The SHRIMP II was designed with stable isotope analysis as a
prime motivation. However, owing to a number of competing instrument
developments (multiple collection, SHRIMP RG) the stable isotope
work was not actively pursued. Furthermore, stable isotopes are
best analysed as negative ions with optimum ion yields from a
Cs+ primary beam requiring a polarity change from the configuration
for positive ion analysis used in U-Pb.
The SHRIMP SI is designed with careful attention paid to the
ultimate vacuum in the source chamber, and to the use of standard
ETP multipliers in the multiple collector. Laser illumination
will be used to assist in removing contaminants from around the
sputtered region. These features are important for accurate measurements
of extraterrestrial materials being collected from the Genesis
and Stardust missions.
At this stage detailed drawings are being made for the SHRIMP
SI with a view to commencing construction in 2006.
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