Some
notes on the geochemistry of radon and radium applied to uranium exploration
·
Radon
and radium occur about midway in the uranium decay series.
·
Once
separated from the parent uranium it takes a million years for radon and radium
to grow back into equilibrium with uranium. Therefore, any correlation with
uranium in younger material is due to similar chemistry, not radioactive
production.
·
The
parent-daughter pair radium-radon grow into equilibrium with the half-life of
the daughter radon, 3.8 days. This provides the classic and EPA technique for
radium analysis: let the radon grow into equilibrium with radium and then
measure the radon with the Lucas cell.
·
Radon
is soluble in water and, given the extremely low abundance of radon in the
earth (due to its short half-life), water is never saturated with radon and
radon bubbles never form; however, if another gas phase is present radon will
enter the gas phase according to Henry’s law.
·
With
half-lives of 3.8 days and 1,622 years respectively all the radon and radium in
the earth came from radioactive decay of uranium or thorium. Therefore, there
is no reason to suggest that radon and radium are any less direct than uranium
as geochemical indicators of uranium ore.
·
In
some cases radium is a more direct indicator than uranium because in the
surficial environment uranium is more likely to be enriched by organic matter
in sediments and soils leading to false anomalies.
·
Variations
in radon content on a day-to-day or hour-to-hour basis can be smoothed out by
repeated readings.
·
Radon
does not come out of solid rock. A radon anomaly in soil gas cannot be
explained by the proximity of granite or pegmatite boulders. Likewise, although
radon can be detected in snow overlying frozen clay-rich soil it cannot be
detected in snow overlying highly radioactive bare rock.
·
Variations
of content of the two main isotopes of radon, radon-222 and radon-220 (thoron),
with half-lives of 3.8 days and 55 seconds respectively, reflect soil
permeability and can be used to fine tune the results and weed out false soil-gas
anomalies. Of all the radon measuring instruments and techniques Lucas cells
provide the only method of resolving these two isotopes. The gamma-ray
spectrometer will not do it.
·
Radon
results are available in five minutes in the field for immediate follow-up.
·
For
more details on principles see
www.finderschoice.com/radon/principles.php
.
For instruments contact: 1-416-269-9979 morse@finderschoice.com
Copyright 1968 - 2018, R.H. Morse & Associates Ltd., all
rights reserved.