A new focal-plane detector system for low fusion-evaporation cross section measurements

A new focal-plane detector system has been designed and constructed for measuring very small heavy-ion induced fusion-evaporation cross sections with the Fragment Mass Analyzer (FMA) at Argonne National Laboratory. The system has been tested and successfully used in a fusion-evaporation excitation function measurement for 64Ni+100Mo down to the 5 nb level. The design and performance of the detector system are described in detail with some examples from the latest data. Besides excellent tracking capabilities for each event measured in the detector, suppression of scattered beam background of the order of 4×10-17 has been demonstrated.