This grant supports upgrade of an existing helium isotope mass spectrometer dedicated to measurements of rocks and minerals at Woods Hole Oceanographic Institution (WHOI). The current mass spectrometer is fully automated and has been operating continuously since the early 1980s but has many antiquated components. Components of the upgrade would include: 1) replacement of a PDP-11 computer control system with a modern Pentium PC running Windows XP; 2) upgrade of the cryogenic system replacement of helium compressor and one of two cold heads; 3) upgrade of the vacuum system new turbomolecular pumps and UHV valves; 4) installation of new ion optics, a Channeltron detector and development of a new ion source; and 5) acquisition of a new quadrupole mass spectrometer to premeasure sample gases prior to inlet into the magnetic sector of the noble gas mass spectrometer. The requested upgrade is expected to lower the detection limit of the system by roughly a factor 10 (to ~ 1000 atoms 3He). This would be accomplished by installing ion counting detection electronics and an energy filter (on the electron multiplier), by upgrading the ion source, and by upgrading the ultra high vacuum components. The upgraded mass spectrometer would facilitate studies of mantle dynamics/degassing based on high precision, low detection limit analyses of 3He/4He ratios in mantle minerals, including analysis of materials recovered from the Hawaiian Scientific Drilling Project, where only small samples are available for study. Cosmogenic 3He measurements will also be used to determine the exposure age of materials at the earth's surface to support paleoclimate studies (e.g, dating of glacial moraines) and research on landscape evolution. The upgraded He dedicated noble gas mass spectrometer is part of a WHOI cost center (the WHOI Isotope Geochemistry Facility) and will be available to WHOI scientists and students in ther MIT-WHOI joint Ph.D. program, and also to the broader U.S. science community. A new web site will be developed to advertise the analytical capabilities available in the IGF.
