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No laboratories currently offer 85Kr
analysis as a standard procedure.
is created naturally in the atmosphere when cosmic
rays hit 85Kr.
reaches the earth's surface through precipitation
(as a solute in the rain). This natural cosmogenic
production of 85Kr
is extremely small.
is also created naturally through the spontaneous,
neutron-induced fission of uranium and thorium
in the earth's crust. This production accounts
for an even smaller percentage of the amount of
Atmospheric nuclear testing during the
1940's through 1963 contributed to a significant
increase in the level of atmospheric 85Kr.
But the majority of 85Kr
in the atmosphere and on the earth's surface is
a result of nuclear fuel reprocessing, beginning
in the 1940's. 85Kr
is an abundant fission product of uranium and
plutonium and is released into the atmosphere
during stages of nuclear fuel handling. Because
of this, the 85Kr
activity in the atmosphere has continuously increased
since the 1950's.
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can be measured by through decay counting techniques.
The water sample must be degassed, the Kr separated
and concentrated for analysis. Given the low concentration
a few hundred liters of groundwater are needed
for analysis and counting times of ~1 week are
required for each sample.
can be used to date young groundwater. Due to
the fast decay rate and minimal natural production
in the earth, the absence of 85Kr
verifies that groundwater is older than 1950.
is combined with an additional radioactive isotope
with a similar half-life (such as 3H),
one can gain additional confidence in results.
Under the correct hydrologic conditions (as in
aquifers that have high permeablility or shallow
circulation), isotopes can be used in combination
to trace groundwater flow paths and verify flow
The main disadvantages in using 85Kr
are large sample size requirements and high costs
due to the specialized measurement methods. Its
short half-life and increasing concentrations
in the atmosphere make 85Kr
a potential replacement for 3H
as tritium levels continue to decline.
can be used for dating glacial ice.
by Torsten Lange (University of Freiberg)
for more information on the hydrological uses
can trace the effect atomic facilities have on
the surrounding environment.
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in dating young groundwater: chlorofluorocarbons,
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on water regimes and transport processes of
substances in waste and mining dumps and natural
aquifers by environmental isotopes - applying
as an alternative isotope in hydrogeology.
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