A NEW DESIGN OF A CS SPUTTER ION-SOURCE FOR ACCELERATOR MASS-SPECTROMETRY

Accelerator mass spectrometry (AMS) requires ion sources delivering intense negative ion beams of high stability. In addition, a multitarget system and a vacuum lock for sample loading are essential for efficient operation. We present a new design of a cesium (Cs) negative ion sputter source with the following features: the vacuum chamber of the ion source and the target cassette are at ground potential. Batches of targets can be loaded and unloaded without interrupting the operation of the source. All control systems for sample loading and automatic changing are also at ground potential. This ion source concept has already been successfully applied to AMS at our laboratory. The new design incorporates a spherical Cs surface ionizer to increase the negative ion currents. Difficulties in realizing this concept are the high electric fields inside the vacuum chamber in an environment with high Cs vapor pressure. Also critical are the proper and reliable operation of all mechanical components under these conditions and the large temperature gradients.