Measuring fusion with low-intensity beams using an active target: Performance of MuSIC@Indiana

Next generation radioactive beam facilities namely the Facility for Rare Isotope Beams (FRIB), enable measurement of the fusion cross-section for neutron-rich light nuclei almost to the drip-line. To overcome the low-intensity of these exotic beams, an active thick-target approach is necessary. Efficient measurement of the fusion cross-section at near-barrier energies is realized using a Multi-Sampling Ionization Chamber (MuSIC). The design, construction and characterization of MuSIC@Indiana are described. The device was commissioned by measuring the ¹⁸O+¹²C fusion excitation function for 11 MeV < E_cm < 20 MeV using CH₄ gas. With MuSIC@Indiana,15 points on the fusion excitation function are extracted using a single incident beam energy. Two-body events and proton capture events are cleanly distinguished from fusion on carbon. The resulting excitation function is shown to be in good agreement with literature data. Advanced analysis techniques provide a reduction in the uncertainty of the fusion energy (E_cm) by a factor of approximately three over the standard approach.