The University of Hawaii Ims 1280 Ion Microprobe

Introduction: In March, 2006, the Hawaii Institute of Geophysics and Planetology expects to take delivery of a new Cameca ims 1280 ion microprobe. The new ion probe will be the centerpiece of the W. M. Keck Cosmochemistry Laboratory and will be used to analyze extraterrestrial materials, including meteorites, interplanetary dust particles (IDPs), and samples returned by NASA missions. The 1280 is the newest incarnation of the large-geometry Cameca ion probe [1]. It uses a new generation of electronics to control the voltages in the primary-ion column and secondary-ion mass spectrometer. It has improved magnet control , including an improved Hall probe system and a new NMR system. It has computer control of all slits and apertures, new computer routines to improve re-producibility, and improved ion detectors. These new features give the 1280 better performance than earlier machines. For example, the 1280 can measure oxygen isotopic compositions of mineral grains at a spatial scale of ~25 microns with a precision and reproduci-bility of <0.5 permil (2σ) [2]. We will upgrade this highly capable instrument with additional state-of-the-art technologies to address the unique challenges of research on early solar-system materials. We will add a secondary-electron detector to aid in locating tiny grains for analysis. The secondary-electron image in the ion microprobe can be directly correlated with the secondary-electron image from an SEM. To help precisely position the sample under the primary beam during automated analyses and to facilitate using sample locations determined by an automated system on the SEM, we will add optical encoders to the sample stage. In collaboration with Prof. Yurimoto of Hokkaido University, we will add a new type of two-dimensional, solid-state detector called SCAPS [3, 4]. Dr. Nagashima, a member of our research team, is a co-developer of this unique detector. The SCAPS detector will permit direct ion imaging of fine-grained samples and will permit identification of isotopically or chemically anomalous grains at a spatial resolution of a few tenths of a mi-cron [e.g., 5, 6]. Direct imaging uses the mass spectrometer as an ion microscope and can use either a rastered or a defocused beam. The spatial resolution is controlled by either the ion optics of the mass spectrometer or the pixel size of the detector. In