Radon (Rn)
| Atomic number: |
86 |
| Atomic weight: |
[222] |
| Average concentration in ocean: |
3 zmol/kg |
| Residence time: |
5 days |
Distribution in ocean
Radon is present in seawater as the radioactive isotope 222Rn
(half-life of only 3.82 days), which is produced by decay of 226Ra.
222Rn is in secular equiilibrium with its parent isotope except near
the sediments and at the seasurface. An excess
of 222Rn, relative to the activity of 226Ra,
may occur near the sediment-water interface as radon gas diffuses from
sediments, which contain large amounts of radium scavenged from seawater (data).
A deficit of 222Rn is found near the the sea surface as radon gas
diffuses into the atmosphere. The mean radon concentration was
calculated from the mean 226Ra concentration in the ocean and
assuming secular equilibrium. Note: 1 zeptomol
(zmol) = 10-21 mol
Speciation
Radon is dissolved in water as the pure element.
Residence time
The radon residence time is based on the 3.8 day half-life.
Analysis
Radon is stripped from seawater and the decay rate is determined by a-counting.
References & Notes