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Technology Factsheet

E-Perm Alpha Surface Monitor

Category: Characterization > Monitors > Multipurpose Detectors
Reference # : OST Number 2315, DOE/EM 0534 Model No : E-PERM

The E-PERM alpha monitor is a small, stand alone, integrating electret ionization chamber (EIC) used to measure alpha radiation on all types of surfaces. The electret ionization chamber (EIC) consists of a positively charged piece of Teflon, called the electret, mounted inside a plastic chamber. After the designated exposure time has elapsed, the electret is removed from the chamber. Using an electret charge reader, the electret's final voltage is read. 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. After the charge reader measures the change in the electret voltage, the data are used to calculate the contamination level. Data can be downloaded to a personal computer to provide database and aid in reporting.


-Simple to use and analyze -Semiskilled technician sufficient. -Small size and weight -Unit can be easily located in difficult-to-reach areas -Units can be placed on floors, walls, and ceilings. -Eliminates operator error and fatigue. -Microprocessor collects, stores, and analyzes data to make reporting easier and quicker. -Robust technology. The electrets are unaffected by shock, humidity and temperature. -Capable of measuring very low contamination levels (<10dpm/100cm2)


-Surfaces where the EIC's are places should be relatively flat and smooth to form an enclosed space within the EIC. Gaps between the EIC and surface being monitored may cause erroneous readings. -After the initial electret reading, the final reading of a measurement becomes the initial reading of the next measurement. If the time span between the measurements is lengthy, the electrets may lose voltage charge due to background of other radiation fields and must be re-read before using again. -The electret may attach dust and other small particles that may cause erroneous readings. To remove those particles, dry air or nitrogen should be pressurized to the electret.




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