Rodon Measurement System

Electronic radon detector with real-time monitoring and spectral analysis

The DURRIDGE RAD7 is a truly versatile radon detector of mature and yet still state-of-the-art design. Its specifications match or exceed those of the most expensive radon measurement devices in the world. At the same time, it incorporates a number of exclusive features that are found in no other radon detector, regardless of price. Incredibly, the RAD7 is affordable.

The RAD7 is a sophisticated measuring instrument widely used in laboratories and research work around the globe, by radon testers, mitigators and home inspectors, in mines and deserts, on the ocean and up volcanoes, at extremes of temperature.

The RAD7 is also the simplest computer-driven electronic detector to use, with pre-programmed set-ups for common tasks. It’s built to withstand everyday use in the field. A rugged, handsome case encloses the detector, which is self-contained and self-sufficient. The RAD7 comes complete, with a built-in air pump, rechargeable batteries, and a wireless infrared printer. The printer can be left in your office or your car, when desired, and the detector will collect data and store it for later printing or downloading to a PC.

The RAD7 is a Sniffer that uses the 3-minute alpha decay of a radon daughter, without interference from other radiations, and the instantaneous alpha decay of a thoron daughter. The RAD7 sniffs out entry points and radon gushers and recovers in minutes from high radon exposures. The RAD7 is also a Continuous Monitor that measures the EPA action level of 4 pCi/L, with 10% standard deviation, in one hour. At the end of each run, the detector prints out a complete report.

Radon In Water Accessory for the RAD7

The RAD H20 is an accessory for the RAD7 that enables you to measure radon in water over a concentration range of from less than 10 pCi/L to greater than 105pCi/L. By diluting your sample, or by waiting for sample decay, you can extend the upper range to any concentration.

The equipment is portable and battery operated, and the measurement is fast. You can have an accurate reading of radon in water within an hour of taking the sample. The RAD H20 gives results after 30 minutes analysis with a sensitivity that matches or exceeds that of liquid scintillation methods. The method is simple and straightforward. There are no harmful chemicals to use. Once the procedure becomes familiar and well understood it will produce accurate results with minimal effort.

By taking two simultaneous samples, analyzing one immediately, waiting a week or more and then analyzing the other, the radium (226Ra) content of the water may be calculated.

Continuous Radon in Water Accessory for RAD7

The RAD AQUA is an accessory for the DURRIDGE RAD7 radon detector that is used to bring the radon concentration in a closed air loop into equilibrium with the radon concentration in a flow-through water supply. It consists of a spray chamber, called an “exchanger”, that brings the air and water into equilibrium. The radon in the air is monitored continuously by the RAD7.

The partition coefficient (the ratio of radon concentration in the water to that in the air at equilibrium) is determined by the temperature at the air/water interface. This temperature is measured with a temperature probe inserted into the exchanger. At typical room temperature the coefficient is about 0.25. That means the concentration of radon in the air is four times higher than in the water. As a result, the system’s sensitivity to radon in water is four times higher than the sensitivity to radon in air.

It takes time for the water to deliver radon to the air loop and for the RAD7 to respond to the changed radon concentration. With optimum configuration the response time of the system may be reduced to less than half an hour.

Water Probe
Slow Response Monitoring of Radon in Water

The DURRIDGE Water Probe is used to collect radon samples from large bodies of water. The probe consists of a semi-permeable membrane tube mounted on an open wire frame. The tube is placed in a closed loop with the RAD7.

When the probe is lowered into water, radon passes through the membrane until the radon concentration in the air in the loop is in equilibrium with the water. The equilibrium ratio of radon in the air to radon in the water is determined by the temperature, which must be measured.

The probe has the same high sensitivity as the RAD AQUA. As such it can be used to monitor the radon concentration at a specified depth in open water. The probe has an advantage in that it does not need a pump for the water. It will, however, take more than two hours to make a spot measurement or to respond to a step-change in radon concentration. It is important that there be some flow of water around and through the device as it will remove radon from the water in its vicinity as the radon passes into the membrane tubing.

To monitor a water supply, the probe may be placed in a container with the incoming water released at the bottom of the container and overflowing or exiting through an outlet at the top. The water in the container should be completely refreshed with incoming water at least twice an hour.

Soil Gas Probe In-Ground Radon Detection

When measuring radon underground, it is essential to collect samples without exposing them to the outside air. DURRIDGE offers two heavy-duty soil probes for this purpose: the durable and easy to use AMS Stainless Steel Soil Gas Probe, and the regular Steel Soil Gas Probe.

Designed to be simple and effective, DURRIDGE’s Soil Gas Probes consist of a hollow steel tube with a collar and NPT thread at the top. An included drive rod slides down the inside of the tube and penetrates the ground. Also supplied with the probe is a pilot solid steel rod 3/8” diameter to make a pilot hole for the probe.

The only necessary equipment, besides the RAD7 itself, is a self-grip wrench, a 5/8″ open or adjustable wrench, hammer and teflon tape.

DRYSTIK Humidity Exchanger to Extend Desiccant Life Span

The DURRIDGE DRYSTIK transfers humidity in incoming air to the stream of dry air being pumped out of the RAD7. This means that any air being sent through a drying unit on its way to the RAD7 will have already lost most of its moisture, greatly extending the life of the desiccant in the drying unit.

The DURRIDGE DRYSTIK is available in two models: the Active DRYSTIK and the Passive DRYSTIK. The Active model comes bundled in an enclosure containing a built-in pump, while the Passive model relies exclusively on the RAD7’s internal pump. Each model is available with three lengths of tubing, with the greater lengths permitting increased preservation of desiccant.

In typical conditions, the 12″ Passive DRYSTIK will preserve a container of desiccant for two months of continuous use, a significant improvement over its standard useful life span of 10 days. The 48″ Active DRYSTIK, by comparison, will preserve the desiccant for over three months. DURRIDGE also offers a premium 144″ option.

Both the Passive and the Active DRYSTIK models operate on a principle involving two tubes, one inside the other. The inner tube is made of NAFION, a Teflon based material that permits the movement of water molecules, while blocking air and radon. The air sample flows along the inner tube on its way to a drying unit (not included), while the space around the inner tube is purged with dry air coming from the outlet of the RAD7.

Duty Cycle Controller Accessory for Active DRYSTIK and Soil Probe

Monitoring soil gas in the long term, for geotechnical and earthquake studies, is likely to dilute the soil gas sample with fresh air diffused down from the surface. The DURRIDGE Duty Cycle Controller can control the 12V supply to an Active DRYSTIK, with a duty cycle anywhere from 100% to less than 1%. This means that the average flow rate can be carefully controlled to eliminate dilution of the sample and enable soil gas sampling to continue indefinitely.

Range Extender

Increase the range of the RAD7 in high radon areas

The Range Extender mixes fresh air with sample air to reduce the concentration of radon in the air fed to the RAD7 radon detector by an order of a magnitude, greatly increasing its effective range.

The extender consists of two parallel capillary tubes joined at one end to the outlet hose connector. Fresh air is fed to the input of one tube while the incident radon sample is fed to the other. A differential pressure sensor across the two tube inputs, with a needle valve for adjustment, is used to ensure that both capillary tubes have the same pressure drop across them.

With this system the radon concentration delivered to the RAD7 will be reduced by a factor of 10:1 regardless of the strength and flow velocity of the RAD7 pump. The pump can cycle on and off without affecting the reduction factor.

The Range Extender can be used for the measurement of very high radon concentrations in air, in soil gas and in water. It can also be used with any other instrument that has its own pump, for any gas. If used to extend the range of thoron measurement care must be taken to assess and correct for the additional decay of the thoron due to sample acquisition delay.

Emission Chambers

Soil and Hard surface emission detection

Two emission chamber accessories are offered for the RAD7 radon detector: one for soil surfaces and one for hard surfaces. The Soil Surface Emission Chamber has a stainless steel skirt around the circumference, to penetrate the soil. The Hard Surface Emission chamber has a flat base with sealant.

For soil emission measurements, the skirted chamber may be placed on the ground and stood upon, to push the steel skirt into the dirt. A closed loop measurement may be completed in approximately 30 minutes. Open loop monitoring may be performed continuously, showing diurnal variation of soil emission and allowing the user to obtain as high a precision as desired.

For hard surface emission measurements, the chamber without the metal skirt, and with a soft seal instead, may be applied to the surface. Closed and open loop measurements may be made.

Closed loop protocol provides a quick and sensitive reading, while open loop offers increased scope for investigating variations in emission due to changes in parameters such as barometric pressure, temperature, relative.