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Radon Monitoring in Air, Water, Soil and Flux

Radon in Air 

The E-PERM® is a patented passive radon monitor listed as approved by most certifying agencies. This device is very widely used in more than 30 countries and is listed as the most used device in the USA for long and short term radon measurement. Only radon gas, not radon decay products, diffuses through the filtered inlet into the chamber volume until the concentration of radon inside the chamber is the same as that in the room.  Radiation emitted by the decay of the radon and the decay products formed inside the chamber ionizes the air.  The positively charged electret attracts the negative ions generated by the radiation in the chamber resulting in a net decrease of the electret voltage.  Positive ions go to the wall of the chamber and get dissipated.  This voltage decrease of the electret is proportional to the radon concentration and the time of the exposure.  The drop in voltage of the electret is a measure of the product of the radon concentration and the exposure time given in; (pCi/L)-days or Bq/m3 –days. Different combination of volumes and electrets covers virtually all the ranges of interest in scientific and professional fields.   

The components needed for testing are: electret, chamber, electret reader and software for data reduction. The conveniently packaged and affordable “Starter Kit” comes with all that is needed for any beginner user. The Starter Kit also provides a training DVD. 

These monitors are not affected by varying concentration, temperatures or humidities and are therefore excellent for use in a variety of applications which include basic research, health related measurements, indoor and outdoor radon measurements, and uranium exploration projects.

Figure 1 gives the components of E-PERM® System, Figure 2 gives different chambers and Fig 3 gives the on/off mechanism for S chamber. This on/off mechanism is very important and helps in shipping from one place to another without picking up any signal.

The following list of publications provides additional information on the technology and inter-comparison with other devices:

  • Kotrappa, P., Dempsey, J.C., Hickey, J.R., and Stieff, L.R., "An Electret Passive Environmental Radon Monitor Based On Ionization Measurement" Health Physics 54; 47-56 (1988)
  • Kotrappa, P., Dempsey, J.C., Stieff, L.R., and Ramsey, R.W., "A Practical Electret Passive Environmental Radon Monitor For Indoor Radon Measurements" Health Physics 58; 461-467 (1990)
  • P.Kotrappa and L.R.Stieff "Elevation Correction Factors for E-PERM® radon Monitors" Health Physics 62; 82-86 (1992)
  • Kainan Sun, R.W. Field "Comparison of Commercially available Short Term Radon Monitors" Health Physics 91; 221-226, 2007
  • A.Vargas and X.Ortega "Influence of Environmental Changes on Integrating Radon Detectors: Results of an Inter comparison Exercise" Radiation Protection Dosimetry 123:529-536 (2007)

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  Radon in Water 

A small water sample is placed in the bottom of a glass jar.  An E-PERM® radon monitor is suspended in the air phase above the water. The lid of the flask is closed and sealed to make it radon-tight. Radon reaches equilibrium between the water and air phase.  At the end of the desired exposure period, the flask is opened and the E-PERM® removed.  The average radon concentration in the air phase is calculated using the standard E-PERM® procedure.  A calculation using this air concentration in conjunction with the other parameters gives the radon concentration of the water. A user friendly kit with instruction manual and template is provided for the users.

Following publication gives details of the method and also the inter-comparison of results with other methods:

  • Kotrappa. P., and Jester, W.A., "Electret Ion Chamber Radon Monitors Measure Radon In Water" Health Physics 64; 397-405(1993)
  • Gregory Budd and Craig Buntley "Operational Evaluation of the electret ion chamber method for determining radon in water concentrations" 1993 International Radon Conference AARST 1993  hosted by AARST (EPA reviewed paper)
  • P. Kotrappa and W. A. Jester, "Electret Ion Chamber Radon Monitors Measure Dissolved 222Rn in Water" Health Physics 64;397-405 (1993).

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Radium Concentration in Soil

The procedure for measuring radium in soil is similar to that used for measuring radon in water.

A soil sample, weighing about 30 grams, is dried and humidified with 30% moisture. It is placed in a Petri dish and lowered to the bottom of the analysis bottle. An E-PERM® is suspended from the top of the lid. Radon emanated from the sample accumulates for a period from 5 to 15 days. At the end of the exposure period, the E-PERM® is taken out and the average radon concentration is calculated.

Using this information it is possible to calculate the radium concentration by assuming an emanation coefficient of 0.25. This coefficient is usually valid for most soils. The manual contains exact equations in a convenient form for the user.  

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Radon Flux from Ground, Soils, Surfaces and from Building Materials

There are several applications for procedure. These include:

  1. Measuring radon flux from the uranium mill tailings
  2. Estimating indoor radon potential of building sites
  3. Uranium prospecting
  4. Radon emanation from objects and building materials

The E-PERM® H chamber is modified to feature a large, carbon coated Tyvek® diffusion window. The chamber is vented by filtered outlets so that it will not accumulate radon. When the E-PERM® flux monitor is placed on radon emanating surface, the radon enters through the Tyvek® barrier and exits through the vents. The semi-equilibrium radon concentration established inside the chamber is representative of dynamic flux from the surface. Because of the equilibrium between the ground and outside environment through vents, the flux emanation from the ground is not disturbed.  These have a stainless steel collar that can be used to anchor them to the ground. The electret discharge rate of the electret is a measure of the radon flux. E-PERM® flux monitors are calibrated on the well-characterized radon flux beds at CANMET (Canada). These flux beds consist of 226Ra bearing material (well-characterized uranium tailings) 5.5 cm thick and 5 meter in diameter. The bed is precisely characterized by CANMET to provide a radon flux of 7.7 ± 1.1 pCi m2 sec-1 ( 7.7 flux units).

 To measure Radon emanation rates from objects and building materials), the object is enclosed in an accumulator along with the E-PERM® radon monitor. REI provides appropriate analytical tools to calculate such radon emanation rates.

  • Kotrappa, P., Stieff, L.R., and Bigu, J., "Passive E-PERM Radon Flux Monitors For Measuring Undisturbed Radon Flux from the Ground" 1996 International Radon Symposium AARST (1996)
  • Jack Rechcigl et al "A preliminary comparison of radon flux measurements using large area activated charcoal canister (LAACC) and Electret ion chambers (EIC) 1996 International Radon Symposium,  AARST 1996
  • P.Kotrappa" Radon emanating radium concentration from soil" E-PERM Manual 2007
  • J.Charlton and P.Kotrappa  "Uranium Prospecting for accurate time-efficient surveys of radon emissions in air and in water, with comparisons to earlier radon and He surveys"  Kotrappa  Proceedings of International Radon Conference  AARST 2006


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Residential Testing
Radon & Radon Decay Products
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