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Can anyone give me some insight (and possible
source documents) into the reasons for the 100cm^2 standard
(or suggestion?) used for removable contamination surveys? Why is it
100cm^2 and not 1,000cm^2, or something smaller or
larger?
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The earliest reference I have seen specifying an area for a smear is "Rules and procedures concerning radioactive substances and associated hazards" by W. H. Sullivan published in 1946. A two square inch paper was wiped over 12 square inches (77 square centimeters). I hate to point this out but there are 12 inches in a foot. This procedure was used at Oak Ridge National Laboratory. By 1954 ORNL has switched to the metric system and an area of 100 square centimeters (Davis et al. "Applied Health Physics Survey Instrumentation" ORNL-332, 1954). Given all the uncertainties associated with smears (wipes, swabs, whatever) 100 is similar enough to what ORNL had been doing, and besides, it was a nice round number. Some sort of standard area was desirable and although it was highly imperfect, it represented a reasonable approach to deal with a difficult problem, assessing removable contamination. At the first meeting of the Health Physics Society in
1955, A. L. Baietti presented a paper "Contamination Levels" that
summarized what was being done at nine major facilities across the U.S. (Health
Physics Conference, June 13, 14, and 15, 1955, Columbus Ohio). The
large majority of the limits for fixed and removable contamination then in use
were specified for a 100 square centimeter area. Some limits were normalized to
1 square centimeter, others used one square foot, and others were for 55 square
centimeters.
Another thing, it was nice to employ the same area
for fixed/total and removable contamination limits. Like today, the detector
areas used back then for evaluating surface contamination varied. But many
detectors had areas very close to 100 square centimeters e.g., the Juno, Samson,
many Poppy probes etc. Larger detector areas were sometimes employed but
the instruments became increasingly awkward to
use.
See also "Use of Smears for Assessing Removable
Contamination," Operational Radiation Safety, May
1999.
Paul Frame
Professional Training
Programs
ORAU
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