Underground Study of Stellar Neutron Sources for Trans-Fe Element Production in Stars

South Dakota School Of Mines And Technology, Rapid City SD

Investigators

Abstract

The origin of the elements has been identified by the Nuclear Science Advisory Committee as one of the most important questions of our day. Current astronomical observations indicate that many elements found commonly on Earth were first synthesized in the center of stars, where fusion and other nuclear reactions take place. These nuclear reactions control the associated energy generation and evolution of stars. However, the stellar conditions are difficult to reproduce in the laboratory. Under the special conditions proposed here, using a novel compact accelerator placed deep underground, some of the key nuclear reactions that take place in stars can be measured. The goal of this research is to measure nuclear processes that are part of a chain of reactions leading to the synthesis of elements. These are the elements that make possible life on Earth. The project seeks to study the strength of stellar neutron sources that drive the s-process, one of the two dominant sources for the production of heavy elements. One of the most critical processes is alpha-particle induced reactions on Ne-22, producing Mg-25 plus a neutron, but other alpha-neutron reactions may also play a role depending on the stellar environment. However, the large cosmic ray induced neutron background has been prohibitive for advancing these measurements into the stellar energy range and the present reaction rates rely on theoretical extrapolations that carry high uncertainties. There has been no facility where these measurements can be pursued in a background neutron free environment. Over the past years the CASPAR (Compact Accelerator System for Performing Astrophysical Re¬search) instrumentation has been constructed at the Sanford Underground Research Facility to address this need. CASPAR operates a 1 million-Volt, high intensity, fully refurbished Van de Graaff accelerator that can provide alpha beam intensities of several hundred micro-Ampere. The proposed experiments rely on the use of a solid and a recirculating gas target system and a He-3 detector system for neutron counting. Successful implementation of a science program at CASPAR will offer a competitive opportunity for the US nuclear astrophysics community to maintain leadership in the field. It will provide a world-wide unique opportunity to study stellar helium burning reactions associated with the synthesis of carbon and the neutron production for trans-iron nuclei.