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Technology Factsheet

E-PERM Electret Ion Chamber

Category: Characterization > Monitors > Radiation Monitors
Reference # : Model No :

The E-PERM Alpha Surface Monitor consists of a small electret ion chamber (EIC), an electret and an electret voltage reader. The EIC is made of electrically conducting plastic. It provides a holder for the electret and a chamber for containing the ions produced by radiation. The electret is a positively charged Teflon disc that serves both as a source of electrostatic field and a sensor. The monitor is stand-alone equipment not requiring any power or batteries. When ionizing alpha radiation from a contaminated surface enters an EIC, the radiation strips electrons from atoms of air in the chamber. The ejected electrons are attracted to the electret, mounted inside the chamber, neutralizing its charge. After designated exposure time has elapsed, the electret is removed from the chamber. The electret’s final voltage is then read through a hand-held voltage reader or a microprocessor reader. The difference in the electret’s initial and final voltages is a function of exposure time and the alpha contamination level to which the unit has been exposed, and is therefore used to calculate the contamination level. The microprocessor can provide immediate contamination level in dpm/100 cm 2 . Data collected through the microprocessor can be downloaded to a personal computer to assist in reporting.


(1) The equipment is small and light. It is easy to setup and operate, and requires no special training. (2) Units can be set in position and left until the exposure time elapses. It minimizes worker’s exposure to radiation and fatigue. (3) The monitors can be set up at difficult-to-access areas. (4) The technology does not create any radiological waste. And (5) the SPER 2 microprocessor collects, stores and analyzes data to make reporting easy and eliminate human error.


technology requires the surface being surveyed to be flat and smooth so that an enclosed space can be formed within the electret ion chamber. Gaps between the EIC and the surface may cause erroneous readings. In addition, the detectors need to be calibrated for high-energy radionuclides before using them for measurement.




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