An exploratory study of recycled sputtering and CsF2− current enhancement for AMS

The analysis of 135Cs/Cs ratios at levels below 10−12 by accelerator mass spectrometry (AMS) would preferably use commonly available negative ion injection systems. The sputter ion sources in these injectors should ideally produce currents of Cs− or Cs-containing molecular anions approaching μA levels from targets containing mg quantities of Cs. However, since Cs is the most electro-positive stable element in nature with a low electron affinity, the generation of large negative atomic, or molecular beams containing Cs, has been very challenging. In addition, the reduction of the interferences from the 135Ba isobar and the primary 133Cs+ beam used for sputtering are also necessary. The measurement of a wide range of the isotope ratios also requires the ion source memory of previous samples be minimized. This paper describes some progresses towards a potential solution of all these problems by recycled sputtering using fluorinating targets of PbF2 with mg CsF mixed in. The problems encountered indicate that considerable further studies and some redesign of the present ion sources will be desirable.