The study of radiative capture nuclear reactions by direct detection of the reaction products can be performed using a recoil separator. In this technique recoil ions and beam particles (both having the same momentum) are separated by velocity or energy filters. Focussing elements counter the opening angle induced on the recoil ions by the g-ray emission. Such a device, the European Recoil Separator for Nuclear Astrophysics (ERNA) was set up in the Dynamitron Tandem Laboratory of the Ruhr-University Bochum.
In the talk, I will discuss several experimental key points like gas target properties, charge state distributions, acceptance measurements and suppression. The first two reactions studied with the recoil separator were 12C(a,g)16O and 3He(4He,g)7Be – key reactions in nuclear astrophysics. The peculiarities in the measurement of those reactions and their results are presented.