I need to digest solid sapphire chunks (100-500 mg) in order to measure the Th and U content...with part-per-trillion detection limits. The material is being considered for ultralow background physics detectors (think dark matter).
We have both CEM and Milestone microwave digestion systems. They can both get up to 270C, or so, for upwards of an hour. Can you recommend a digestion recipe? We've heard that 4 mL con sulfuric, 4 mL con phosphoric, and 1 mL con HF works at high temp, but the reaction is ridiculously slow. And the phosphoric acid is very contaminated with U and Th (and pretty much any other metal, I presume, as it is not distillable). Are there any other ideas out there? We fear any sort of fusion will not provide adequate sensitivity levels to be interrogated (lots of background contamination).
In order to increase reaction kinetics, we could grind the sample up to a fine powder. Thus, grinding/milling processes will most likely contaminate the sample, and leaves us scratching our heads in terms of what to do about process blanks. Any ideas on how to CLEANLY pulverize sapphire (it is the second hardest material on earth)?
Isaac J. Arnquist, Ph.D.
Radiation Imaging and Material Sciences
Pacific Northwest National Laboratory
902 Battelle Boulevard
P.O. Box 999, MSIN J4-70
Richland, WA 99352 USA
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