1 ES 6216 – Isotope Geochemistry Problem Set 2 Distributed 9/11 ...

) Assuming that no Th was incorporated into its skeleton when it precipitated, how
many 230 Th atoms does a 1g sample of this coral contain?
c) The analytical precision for a U-Th age is typically limited by measurement of the
230 Th atoms, and typically one is lucky to recover 0.05% of the total 230 Th atoms during
a typical mass spec run. What will be a minimum 2σ relative error on the U-Th age for
your 1g coral sample?
7. Suppose a radioactive gaseous element in the atmosphere has a half-life of 6yrs. Its daughter,
also radioactive, has a half-life of one month. Because the daughter is not gaseous, it adsorbs
onto aerosol particles and is removed by physical processes, mainly precipitation. If the
activity ratio for these two isotopes (daughter/parent) in the atmosphere is observed to be 0.3
in steady state, what is the lifetime of the daughter with respect to physical removal from the
atmosphere?
8. The following activity ratios were measured in a manganese nodule. Estimate the growth rate
of the nodule, assuming that the amount of U-supported 230 Th is negligible.
Depth (mm)
230 Th/ 232 Th
0-0.3 43.7± 1.8
0.3-0.5 26.2 ± 0.6
0.5-0.85 10.4 ± 0.3
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