NukeWorker Forum
Career Path => Radiation Safety => Topic started by: AEROSMITH1970 on Oct 19, 2022, 05:19
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So my company uses a correction factor that basically says 75k dpm is equivalent to 1mR. Our procedure references a pnnl document called "Correction factor to correct ro-20 response to CS-137 activity on a filter". Authored by M.L. Johnson, Pacific Northwest National Laboratory. I have asked other people in my office about this and no one has seen this report or "letter to file" before and to search Google for it and was curious if anyone can point me in the right direction since I'm having no luck.
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https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-14135rev1.pdf
Here is another take by the same guy. Go to page 211 for your thumb rule?
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https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-13603.pdf
This is as close as I could find to your original paper. M. L. Johnson at PNNL was a co-author.
I didn't punch the math, but would guess it comes out to your number?
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I have seen different values used for gamma calibration. However, it depends on the isotopes involved. A 'newer' plant uses Co-60 as the main isotope, for thumb rules. Calibration sources are almost always use Cs-137 due to the 30 year half life. If the calibration source (Cs-137) is > 30 years old, you may need to recertify it and run new calibration curves as it can impact the calibration process. For standard gamma calibration use the Cs-137, others have provided the reference in previous posts.
For conversion for beta included (as in a frisker), it is different.
At a former plant, we did a study and found our conversion factor for friskers should have been around 45000 dpm due to the isotopic mix but were using 100000 dpm that commerical nukes seem to favor.
In operating plants isotopic mixes can change (Co-60 reduction, C0-58 generation, and ingrowth of transuranics from forgotten fuel leaks). As the plant ages, hard to detect can become a significant issue.
In decommissioned plants the gamma goes away, while beta and alpha grows. Harder to detect and calibrate instruments with those changes.
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I have seen different values used for gamma calibration. However, it depends on the isotopes involved. A 'newer' plant uses Co-60 as the main isotope, for thumb rules. Calibration sources are almost always use Cs-137 due to the 30 year half life. If the calibration source (Cs-137) is > 30 years old, you may need to recertify it and run new calibration curves as it can impact the calibration process. For standard gamma calibration use the Cs-137, others have provided the reference in previous posts.
For conversion for beta included (as in a frisker), it is different.
At a former plant, we did a study and found our conversion factor for friskers should have been around 45000 dpm due to the isotopic mix but were using 100000 dpm that commerical nukes seem to favor.
In operating plants isotopic mixes can change (Co-60 reduction, C0-58 generation, and ingrowth of transuranics from forgotten fuel leaks). As the plant ages, hard to detect can become a significant issue.
In decommissioned plants the gamma goes away, while beta and alpha grows. Harder to detect and calibrate instruments with those changes.
Haven't heard Piggyback Beta for a while. Reminder of RadCon growing pains in the 70s. I may be a sick puppy but I kinda miss the wild west nature of those growing pains.