Recoil separator ERNA: Measurement of He-3(alpha, gamma)Be-7

The reaction He-3(alpha, gamma)Be-7 plays a key role for the understanding of the production of Li-7 in Big Bang nucleosynthesis as well as for the high energy component of the solar neutrino spectrum. The uncertainty in its absolute cross-section arises from systematic differences of the available data sets. In various experiments the cross-section was measured by the detection of the prompt gamma-rays or by the off-line observation of the gamma-rays following the Be-7 electron capture; in a few cases both observations were carried out. We report on a new approach based on the use of the recoil separator ERNA (European Recoil separator for Nuclear Astrophysics) to detect directly the Be-7 recoils as well as the prompt gamma-rays in coincidence with the recoils. We present technical details of the experimental setup, such as a recirculating He-3 gas target, a TOF-E end detector, and a Nal detector array. In addition, the measurement of the separator acceptance is discussed and compared to the expected recoil emittance. The feasibility of the approach is demonstrated by sample spectra, indicating cross-section determinations of He-3(alpha, beta)Be-7 in the energy range E-cm = 0.7-3.3 MeV with high precision and accuracy. (C) 2008 Elsevier B.V. All rights reserved.