Distribution in ocean 227Ac (1/2 life = 21.8 years) is a naturally occurring decay product
of 235U. Its immediate parent is 231Pa.
The vertical profile of 227Ac
shows a continuous concentration increase with depth (data).
The activity is near secular equilibrium
with that of 231Pa through the upper 3000 m of the water
column. There is a large excess of 227Ac, relative to the
activity of its parent 231Pa, near the bottom, indicating a benthic
source. Note: 1 zeptomol (zmol) = 10-21
mol.
Speciation
Actinium is present in the +III oxidation state as AcCO3+.
Analysis 227Ac is determined by allowing its daughter 227Th
(half-life 18.7 d) to grow into equilibrium and then determining its activity,
after separating and concentrating Ac from a large volume (~200 L) seawater
sample.