SEMINAR:- Experimental Challenge to the Big-Bang Nucleosynthesis(BBN) - The Lithium Problem in BBN
The primordial nucleosynthesis right after the big bang (BB) is one of the key elements that support the BB model. BBN is well known that it produced primarily light elements, and explains reasonably well the element abundance. However, there remains one serious problem, call the Li problem in BBN. The BBN simulation together with recent detailed micro-wave background measurements BBN explain most light elements including D, He-4, etc, but the Li-7 abundance is over predicted roughly by a factor of three.
The primordial Li-7 was considered to be produced mostly by the electron capture of Be-7 in the late stage of BBN. Thus, the question for nuclear physics side is whether Be-7 is overproduced or less destructed during the BBN stage. Since the production of Be-7 is by the He-3(α,γ) which is quite well known, the problem may be the destruction rate of Be-7. The Be-7(n,p) reaction is considered to be the main destruction reaction, but it is well investigated and thus it seems hard to change the rate by a factor of three. The next possible channel was Be-7(n,α) reaction, and almost no experimental works reported before. Recently, several experiments were performed or being performed by the direct and indirect methods. I will discuss these reaction studies of Be-7(n,α), including our activities and the result. The conclusion is that the reaction rate proposed by Wagoner et al. and currently being used is roughly one order of magnitude too large. Thus, the Li problem has not been solved, giving a more difficulty.
講者：Prof. Shigeru KUBONO (東京大學 理化學研究所仁科加速器研究中心)