Low-Background Nuclear Astrophysics Studies a Mile Underground

Particle interactions of importance to nuclear astrophysics are the priority of the CASPAR (Compact Accelerator System for Performing Astrophysical Research) research instruments. CASPAR is the first and only deep underground accelerator laboratory in the United States and only the third existing in the world. It is located nearly a mile underground at the Sanford Underground Research Facility (SURF) in Lead, South Dakota.

This award will support researchers using gamma and particle detection techniques, to focus on the study of 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. Additional investigations will study the source of neutrons that drive these processes and will provide a more complete picture of the nuclear burning in stars that facilitates the production of the heavier elements.

Understanding these processes is crucial for our understanding of multi-messenger astrophysical sources and thus addresses goals of NSF's "Windows on the Universe: The Era of Multi-Messenger Astrophysics.

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 that overwhelm the experiment. Therefore, this work will utilize a 1 Mega Volt electrostatic accelerator located 4850 ft underground at 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 boron 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 JUNA in China.

CASPAR is a collaboration between the nuclear astrophysics programs at the University of Notre Dame and the South Dakota School of Mines and Technology. 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.

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.