Answer to Question #323 Submitted to "Ask the Experts"

Q

What is the collection efficiency for a 2-inch disc smear made of cloth? The cardboard smears where I work have only been assigned a 10 percent collection efficiency.

A

To my knowledge, there are no defined removal efficiencies for swipe materials. Since it isn't possible to predetermine all parameters affecting a given smear sample, or swipe, accurate efficiencies really cannot be known a-priori. Most references that I have seen have tended to assign dry swipe efficiencies in the range of 10 percent to 20 percent when such a value is needed. In my opinion, however, such estimates are speculative. On a related note: Most regulations in the United States concerning transferrable contamination measurements do not require the use of a removable "efficiency." The limits are for the protection of workers and to prevent movement of contamination from within controlled areas. Smears are collected using a specified, repeatable method and the collection efficiency is assumed to be the same as what was used when developing the applicable regulatory limit--or something along that line of thought. Although swipe analysis instrumentation must generally meet precise calibration requirements, final swipe results are qualitative at best. Robert L. Coleman Oak Ridge National Laboratory