The determination of filter efficiency and fraction separation efficiencies for size ranges < 300 nm is performed, among other means, by using electrical mobility classifiers (e.g. DEMC 2000) to provide particles of different sizes.

This involves applying a charge to the aerosol for functional reasons. As improved deposition on the filter can be attained with a charged aerosol than with an uncharged aerosol, the EN 1822 standard favors neutralizing the aerosol upstream of the filter.
Radioactive emitters, such as krypton 85, are established in practice for this purpose. The use of these emitters entails a good deal of bureaucracy and special safety measures are necessary. A handling permit has to be applied for and a radiation protection officer has to be nominated. Special training is also required, safe storage of the emitter has to be ensured, and more besides.

The Palas^® engineer Mara Pfeffinger therefore investigated whether in filter testing with the MFP Nano plus test rig, instead of using a radioactive emitter, an X-ray emitter can also be used for neutralization of the aerosol. As they are uncomplicated, they are already widely used. It should also be investigated whether an X-ray emitter achieves the same performance in determining the filter efficiency and MPPS (most penetrating particle size) in the nanometer range as a radioactive emitter.

Figure: Palas^® investigation on neutralization of aerosols in filter testing with a radioactive emitter and a X-ray source

Mrs. Pfeffinger made measurements with the MFP Nano plus test rig with different filter media, both with the krypton emitter Kr-85-370, as well as with the X-ray emitter XRC 049 from Palas^®. The result of the measurement series was that only very minor differences were to be ascertained between the two emitters. These were within the variability of the filter medium. “Further measurements need to be made with different filter media and settings to be absolutely sure, but to a first approximation it can be said that an X-ray emitter can also be used to neutralize the aerosol”, Mara Pfeffinger takes initial stock of her investigations.

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