BRAWM - New air measurements?

We finished counting an air filter for 5/25-5/31 a few days ago, and detected both Cs-134 and Cs-137 at levels that are similar to recent measurements. However, we are starting to think that we might have a very small Cs-137 background line in the lab space we are using which could be the result of contamination by an old experiment. We are now counting a background for several days to see if that is the case. This is going to delay the release of the current data until early next week.

Back in March, we took a background spectrum for about 1 day and we were able to identify non-natural background lines from contamination (Ag-108m and Co-60). Now we are counting samples for nearly 7 days, so that opens up the possibility that there are other lines too weak to see earlier (e.g., Cs-137). So this is also just a prudent thing to do experimentally.

If there is a background line present, this would be creating a systematic increase in the Cs-137 measurements. Once we measure the strength of the line to good precision, we can subtract it off of our other measurements. This would lead to a downward revision of our Cs-137 measurements.

Mark [BRAWM Team Member]