CAMS/LLNL ion source efficiency revisited

The Center for AMS, Lawrence Livermore National Laboratory (CAMS) modified high-intensity Cs+ sputter source has several key characteristics, including very high ion current output, that make it useful for AMS applications. Within the AMS community there have been suggestions that certain aspects of operation of a sputter ion source at very high output levels could result in low ionization efficiency and the likelihood of consuming (burning through) small samples without acquiring adequate statistics. This is of particular importance for small mass carbon targets. We have recently re-determined the carbon ionization efficiency of the CAMS sputter source using graphite targets derived from Oxalic Acid I & II and demonstrated relatively high ionization efficiency (∼33%) during the operation of these sources at high output levels. We also examine the relationship between ion source efficiency and sample size.