆炸是所谓的r过程的主要候选者之一，地球上许多最重的化学元素都是在r过程中产生的。在导致爆炸的恒星坍缩过程中，阻止坍缩的电子被恒星中存在的原子核迅速吸收。随着电子被吸收，恒星不再稳定，恒星的坍缩不可避免。由于坍缩的剧烈，恒星的外层随后在超新星爆炸中被抛入太空。长期以来，人们一直认为氢的质子对电子的吸收起主导作用，而在r过程中产生的原子核则被排除在外。这是因为r过程核的内部结构被认为完全阻止了电子的吸收。然而，这种封锁现在正受到质疑。最近的研究表明，富含中子的r过程核的结构效应可能为这些核上的电子吸收开辟了潜在的空间，甚至在某种程度上它们成为坍缩的主要原因。为了澄清这一点，我们将在实验中考察r过程核中单个核子（即质子和中子）的结构。这项研究将利用单个核子从短寿命r过程核中被敲除的反应。在实验中，敲除过程以及在反应中产生的核状态随后将被研究。

In supernova explosions, massive stars end their life in a rapid collapse followed by an explosion that ejects a large fraction of the stellar material into space. This kind of explosion is one of the prime candidates for the so-called r-process in which many of the heaviest chemical elements on Earth are produced. In the stellar collapse that drives the explosion, the electrons which hold back the collapse are rapidly absorbed by the atomic nuclei present in the star. As electrons are absorbed, the star is no longer stable and the collapse of the star inevitable. Because of the violence of the collapse, the outer layers of the star are subsequently flung into space in a supernova explosion. The protons from hydrogen have long been thought to dominate the absorption of electrons, whereas nuclei produced in the r-process have been excluded. This is because the internal structure of r-process nuclei has been thought to completely block the absorption of electrons. This blocking, however, is now being questioned. It has recently been shown that structural effects in the neutron-rich r-process nuclei can potentially open up for absorption of electrons on these nuclei, even to the degree where they become the dominant contributor to the collapse. To clarify this, the configuration of individual nucleons (that is, protons and neutrons) in r-process nuclei will be examined in the experiment. This investigation will utilise reactions where individual nucleons are knocked out of the short-lived r-process nuclei. In the experiment, both the knockout process as well as the nuclear states produced in the reactions will subsequently be investigated.