Stellar Archeology: The Nuclear Fingerprints of Massive Stars.

宇宙中所有比氦重的元素都是在恒星的核心通过核反应产生的。大质量恒星，即由比我们的太阳更多的物质组成的恒星，被认为在产生我们今天在自然界中发现的大量化学元素方面发挥了重要作用。关于这些元素的起源，特别是那些比铁重的元素，以及它们形成的天体物理条件，仍然有许多悬而未决的问题。通过结合现代天文学、陨石样品的同位素分析和微观核物理学的观察，人们对元素是如何形成的有了前所未有的了解。然而，我们对恒星如何锻造化学元素的预测，关键取决于我们对制造它们的潜在核反应的了解。许多重要的反应涉及自然界中找不到的短寿命放射性核，因此必须在实验室中生产。我们现在正进入研究放射性同位素核反应的黄金时代，几个新的设施正在投入使用，如稀有同位素束设施（美国）、高级稀有同位素实验室（加拿大）和欧洲核子研究组织的HIE-ISOLDE升级。我的研究旨在利用这些一流的实验室来研究天体物理反应，这是理解大质量恒星内部元素如何形成的关键。许多谜团围绕着第一批恒星中元素的形成以及比铁更重的元素的出现。第一批恒星被认为比我们的太阳大得多，因此很快就燃烧了它们的核燃料。这意味着今天很少有人能直接观察到，尽管詹姆斯韦伯太空望远镜将使我们更接近实现这一目标。相反，像考古学家一样，我们必须从它们留下的指纹中拼凑出它们的进化，这些指纹保存在第一代之后形成的非常古老的恒星中的不同元素中。然而，将这些化学指纹与第一批恒星的特征联系起来，需要我们正确理解制造它们的核反应。我的研究的一个关键重点是集中在核反应的测量，这将使我们能够利用观测来更好地了解早期宇宙中元素的创造，特别是对重元素的起源知之甚少。另一个与重元素的起源有关的谜团，是由一组被称为“p核”的特殊同位素的未知起源引起的。这30种左右的同位素占比铁重的原子核的不到1%，并且不能通过正常的重元素生产机制形成。相反，我们认为它们可能是在核心坍缩的超新星中产生的，这种剧烈的爆炸结束了大质量恒星的生命。然而，目前，我们最好的模型无法重现陨石样本中看到的p核数量，这保留了超新星的化学指纹。由于极端的技术挑战，这些预测受到尚未测量的不稳定同位素的关键反应的影响。最近，我共同领导了一项实验，首次测量了这些反应之一，通过这项奖学金，我将继续领导一项在新设施上进行进一步测量的计划，以了解p核的起源。

All the elements in the universe heavier than helium were created inside the cores of stars by nuclear reactions. Massive stars, that is, stars made of much more matter than our Sun, are believed to have played an essential role in producing the vast number of chemical elements we find in nature today. There are still many open questions related to the origin of the elements, particularly those heavier than iron, and the astrophysical conditions in which they were made. Unprecedented insight into how the elements were created is gained through combining observations from modern astronomy, isotopic analysis of meteorite samples, and microscopic nuclear physics. However, our predictions as to how stars forged the chemical elements rely critically on our knowledge of the underlying nuclear reactions that made them. Many important reactions involve short-lived radioactive nuclei not found in nature, and so must instead be produced in the laboratory. We are now entering into a golden-era for studies of nuclear reactions on radioactive isotopes, with several new facilities now coming into operation, such as the Facility for Rare Isotope Beams (United States), the Advanced Rare Isotope Laboratory (Canada) and the HIE-ISOLDE upgrade at CERN. My research aims to use these premier laboratories to study the astrophysical reactions that are key to understanding how elements are made inside massive stars.Many mysteries surround how elements were made in the first stars and the emergence of elements heavier than iron. The first stars are believed to have been by far larger than our Sun, and so burned their nuclear fuel quickly. This means that few are left to observe directly today, though the James Webb Space Telescope will take us much closer to achieving this goal. Instead, like archeologists, we must piece together their evolution from the fingerprints they leave behind, preserved in the different elements seen in very old stars formed after this first generation. However, relating these chemical fingerprints to the characteristics of the first stars requires us to properly understand the nuclear reactions that made them. A key focus of my research is centred on measurements of nuclear reactions that will allow us to use observations to better understand the creation of elements in the early universe, especially the poorly understood origins of the heavy elements. Another mystery, related to origin of the heavy elements, is posed by the unknown origin of a special group of isotopes called the "p-nuclei". These 30 or so isotopes account for less than 1% of the nuclei heavier than iron and cannot be formed by the normal heavy-element production mechanisms. Instead, we believe they might be produced in core-collapse supernovae, the violent explosions ending the life of massive stars. Currently, however, our best models are unable to reproduce the amounts of p-nuclei seen in meteorite samples, which preserve the chemical fingerprints of supernovae. These predictions are affected by key reactions on unstable isotopes that haven't yet been measured, due to extreme technical challenges. Recently, I co-led an experiment which measured one of these reactions for the very first time and, through this fellowship, I will continue to lead a program of further measurements at new facilities to understand the origins of the p-nuclei.