Startup of the Fragment Mass Analyzer at ATLAS

Abstract The Fragment Mass Analyzer (FMA) is currently being brought into operation at the Argonne Tandem Linear Accelerator System (ATLAS). The FMA is a recoil mass spectrometer, 8 m in length, which will be used to separate nuclear reaction products from the primary beam and disperse them by mass/charge ( m / q ) at the focal plane. It has a solid angle of 8 msr, an energy acceptance of ±20% around the central energy, and an m / q acceptance of ±7% around the central mass. The FMA will allow the study of gamma rays originating from weak fusion-reaction channels by gating the gamma spectra by the desired ion identified at the FMA focal plane. Production and decay of nuclei far from stability will be studied at the FMA focal plane by implanting exotic recoils directly into detectors or by using a fast tape system to transport the recoils to shielded detector systems. With its capability of rotating from −5 to + 45° around the target, the FMA wil also be used for reaction mechanism studies. Beta-NMR and nuclear moment measurements will be made behind the focal plane. A facility description and a progress report on the commissioning of the FMA are presented.