Abstract
Experiments with low-energy rare ion beams often suffer from a large amount of molecular contaminant ions. We present the simple isolation-dissociation-isolation method to suppress this kind of contamination. The method can be applied to almost all types of low-energy beamlines. In a first step, a coarse isolation of the mass-to-charge ratio of interest is performed, e.g. by a dipole magnet. In a second step, the ions are dissociated. The last step is again a coarse isolation of the mass-to-charge ratio around the ion of interest. The method was tested at the FRS Ion Catcher at GSI with a radioactive ion source installed inside the cryogenic stopping cell as well as with relativistic ions delivered by the synchrotron SIS-18 and stopped in the cryogenic stopping cell. The isolation and dissociation, here collision-induced dissociation, have been implemented in a gas-filled RFQ beamline. A reduction of molecular contamination by more than 4 orders of magnitude was achieved.
Highlights
A common problem faced when using low-energy beams of exotic nuclei is molecular contamination
Reduction or complete removal of this contamination is important for experiments at low-energy rare ion beam (RIB) facilities
The isolation steps can be performed for DC beams by a dipole magnet [3] or RF mass filter [7] and for pulsed beams with a Bradbury-Nielsen gate [8]. This method of consecutive steps of isolation, dissociation and again isolation is the so-called IDI method (Fig. 1) and is described in the following. This method was successfully tested in the RFQ beamline at the Fragment Separator (FRS) Ion Catcher (FRS-IC), GSI
Summary
A common problem faced when using low-energy beams of exotic nuclei is molecular contamination. Molecular ions with a mass-tocharge ratio larger than that of the IOI might break up into fragments with a mass-to-charge ratio of the IOI, so the molecular contamination of the IOI is only changed, but not removed. This problem is solved by applying an isolation step before the dissociation. The isolation steps can be performed for DC beams by a dipole magnet [3] or RF mass filter [7] and for pulsed beams with a Bradbury-Nielsen gate [8] This method of consecutive steps of isolation, dissociation and again isolation is the so-called IDI method (Fig. 1) and is described in the following. This method was successfully tested in the RFQ beamline at the FRS Ion Catcher (FRS-IC), GSI
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