...during recent cavity decon at lasalle worker was told 120 nCi intake Co60 only, 10 mR, week to clear...
...my personal experience, 80 nCi intake Co60 only, took a year to go non-detectable (10 nCi) by fastscan...
...Co60 bio T1/2 is 9.5 d so effective T1/2 has to be less...
...from 120 nCi to 7.5 nCi, 4 bio T1/2's is roughly 40 days...
...why was the worker told a week when it looks like it should have been more than a month...
...why was i detectable (>10 nCi) by fastscan for a year when it looks like it should have been less than a month...
My guess would be the location & chemical form of the Co-60.
Soluble would have the 9.5 day biological halflife you are quoting.
If it was insoluble & got into the GI tract, it would easily pass in less than a week. This has been my experience with the internal exposures I have received. A couple of days of not being able to clear the portals...then home free. (My highest was 271 nCi mixed activation isotopes at WNP-2. They gave the whole cavity decon crew 'Get-Out-of-Jail-Free' cards for the PCMs so we could still work in the RCA.)
If the isotope was an insoluble form that got lodged in the lungs, then a longer retention time (as in your case, Bill) makes sense.
So, for the La Salle worker, I have 2 thoughts. Either:
1. The person saying a week didn't understand halflife...and just quoted 9.5 days as the total time...
or
2. The person saying a week had good historical perspective on how La Salle
uptakes intakes clear themselves and knew that most of the Co-60 would just pass through, so was confident saying it'd all be over in less than 7 days.
Does that match your thoughts?