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 cell systems are the only way 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
  • We measure: radon - radium - thoron - radon daughters - alpha radiation.
  • The Lucas cell is recognized as the most sensitive and reliable method for these elements.
  • Our instruments are used around the world in exploration for uranium, oil & gas, groundwater and hydrothermal, and in environmental protection, health physics, earthquake prediction, and evaluation of hydrocarbon and NAPL contamination.
  • In the radon business since 1968, our latest major instrument update was 2015.
  • Modern, low-power, field-rugged electronics. Some earlier versions still working after 35 years.
  • Continuous real-time monitoring and data recording.
  • Winter and summer, from the Sahara Desert to the Canadian Shield, our instruments have faced up to severe field conditions.
  • Intrinsically safe functions.
  • Sensitive to geochemical trace levels necessary for radon in lake water and for radon-thoron isotope ratios.
  • Can work in a tent without electricity or be carried from point to point in the field.
  • 50 readings per day. Results available immediately.
  • Rechargeable battery pack good for a long day in the field and recharges in a few hours.
  • Can be operated by junior personnel if carefully supervised.
  • Same instruments used for radon and radium in soil, sediment, plant parts, rocks, water, soil gas, air, and snow, and for radon daughters in air.
  • EPA compliant.
  • Click here for more details of instruments.
  • Click here for or other instruments, components and accessories we provide
  • Technical specification sheets and pictures of our instruments provided on request.
  • Multilingual consulting and training (if required).
For instruments contact
R.H. Morse & Associates Ltd.
skype: robert.morse.toronto

Robert H. Morse, Ph.D., P.Eng.
August 16, 2018
Click here for other applications of our radon instruments.