Radon-222 is a radioactive daughter isotope of Radium-226, which decays
into Polonium-218 and then into other heavy-metal isotopes. 222Rn
is the longest-lived (half-life is 3.82 days) and most-studied isotope
of radon. Because radon is a gas, it will tend to seek a gaseous phase.
Natural radon concentrations in the atmosphere are so low that natural
waters in contact with the atmosphere will continually lose radon by volatilization.
Hence, ground water has a higher concentration of 222Rn than
surface water. Likewise, the saturated zone of a soil frequently has a
higher radon content than the unsaturated zone due to diffusional losses
to the atmosphere.
Radon is typically used in studies of ground water interaction with
streams and rivers because a relatively short residence time in a stream
or river channel will suffice for loss of most of the radon in a parcel
of water. Any significant concentration of radon in a stream or river is
a sensitive indicator of local inputs of ground water. Kraemer and Genereux
(1997) provide a detailed discussion of 222Rn mixing models
and the use of 222Rn to determine areas of ground water discharge
222Rn has also been used in combination with other isotopes
for different applications. Leveque et al. (1971) took advantage of a relationship
between 222Rn and 82Br to investigate zones of permeability.
Sultankhodzev et al. (1971) related 222Rn to uranium decay and
then used He/Rn and Xe/Rn ratios to date ground water.
Source of text: This review was assembled by Eric Caldwell
and Dan Snyder, primarily from Faure (1986).
||Ellins, K.K., Roman-Mas, A. and Lee, R. (1990). "Using 222Rn
to examine groundwater/surface discharge interaction in the Rio Grade,
DeManati, Puerto Rico." J. Hydrol., 115: 319.
||Genereaux, D. P., and Hemond, H. F. (1990). "Naturally occurring
radon 222 as a tracer for streamflow generation: steady state methodology
and field example", Water Resour. Res., 26,, 12, pp.
||Genereaux, D. P., Hemond, H. F., and Mulholland, P. J. (1993). "Use
of radon-222 and calcium as tracers in a three-end-member mixing model
for streamflow generation on the wet fork of Walker Branch watershed",
J. Hydrol., 142, pp.167-211.
||Gudzenko, V. (1992). "Radon in subsurface water studies",
in Isotopes of Noble Gases as Tracers in Environmental Studies; Proceedings
of a Consultants Meeting, International Atomic Energy Agency, Vienna.
||Kraemer, T.F. and Genereux, D.P. (1998). "Applications of Uranium-
and Thorium-Series Radionuclides in Catchment Hydrology Studies."
In: C. Kendall and J.J. McDonnell (Eds.), Isotope
Tracers in Catchment Hydrology, Elsevier, Amsterdam, pp. 679-722.
||Lee, R. and Hollyday, E.F. (1987). "Radon measurement in streams
to determine location and magnitude of ground-water seepage." In:
B. Graves (Ed.), Radon, radium, and other radioactivity in ground water.
Chelsea, Mich., Lewis Publishers, Inc., pp. 241-249.
||Lee, R. and Hollyday, E.F. (1991). "Use of radon measurements in
Carters Creek, Maury County, Tennessee, to determine location and magnitude
of ground-water seepage." In: L.C. Gundersen and R.B. Wanty (Eds.),
Field studies of radon in rocks, soils and water. U.S. Geological
Survey Bulletin, 1991, pp. 237-242.
||Levêque, P. S., Maurin, C., Severac, I. (1971). "Le 222Rn
traceur naturel complementaire en hydrologie souterranie." C. R.
Hebd. Seances Acad. Sci., 272, 18, p. 2290.
||Sultankhodzhaev, A. N., Spiridonov, A. I., Tyminsij, V. G. (1971). "Underground
water's radiogenic and radioactive gas ratios (He/Rn and Xe/Rn) in groundwaters
and their utilization for groundwater age estimation", Uzbek Geol.
J. 5, p. 41.