An improved sample changer system for use in conjunction with a new ion source has been designed and built at PRIME Lab. It is based on the “rabbit” sample changer developed at Chalk River Nuclear Laboratories in Canada. This sample changer allows continuous running of the ion source without disturbing its vacuum or voltage. Cathodes are shuttled from a 51-position, rotatable cassette, at ground potential and near-atmospheric pressure, through a non-conducting tube (like a rabbit hole) into a receiving position in a stainless steel sample rod, which is at the high voltage potential of the ion source. The rod lowers the cathode past two pumping stages into the vacuum of the source. After AMS measurement, the process is reversed to return the cathode to the cassette. Sample cassettes may be interchanged without interrupting the operation of the source.
When the rod is up, a television camera is utilized to view the location and focus of the cesium spot on the cathode, and to sense the cathode position; a three-dimensional stage allows positioning of the cathode. The image from this camera is captured and serves as an indication for successful transport of the cathode into the sample rod. Although operation of the system was reliable from the start, some failures were found during testing and operation. Sensors have been added to verify the completion of cathode transport and sample rod movements. Exposure of the raised sample rod to air (presumably water vapor) caused difficulty in sustaining the vacuum, so a N2 gas enclosure surrounding the raised rod was added. All control of the sample changer and reading of the sensors is done by a PC, using LabView, which interfaces to the LabView control of the entire AMS process.
All design of the sample changer (and the ion source) was done using a CAD program (Autodesk Inventor) which employs three-dimensional, parametric modeling so that design of parts can be assembled, visualized, tested, and modified before construction of the equipment. This has been critical in the building of such an innovative device.
In addition to further improvements in cathode transport reliability and source vacuum, we anticipate in the near future implementing a scannable cathode marking system utilizing a two-dimensional data matrix laser-etched to bottom of the cathodes for identification purposes. These markings can be read by both handheld and machine mounted devices.
See more of Poster Session II
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)