Laboratory
Background The
National Ion Microprobe Facility is collection of faculty, students, and
researchers engaged in various geo- and cosmochemical fields of study.
The group is headed by Professors Kevin
McKeegan, Mark
Harrison, and Mary
Reid of UCLA's Department
of Earth and Space Sciences (ESS) and Institute
of Geophysics and Planetary Physics (IGPP). The principal resource
of the W.M. Keck Foundation Center for Isotope Geochemistry is a CAMECA
ims 1270 high resolution, high sensitivity ion microprobe. The Division
of Earth Sciences of the National Science Foundation provides a portion
of the support for the Keck Center to enable us to host external users
from the geological and related communities. We seek to provide the user
with a world-class instrument that is developed to support applications
that both take advantage of its unique capabilities and are at the forefront
of scientific investigations.
| For Further Information Please Contact: | ||
| Kevin McKeegan | kdm@ess.ucla.edu | (310) 825-3580 |
| Marty Grove | marty@argon.ucla.edu | (310) 825-7975 |
| Mary Reid | reid@zephyr.ess.ucla.edu | (310) 825-1756 |
| Chris Coath | coath@argon.ucla.edu | (310) 825-2719 |
| IonProbe lab | (310) 825-4328 | |
Instrument
Description The UCLA Cameca ims
1270 is a new generation, high-resolution / high-sensitivity ion microprobe
(or Secondary Ion Mass Spectrometer: SIMS) designed specifically for microscale
isotopic and elemental analysis of complex minerals. It is an extremely
versatile tool, capable of analyzing either conducting or insulating samples
for elements ranging from H through U. For
the following discussion consult the plan view
of the Cameca ims 1270. The instrument is equipped with both Cs+ and duoplasmatron
(16O-) primary ion sources which can be focussed to produce ion beams as
small as 1 mm diameter, although ~10 mm sputter craters are more typical
for isotopic analyses. A large-radius triple-focusing mass spectrometer
maintains high transmission even at the high mass resolving power (MRP
~ 6,000) required for Pb isotopic analysis of zircon. As with other Cameca
ims instruments, the 1270 also functions as an ion microscope by direct
ion imaging of the sample (with ~0.5 mmlateral resolution), enabling precise
location of small inclusions for isotopic analysis (e.g., microfossils).
A normal incidence electron flood gun provides charge compensation which
enables analysis of electonegative elements (e.g, carbon and oxygen isotopic
ratios) in thin-sectioned samples of (electrically insulating) rocks. Isotope
ratios are measured either by rapid field switching with a laminated magnet,
or by simultaneous multiple collection of up to 5 ion beams. The forward
geometry design of the mass spectrometer enables energy filtering as well
as multiple isotope collection. The multiple collection may be achieved
with either Faraday cup detectors, or with discrete dynode electron multipliers
for ion counting applications. Low (2000), moderate (4000), or high (6000)
mass resolution modes are available in multicollection, whereas continously
variable MRP (~1000 to ~15000) may be achieved with the off-axis monocollector.
Isotopic precision achieved is typically in the range of 1 permil but is
highly sample and element dependent: see specific application notes.
