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

¹ RIKEN Nishina Center, 2-1 Hirosawa, Wako, 351-0198, Saitama, Japan
² Institute of Modern Physics, CAS, Lanzhou, China
³ Center for Nuclear Study, University of Tokyo, 2-1 Hirosawa, Wako, 351-0198, Saitama, Japan

^a Corresponding author: kubono@riken.jp

Published online: 12 February 2016

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, ⁷Be and ⁷Li. The ⁷Be(n,α) reaction, which destroys ⁷Be, is considered to have a large impact to the primordial ⁷Li 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 ⁷Li problem. Under a proton-rich environment at high temperature like the νp-process, the ⁷Be(α,γ)¹¹C(α,p)¹⁴N 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 ⁷Be and ¹¹C. 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 ⁷Li(n,γ)⁸Li(α,n)¹¹B 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 ⁷Li(n,γ)⁸Li seems well confirmed, but the second step reaction ⁸Li(α,n)¹¹B still is not well known yet, whose status of the study is discussed.