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Re: Removable Contamination Surveys



Title: Removable Contamination Surveys
We were taught in the US Navy nuke program that the regulation was alpha or beta-gamma contamination/1cm^2. And if you look in the regs that's what it says.
However, the 100 cm^2 became a convention based on the princple background of K40 is around 5  to 50 uuCi/100 cm^2 . A count of 450 uuCi/100cm^2 was 10 to 100 times normal background or 100 cpm above background, with a DT-304 frisker probe at 1/2 inch above the surface, which is where we were told to set our GM detectors to alarm at. This allowed for random fluctuation in background without continuous alarms. This comes from NAVSEA 0989-015 printed in 1975 Rev 4 and first appeared in 1957 in the Navy's RadCon Manual NAVSHIPS 0153.
The motion of the smear as stated by others is based on two fingers pressed together on a smear makes a 1" wide mark. Now if that 1" is dragged over 16" then approx. 100cm^2  has been covered. The 'S' shape was to ensure the area was "averaged", which is not done is a straight line is done.
 
If you look at 49CFR 173.443 a wipe of up to 300cm^2  is permissible.
 
Dan Mackney
Dirrector of Radiochemistry
Wate Stream Technology
----- Original Message -----
Sent: Friday, February 01, 2002 2:50 PM
Subject: Removable Contamination Surveys

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?  Is there anything wrong with increasing the swiped area to increasing the likelihood of detection? 

Specifically, assume a removable contamination limit is set at 200 dpm/100cm^2 for a laboratory and a researcher wishes to use a survey meter to count the swipes.  According to the manufacturer's formula and values (for efficiency of the radionuclide, etc), the meter has an MDA of 400 dpm.  Is there anything wrong with performing the survey over 200 cm^2 so that the detection limit would meet the removable contamination limit?

Thanks,

Pete Jenkins






















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