The ³He(alpha,gamma)⁷Be reaction studied at LUNA

The nuclear physics input from the 3He(alpha,gamma)7Be cross section is a major uncertainty in the fluxes of Be-7 and B-8 neutrinos from the Sun predicted by solar models and in the Li-7 abundance obtained in big-bang nucleosynthesis calculations.
Here we report on a precision cross section measurement performed by the LUNA collaboration at Gran Sasso (Italy). At energies directly relevant to big-bang nucleosynthesis, the cross section has been studied by both the activation [1] and the prompt-gamma technique.
Using a windowless gas target, high beam intensity, a low background in beam gamma-detector and low background gamma-counting facilities, the 3He(alpha,gamma)7Bee cross section has been determined at 90-170 keV center-of-mass energy with a total uncertainty as low as 4%.

The new 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., Phys. Rev. Lett. 97, 122502 (2006)