RE: Self-Absorption Effects on Air Filters -Reply

[Michael S Ford <MFORD@pantex.com>]

Elizabeth,

A few *quick* comments:

1.  If you find a reference-able number, please let me know.  I have
conducted a fairly extensive literature search with no success.

2.  The numbers Paul cited (30 to 50% self-abs.) are for cellulose
*fiber* filters, not cast membrane MCE filters. In most of the texts I
have read, cast membrane MCE's behave very similarly to
Nuclepores in terms of particle deposition, but you can't say all the
particles deposit *on the surface*.

3.  The MCE filters has been shown to perform the best in terms of
low air flow resistance and low FWHM are the Fluoropores with
polyethylene fiber backing (counting only, won't work in rad chem
procedures).

4.  Based on what I've seen so far, I would latch on to the Reg. Guide
8.21 statement that Paul pointed to (thanks, Paul!).  If we can say that
the Nuclepores have zero self-absorption, then we can safely say
(IMHO) that the cast membrane MCE filters have less than 10%
self-abs.  Note that the RG 8.21 statement does not give you relief in
addressing the filter loading (dust) that is usually more of a concern
than self-absorption. 

v/r
Michael
*************************
Michael S. Ford, CHP
Texas Radiation Advisory Board
Address:
Radiation Safety Department
Battelle Pantex
Amarillo, TX
806.477.5727 phone
806.477.4198 fax
mford@pantex.com
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