Upgrade of Noble Gas Mass Spectrometer (VG5440) for Use in the Earth and Environmental Sciences

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This award will permit the upgrade of the electronics units of a noble gas mass spectrometer (VG5440) which has now been in operation for over 18 years. The upgrade will restore and significantly enhance the measurement capabilities of the machine so that we can initiate new studies in the field of neon and nitrogen isotope geochemistry. We plan to or are pursuing studies in 4 areas of contemporary Ne and N2 research: (1) Surface exposure dating using cosmogenic 21Ne. We plan improvements in the methodology of identifying cosmic-ray-produced 21Ne in natural materials, specifically to resolve discrepancies between ages based on 21Ne, 10Be and 26Al nuclides. (2) Neon isotope systematics of ocean island basalts (OIB). We plan to search for Ne isotopic heterogeneity in various classes of OIB. We seek to further evaluate the relationship between He and Ne by targeting Icelandic (and other OIB) samples which have amongst the highest 3He/4He values worldwide. (3) Groundwater recharge studies utilizing Ne isotopes. Neon has the potential to identify mechanisms of groundwater recharge through studies of the 'excess air' component identified in some aquifer systems. (4) Defining the nitrogen isotope systematics of the 'enriched' mantle. We have targeted Iceland and the adjacent Reykjanes Ridge as prime localities to gain insight into the characteristic N-isotope variations of the terrestrial mantle. Furthermore, this proposal will update a dedicated neon isotope facility whose primary role is training of graduate students and post-doctoral visitors. To date, a significant number of established researchers have received their training in noble gas geochemistry using the Scripps/UCSD laboratories and this funding will allow this tradition to continue.