Using the FMA for radiative capture cross-section measurements of interest to astrophysics

Abstract

We assessed the capability of the Fragment Mass Analyzer (FMA) to study radiative capture reactions of astrophysical interest using inverse kinematics. Results from measurements on the {sup 1}H({sup 13}C,{sup 14}N){gamma} reaction show that the FMA is an ideal high-efficiency tool for these experiments, where the recoil ion is detected and identified at the FMA focal plane. Intermediate slits acting on energy/charge and mass/charge were introduced into the FMA, which reduced the scattered primary beam fraction at the focal plane to <10{sup -11}. A small gas ionization chamber was placed behind the position-sensitive focal-plane detector, followed by a Si detector. Measurements of mass/charge, energy loss, and residual energy of the transmitted ions were made, giving at least another two orders of magnitude separation of recoils from scattered beam. A new ionization detector operating in the same gas volume as the focal plane detector will provide even better separation by eliminating the need for two of the three windows used in the test measurement. At energies of {approximately} 0.5 MeV/nucleon, the recoil ions populate primarily a single charge state, resulting in a detection efficiency of > 50%. This will be particularly valuable for use with radioactive beams.