THE WiscSIMS NATIONAL FACILITY FOR STABLE ISOTOPE GEOCHEMISTRY
The University of Wisconsin SIMS lab (WiscSIMS) was installed in 2005 and became a National Facility for Stable Isotope Geochemistry in 2008 with support from NSF, Division of Earth Sciences, Instrumentation and Facilities Program (link). A primary goal of WiscSIMS is to provide experienced and inexperienced SIMS users with the best possible analytical precision and accuracy for in situ analysis of stable isotope ratios at the scale of 1 to 10 micrometers. We can also provide advice and assistance on a range of related scientific and technical issues. The unique ion microprobe capabilities permit analyses in thin section or polished mount to be correlated with textures and information from optics, imaging, or other forms of instrumental analysis. In combination, such data can provide fundamental new levels of understanding for samples of Geological, Planetary, or Biological interest. The advantages are especially great for samples that are zoned, precious, or very small, which can’t be analyzed by other means. In 2005-2014, over 130 scientists from 60 universities and research institutes worked with WiscSIMS and published their results.
The WiscSIMS lab houses a CAMECA IMS-1280. The IMS-1280 is a large radius multi-collector ion microprobe incorporating many improvements over earlier instruments, several of which are designed to enhance precision and accuracy of isotope ratio analysis. The detector assembly includes a total of 10 electron multiplier and Faraday Cup detectors with five moveable trolleys for simultaneous analysis of a wide range of isotope systems. Both alkali metal (Cs+) and duoplasmatron (O-, O+) sources are available. Spot sizes as small as 250 nm are possible (with Cs), but more generally, a spot of 10 μm diameter by 1 μm deep is used to increase sample size (~1ng/analysis) and optimize accuracy and precision. Precision for δ18O and δ17O in well-polished silicates is typically ±0.3‰, (2 SD, spot-to-spot) with 10 μm diameter spots (Kita et al. 2009 Chem Geol; Valley & Kita 2009 MAC Shortcourse v 41).
As of 2014, the lab has experience with analysis of Li, C, O, Mg, Si, and S isotope ratios. Best results come from well-prepared samples that are vacuum stable, have a smooth, flat, low-relief surface, are 25 mm in diameter and <6 mm thick (see our sample preparation page). Surface relief is minimized by careful polishing and is measured at sub-μm-scale by white light profilometer. Other materials can be analyzed, as can isotope ratios for trace elements. Accurate analysis requires well characterized, homogeneous standards with similar chemistry and crystal structure to samples. For oxygen isotope ratios, WiscSIMS has many silicate, carbonate, and oxide standards (Valley & Kita 2009; Page et al., 2010). Other standards exist or are being developed. Potential users should inquire about standard availability.
Use of associated instrumentation at nominal cost can be arranged in support of projects at WiscSIMS including: an Hitachi S3400N Variable Pressure Scanning Electron Microscope with capability for imaging uncoated samples, Electron Back Scatter Diffraction (EBSD), color-filtered CL, EDS, and BSE detectors; a CAMECA SXFiveFE electron microprobe with 5 crystal spectrometers, Field Emission Gun, EDS, CL, and BSE; conventional and laser fluorination stable isotope lab; and a white light optical profilometer.
ANALYTICAL CAPABILITIES FOR WiscSIMS FACILITY USERS:
Currently, the following stable isotope analyses are well-established and routinely available to external users. The beam sizes are typically 10µm and analyses take 3-10min/spot. Mineral analysis is limited by availability of standards. Potential users should inquire about creation of other standards.
Oxygen isotopes (δ18O) with ~10 µm spots:
Zircon, quartz, olivine*, pyroxene*, garnets*, titanite*, calcite*, aragonite, dolomite-ankerite*, magnesite-siderite*, plagioclase*, K-feldspar, spinel*, chromite*, epidote*, opal, coesite, silicate glass*: precision typically ~0.3‰ (2SD)
Carbon isotopes (δ13C) with ~8 µm spots:
Diamond, graphite: precision typically ~0.4‰ (2SD)
Calcite, aragonite, dolomite, ankerite, magnesite-siderite*,: precision typically ~0.7‰ (2SD)
Sulfur isotopes (δ34S) with ~10 µm spots:
Pyrite, anhydrite, pyrrhotite, chalcopyrite: precision typically ~0.4‰ (2SD)
Si isotope (δ30Si) with ~10 µm spots:
Quartz: precision typically ~0.2‰ (2SD)
(*: We request that users obtain EPMA data of individual spots prior to SIMS analyses for correction of matrix effect.)
An analysis with smaller beam sizes down to 2 µm is available for some systems, but analysis is slower (15-30 min/spot) and with degraded precision (~1‰). Other applications with more difficult samples, requiring new standards, or with Li isotopes (δ7Li), Mg three isotopes (δ25Mg, δ26Mg, and excess δ26Mg), oxygen three isotopes (δ18O, δ17O, and Δ17O), and sulfur three and four isotopes (δ33S, δ34S, δ36S, Δ33S, and Δ36S) may also be available. Please contact us for more detailed information.
Note that some samples show an orientation effect and can only be analyzed for isotope ratio by SIMS at reduced precision (Kita et al., 2011). WiscSIMS has detected orientation effects in magnetite, hematite, baddeleyite, rutile, galena, and sphalerite.
WiscSIMS receives a subsidy from NSF/EAR Instrumentation and Facilities Program (link), and external NSF-funded investigators receive priority in allocation of instrument time and are eligible to perform analyses at a subsidized rate. The current subsidized rate is $1,800/day (12 hours), applied to US federally-funded research. The unsubsidized academic rate is $3,600/day (12 hours). Commercial or confidential analysis is also available at a rate of $10,000/day (12 hours).
Analysis of extraterrestrial samples is outside the scope of the NSF/EAR Facility Program. The rate for US federally-funded meteorite research is $2400/day (12 hours) and the unsubsidized academic rate is $3,600/day (12 hours).