Virtually all SHRIMP RG samples are embedded in 25.4 mm epoxy rounds. Sample preparation is to be done at SUMAC under the supervision of or by SUMAC staff: Improper sample preparation has resulted in many wasted analytical hours. We strongly recommend that users come to the facility at least three days before the start of analytical work to prepare and document samples. If this is not possible, and the SUMAC staff is to make the mount, the specimens and relevant standards should be sent to the Stanford/USGS facility at least two weeks in advance of the users visit.
The SHRIMP RG user fee includes the preparation and documentation of
samples if the user comes to the Stanford/USGS facility to prepare
the sample mount. If sample preparation and documentation is left
solely to SUMAC staff, an extra fee will be charged, the amount of which
is related to the complexity of the mount and whether or not the user provides
the necessary standards.
Sample Preparation FAQ
Sample Types:
Zircon/Monazite/Titanite
(and other small grains)
Up to six 1 cm rows of sample and standard grains are deposited onto and pressed into two-sided tape, covering approximately a 1.5 cm x 1.5 cm square in the center of a 25.4 mm circle. A 25.4 mm (I.D.) cylindrical Teflon mold is positioned so that it surrounds the grains, and a thoroughly blended mixture (25:3 by weight) of Struers EPOES Resin and EPOAR Hardener is poured over them to a depth of 1 – 1.5 cm. The epoxy is left to cure for 12-24 hours. The sample mount is put in a slow (60 °C) oven for about 2 hours and then cooled. The mold is removed. The epoxy plug is trimmed on a lathe to form a disc about 6 mm thick.
The back (non-specimen) side is polished so the specimens can be seen from the back. Finally, the specimen side is polished to expose the individual grains (1500 grit wet/dry sandpaper, followed by 6 µm, then 1 µm diamond powder slurries on a Struers LabPol5 rotary polisher). The sample is ready for documentation (see below).
Prior to placing the mount in the instrument, it is cleaned in a EDTA solution, thoroughly rinsed in de-ionized water and baked in a vacuum
oven for approximately one-half hour.
The sample is then covered with roughly 10 nm of gold in a Denton sputter
coater. The samples can also be easily carbon coated with a carbon evaporation accessory and carbon yarn.
The sample should be no larger than 25.5 mm and no smaller than 24
mm in diameter.
Thickness should not be greater than 6.5mm.
Gold coated specimens being placed into a sample holder.
Larger Specimens
Sample preparation is very similar for the larger samples (e.g., shards of glass, corals). Care must always be taken to place the specimens in the center of the disc, as secondary ion extraction is affected by the edge of the sample holder. This places a 1.5 cm x 1.5 cm limit (roughly speaking) on sample size.
Thin Sections
The general rule of thumb vis à vis thin sections is that they are usually not worth the trouble.
Bitter experience has demonstrated that while it is possible to analyze a standard thin section in the SHRIMP RG, it is not necessarily possible to reproducibly analyze a standard thin section (presumably a result of the highly asymmetric geometry of the thin section adapter used by the SHRIMP RG).
If it is absolutely necessary to use thin sections, provide the SHRIMP RG staff with circular thin sections (25.4 mm diameter) or cut the relevant thin section into rectangles which can then be embedded in epoxy as described above.
1) A classic Leitz petrographic microscope with x50
— x200 magnification using transmitted and reflected light along with a Paxcam digital camera creates images with up to
5120 x 4096 image resolution.
2) Secondary and Backscattered Electron (JEOL 5600LV SEM)
3) Cathodo-luminescence
(JEOL 5600LV SEM with custom Photo Multiplier
Tube assembly)