Underground Low-Background Nuclear Astrophysics Studies

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CASPAR (Compact Accelerator System for Performing Astrophysical Research) is the first and only deep underground accelerator laboratory in the United States and only the second existing in the world. It will be located nearly a mile underground at the Sanford Underground Research Facility in Lead, South Dakota. Nuclear Astrophysics will be studied there and the focus of the studies will be the early stages of light elemental synthesis in primordial stars (the first stars formed after the Big Bang). The nuclear interactions involving light elements in stellar environments are the foundation for the production of all elements in the Universe. This work will provide data to explain the abundance of elements that are observed by astronomers in the oldest stars of our Universe; and an investigation of the source of neutrons that drive these processes will provide a more complete picture of the nuclear burning in these stars that facilitate the production of the heavier elements.Laboratory studies of nucleosynthesis in stars are difficult to perform near the surface of the earth due to an enormous background from cosmic ray interactions in the atmosphere which overwhelm the experiment. Therefore, this work will utilize a 1 Mega Volt electrostatic accelerator located 4850 ft underground at the Sanford Underground Research Facility (SURF) to perform experiments that exploit the low cosmic ray background conditions at CASPAR. The acceleration and subsequent bombardment of a range of elements of interest (for example carbon and neon) with proton and alpha ion beams, will result in the emission of neutrons and gamma rays to be analyzed with Sodium Iodide (NaI) summing detectors and deuterated liquid scintillator arrays. The facility is nearly unique in the world. It is comparable to the LUNA facility in Italy and one proposed in China; but neither competitor will cover as broad an energy range as CASPAR. CASPAR is a part of the nuclear astrophysics program at the University of Notre Dame. The unique nature of the proposed research will support the education of graduate students working in Nuclear Physics and the training of the nation's future nuclear workforce. CASPAR is supported by the National Science Foundation and is synergistic with other important NSF initiatives such as the frontier center for nuclear astrophysics, JINA-CEE and the gravitational-wave observatory, LIGO.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.