The ³He(alpha,gamma)⁷Be reaction measured by activation at LUNA

The nuclear physics input from the 3He(alpha,gamma)7Be cross section is a major uncertainty in the fluxes of 7Be and 8B neutrinos from the Sun predicted by solar models and in the 7Li abundance obtained in big-bang nucleosynthesis calculations. In the seminar I will report on a new precision experiment on this reaction performed by the LUNA collaboration [1].

Using a windowless gas target, the high beam intensity of the LUNA2 accelerator, and the Gran Sasso low background gamma-counting facilities, the 3He(alpha,gamma)7Be cross section has been determined by the activation method at 90 -- 170 keV center-of-mass energy with a total uncertainty as low as 4%. The present low energies are directly relevant to big-bang nucleosynthesis and had previously been reached experimentally only by the prompt-gamma technique and with inferior precision.

The new LUNA data can be used in big-bang nucleosynthesis calculations and to constrain the extrapolation of the 3He(alpha,gamma)7Be astrophysical S-factor to solar energies.

[1] D. Bemmerer et al. (LUNA Collaboration), Phys. Rev. Lett. 97, 122502 (2006)