Nuclear Astrophysics at McMaster with Stable and Radioactive Ion Beams

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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.