Distribution in ocean
Radium is a naturally occurring radioactive element. The major isotope, 226Ra
(half-life 1622 years), is produced by the decay of 230Th.
Thorium is very particle reactive and it is rapidly transported to marine
sediments. The radium profile
has a strong benthic source with high concentrations near the bottom (data).
Speciation
Radium is present in seawater as the Ra2+ ion.
Analysis 226Radium is determined by stripping 222Rn, it's daughter
product, from seawater and then measuring the ingrowth of 222Rn.