Nuclear Astrophysics at McMaster with Stable and Radioactive Ion Beams

我的研究旨在回答两个乍一看似乎无关，但却千丝万缕联系在一起的问题：(1)我们周围的一切从哪里来？或者更具体地说，我们骨骼中的钙、我们呼吸的空气中的氧气以及其他东西的来源是什么？第二个问题：(2)为什么太阳是“温暖的”？或者更广泛地说，恒星是如何发光的？令人惊讶的是，大自然通过做第一件事来做第二件事。根据我们对物理定律的理解，为太阳这样的恒星提供能量的最有可能的来源是它们核心的核反应。在恒星的整个生命过程中，这些反应也会将轻元素转化为重元素。当一颗恒星因核燃料耗尽而“死亡”时，它所产生的元素会被送回太空，有时是温和的，有时是猛烈的(超新星)。在这些元素中，新的恒星和行星诞生，最终导致地球上的人类。因此，从字面上看，我们是由星尘(或者，不那么诗意地说，是核废料！)组成的。我的研究旨在通过研究地球实验室中的这些恒星核反应，为我们的宇宙遗产证实和充实这一范例的细节。我的研究经费让我的团队能够使用最先进的设备：粒子加速器，产生离子束，然后与“靶子”碰撞，以重现正在恒星中发生的反应；以及测量反应产物性质的“探测器”。通过这些测量，我们可以确定有关反应及其速率的详细信息。近年来，我的重点一直放在恒星爆炸上，比如超新星、新星和x射线爆发。在这项提议中，我们描述的项目将帮助我们更好地理解(1)X射线爆发是如何被“触发”的；(2)在新星爆炸中合成的元素有多重，它们可以被看到；以及(3)哪些元素是在超新星中形成的。这些实验将使核-天体物理界的其他人受益，因为结果将被输入恒星的计算机模型，在计算机模型中探索它们对能量产生和核合成的影响。由于所有这些恒星都很热，关键的核反应往往涉及不稳定的、奇异的元素，而不是普通的稳定元素。这带来了技术挑战，因为不稳定离子束的产生可能具有挑战性。我们已经并将继续在加拿大、美国、日本和欧洲的实验室工作，使用稳定和不稳定的光束。这一战略使我的团队与其他领先的国际团队之间实现了强有力的交叉培养，这对加拿大这一领域的整体健康至关重要，同时也为学生提供了极好的培训机会。简而言之，这项研究将确保加拿大和麦克马斯特大学将为这一不断增长和令人兴奋的研究领域做出自己的重要贡献。

My research aims to answer two questions that seem unrelated at first glance, but which are inextricably linked: (1) Where does everything around us come from? Or more specifically, what is the origin of the calcium in our bones, the oxygen in the air we breathe, and the rest? And the second question: (2) Why is the sun "warm"? Or more generally, how do stars shine? Amazingly, Nature does the second by doing the first. Given our understanding of physical laws, the most likely origin of the energy that powers stars like our sun is from nuclear reactions in their cores. Over the course of the star's life, these reactions also make heavy elements out of light ones. When a star "dies" by running out of nuclear fuel, the elements it cooked up are put back into space, sometimes gently, and sometimes violently ("supernova"). Out of these elements, new stars and planets are born, leading ultimately to human beings on Earth. We are thus literally made of stardust (or, less poetically, of nuclear waste!). My research aims to corroborate and flesh out the details of this paradigm for our cosmic heritage, by studying these stellar nuclear reactions in terrestrial laboratories. My research funding gives my team access to state-of-the-art equipment: particle accelerators to produce beams of ions that are then collided with a "target", in order to reproduce the reactions that are happening in the stars; and "detectors" to measure the properties of the reaction products. From these measurements, we determine detailed information about the reaction and its rate. My focus in recent years has been on stellar explosions like supernovae, novae, and x-ray bursts. In this proposal, we describe projects that will help us better to understand (1) how an x-ray burst is “triggered”; (2) how heavy are the elements synthesized in a nova explosion and can they be seen; and (3) which elements are made in a supernova. These experiments will benefit the rest of the nuclear-astrophysics community, in that the results will be put into computer models of stars, within which their implications for the energy generation and nucleosynthesis are explored. Since all these stars are very hot, the critical nuclear reactions often involve unstable, exotic elements instead of the garden-variety stable ones. This poses a technical challenge, because beams of unstable ions can be challenging to produce. We have been, and will be, working at laboratories in Canada, the USA, Japan and Europe, using both stable and unstable beams. This strategy has enabled a strong cross-fertilization between my group and other leading international teams, which is imperative for the overall health of the field in Canada, and which, also importantly, has provided excellent training opportunities for students. In short, this research will ensure that Canada and McMaster University will make their own important contribution to this growing and exciting research area.**