Explosive Nuclear Burning in the pp-Chain Region and the Breakout Processes

Abstract

The nuclear reactions in the pp-chain region and on the breakout process from the pp-chain region under very high temperature conditions are reviewed, and some possibilities for experimental investigation are discussed. The reactions discussed could play an important role typically for the primordial nucleosynthesis and supernova nucleosynthesis. Specifically, I discuss here the reactions starting from the two key nuclei, 7 Be and 7 Li. The 7 Be(n,α) reaction, which destroys 7 Be, is considered to have a large impact to the primordial 7 Li problem. Our recent estimate of the reaction rate indicates that the reaction rate can be about one order of magnitude smaller than the rate currently adopted, suggesting this channel has a minor effect for the 7 Li problem. Under a proton-rich environment at high temperature like the νp-process, the 7 Be(α,γ) 11 C(α,p) 14 N pathway is expected to play a majpr role for heavy element synthesis, comparable to the triple alpha process. These two reactions on the pathway were investigated by using low-energy, high-intensity RI beams of 7 Be and 11 C. The results support the theoretical prediction of heavy nucleus production at around mass 90-100 by the νp-process, where the anomalously abundant p-nuclei exist. The reactions on the breakout sequence of 7 Li(n,γ) 8 Li(α,n) 11 B are also discussed which could paly a crucial role in nuetron-rich envirnments, like in the primirdial universe as well as the early stage of the r-process. The cross sections of the first step reaction 7 Li(n,γ) 8 Li seems well confirmed, but the second step reaction 8 Li(α,n) 11 B still is not well known yet, whose status of the study is discussed.