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Product Comparison: Radon In Water Accessories



For the measurement of radon in groundwater, the RAD7 with RAD H2O accessory is well suited. You take a sample in a 40ml or 250ml vial, or both, depending on the expected radon concentration in the water. This document compares analysis can be made on site or later in the lab. The analysis itself takes 30 minutes and you can analyze one sample per hour. You can have your result within an hour of taking the sample. The RAD H2O has a comfortable operational range of from 400 Bq/m3 in the water to 10,000,000 Bq/m3, or higher concentrations if you delay analysis.


For sea water there are three other accessories. One, the RAD AQUA, needs a bilge or similar pump to deliver water to an exchanger that brings a closed air loop into equilibrium with the water. It gives a fast response (<30 min), continuous measurement of radon concentrations down to 1 Bq/m3 in the water. This is the only system capable of responding to and giving a measure of thoron in the water.

The Radon-in-Water Probe

The Radon-in-Water Probe, a stainless steel wire frame wound with Accurel tubing, also brings a closed air loop into equilibrium with surrounding water. The water around the probe has to be moving, but no water pump is required. The Water Probe has a similar sensitivity to the RAD AQUA but a response time of around 3 hours.

The Big Bottle System

DURRIDGE also offers a Big Bottle System, which analyses water samples larger than the 40ml or 250ml samples used with the RAD H2O. With the larger water samples enabled by the Big Bottle system, it is possible to measure radon concentrations down to less than 40 Bq/m3, which is sensitive enough for coastal waters. The Big Bottle System is available with adopters for 2.5L glass jugs as well as standard plastic soda bottles of sizes ranging from 590ml to 2L (available at any convenience store!). An analysis of a 2.5L sample typically takes about 1.5 hours.

Of all the radon in water accessories, the RAD7 H2O has the highest upper limit of detection. For the other accessories, groundwater radon concentrations may be high enough to pose difficulties. To safely encompass all likely radon concentrations it is best to have the RAD H2O for groundwater and at least one of the three others for sea water.

Application Note: Measuring Radon In Surface and Well Waters

DURRIDGE offers several alternative methods of measuring radon in surface waters, as well as a method for the measurement of piezometer well water. Surface waters generally have radon concentrations below 100 Bq/m3 and often below 50 Bq/m3. Standard methods of measuring radon in water impose a lower limit of 400 Bq/m3 for a marginally precise (±30%) reading. DURRIDGE therefore developed the RAD AQUA, which brings a closed air loop into equilibrium with a continuous flow of sample water, resulting in a lower limit of about 4 Bq/m3 with a precision level of ±5%. For Radon concentrations of 1 Bq/ 3, the level of precision is ±10%.

The intrinsic background of the RAD7 for radon in air measurement is no more than 0.2 Bq/m3. At room temperature this translates to a 0.05 Bq/m3 background radon concentration in the water (this is due to a 4:1 ratio of radon in air to water once it has reached equilibrium). If that value is subtracted as a zero offset, radon-in-water concentrations may be measured down to 0.1 Bq/m3 with ±25% precision. At such low concentrations however it may take a day or more of continuous measurement in order to accumulate the number of counts needed to reach the stated precision level.

For piezometer wells the high-gain, ultra-low concentration limits offered by the RAD AQUA are not needed, and discreet water samples may be preferred over a continuous flow out of the well. For such applications the DURRIDGE RAD H2O works well. With the RAD H2O, samples are taken in 40ml or 250ml vials, and an automated RAD7 analysis may be performed in as little as 30min.

As a compromise, DURRIDGE offers the Big Bottle System, which comes in two flavors, one with a 2.5L glass jug, and another fitting PET plastic soda bottles, which are known to be able to contain radon without loss and which can usually be purchased (full of soda!) in sizes ranging from 350ml to 2L. With 2L soda bottles it is possible to measure radon concentrations down to 40 Bq/m3. For piezometers, 350ml soda bottles are suitable.

Related Products



Water Probe (HTML)

Big Bottle System (HTML)


Price List (HTML)

RAD7 Water Accessories (clockwise from top): RAD H2O, RAD AQUA, Big Bottle System, Radon-In-Water Probe.

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