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Rad Elec prepares to enter
the DOE marketplace

Electret ion chamber senses low levels of alpha radiation
Rad Elec, Inc. of Frederick, Maryland is positioning itself to provide passive alpha detectors for the DOE marketplace. Global Environmental Technology Enterprise (see related article) and Rad Elec have jointly prepared a deployment plan for the company's E-PERM electret ion chamber. The deployment plan defines the DOE market for this technology in terms of anticipated DOE expenditures on site and equipment characterization—$250 to $300 million annually. The plan also estimates that more than 50 percent of DOE sites have a need to quickly and cheaply survey surfaces, soils, debris, and pipes for uranium and plutonium-alpha emitters that are particularly difficult to characterize due to their short range. Performance data contained in the plan were collected during limited demonstrations at Oak Ridge National Laboratory, the Nevada Test Site, Rocky Flats, Fernald, and the Tonopah Test Range.

How it works
E-PERMWhen ionizing alpha radiation from a contaminated surface enters an electret ion chamber through a thin aluminized mylar window, the radiation causes ionization by stripping electrons from atoms of air in the chamber. The ejected electrons are attracted to a positively charged piece of Teflon called the electret inside the E-PERM ion chamber. The electrons collect on the surface of the electret and over time neutralize its charge. After the designated exposure time has elapsed, a technician removes the electret from the chamber. Using a portable, lightweight charge reader, the technician measures the electret's final voltage. The difference in the electret's initial and final voltages is a function of the exposure time and the alpha contamination level to which the chamber has been exposed. After the charge reader measures the change in the electret's voltage, this data can be analyzed with a handheld computer or sent to a PC for calculation of the contamination level.

The small, rugged, lightweight E-PERM electret ion chambers are passive sensors—they need neither power nor batteries. They can be affixed on contaminated walls, ceilings, floors, or equipment and left in place for two to four hours to measure levels as low as free-release limits—1 to 2 disintegrations per minute (dpm) per cm2. They are efficient at detecting alpha radiation and, therefore, suitable for monitoring contamination from uranium, plutonium, and other alpha emitters. A corresponding unit with a window that stops alpha radiation provides background measurement for calculating net alpha radiation.

Several hundred of these detectors can be deployed simultaneously. A technician simply places them at specific test locations and collects them at the end of the desired exposure time, thereby minimizing the time the surveyor is present in the contaminated area.

electretS. K. Dua from Florida International University spoke about the technology at the characterization, monitoring, and sensor technology Crosscutting Program annual review of projects, held in Gaithersburg, Maryland in April 1998. He concluded that the method is suitable for large-scale survey at a cost of less than $5 per measurement.

The baseline method of measuring for alpha contamination is technicians moving alpha-counting survey meters over a surface to scan for radiation. These survey meters and their accessories cost $2,000 to $3,000 each, are relatively heavy but delicate, can become light sensitive, and require skilled technicians. They are difficult to use on large surface areas, such as floors, walls, and ceilings, and in difficult-to-reach places. The handheld meters also require technicians to spend more time in contaminated areas.

The electret ion chamber technology overcomes some of these limitations and is less expensive than alpha-counting survey meters. One charge reader, at a cost of $2,000 to $4,000 depending upon features, can be used with hundreds of reusable chambers, which cost about $40 each. Electrets for insertion inside the reusable chambers cost about $1 per measurement. Factoring in the cost of technicians brings the per-measurement cost to less than $5.

Full-range alpha characterization
The E-PERM electret ion chamber technology can be configured to provide various sensitivities and useful ranges. Various electret thicknesses are available: 1.524 mm (short-term), 0.127 mm (long-term), and specially prepared 4.572 mm. Different chamber volumes can be selected to accommodate probe areas ranging from 50 cm2 to 180 cm2. Another factor in deploying this technology is selecting the exposure time to correspond with the radiation level and the level of accuracy desired.

An OST-sponsored technology
The E-PERM electret ion chamber technology has benefited from the support of DOE's Office of Science and Technology. A cooperative agreement between Rad Elec and Oak Ridge National Laboratory for fiscal years 1994 through 1996 built upon Rad Elec's promising idea of using electrets inside chambers for detecting alpha contamination. Subsequent support through the Federal Energy Technology Center's Industry Programs has helped the technology ready itself for entry into the DOE marketplace. Current issues relate to tailoring the technology for full-scale deployment at a specific DOE site, configuring electret ion chambers for specific alpha sources, and completing protocols for using the E-PERM System in decommissioning and decontamination operations. Rad Elec manufactures the patented sensors and associated instrumentation.

Rad Elec has had commercial success with a similar technology using the same electret ion chambers as sensors—its E-PERM radon monitor. The U.S. Postal Service purchased 20,000 of the company's radon monitors over a three-year period for checking radon levels in its 36,000 post office buildings. The E-PERM radon monitor has a 20 percent market share for indoor radon detectors in the United States and is widely used in Europe and South Africa.

To receive a brochure on Rad Elec's E-PERM System, select it on the Reader Service Card. For more information on this technology, call President Paul Kotrappa at (301) 694-0011, or e-mail him at

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