BRAWM Air Reports Vs. Calif. Dept Of Public Health
I'd like the BRAWM teams thoughts on the CDPH reports mentioned
below.
Three questions:
1. Why were the CDPH results much higher in the majority of the
reports?
2. How many years would you have to breath the air for say the
1.55 pCi/M^3 result (which is 13x the BRAWM high) to equal the
cross country flight?
3. In general, how does the BRAWM team feel about the CDPH results?
I brought this up a while ago, but I just wanted to bring it up
again since I have some additional info. Tim originally thought
there was a typo in the CDPH report because the raw data. But,
there was another result of 0.90 pCi/M^3 by itself in the next page.
Original post: http://www.nuc.berkeley.edu/node/3502
The highest reported level from the BRAWM team for I-131, was from the
3/23 18:13 to 3/24 18:02 sample. That was 4.3E-6 Bq/L or 0.12 pCi/M^3).
The Calif. Dept. of Public Health reported the following I-131 detections
in their March 25, 2011 report:
http://www.cdph.ca.gov/programs/Documents/CDPH-RHB-RadReport-2011-03-25.pdf
Eureka 3/20/2011 0.49 pCi/M^3 (1.81E-5 Bq/L)
Richmond 3/20/2011 0.09 pCi/M^3 (3.33E-6 Bq/L)
Livermore 3/21/2011 1.20 pCi/M^3 (4.44E-5 Bq/L)
Avila Beach 3/20/2011 1.45 pCi/M^3 (5.37E-5 Bq/L)
San Luis Obispo 3/20/2011 1.55 pCi/M^3 (5.74E-5 Bq/L)
Los Angeles 3/21/2011 1.00 pCi/M^3 (3.70E-5 Bq/L)
San Diego 3/21/2011 1.26 pCi/M^3 (4.67E-5 Bq/L)
The BRAWM team reported:
3/19/2011 21:13 to 3/20/2011 09:24: 3.3e-06 Bq/L
3/20 08:30-18:45: 8.3e-07 Bq/L
The 3/19-3/20 report is very close to the CDPH report for Richmond, Ca,
which is the closest to Berkeley.
However, the CDPH also reported an I-131 level of 1.11 pCi/M^3 (4.11E-5
Bq/L) in Richmond, Ca. on 3/24.
http://www.cdph.ca.gov/programs/Documents/CDPH-RHB-RadReport-2011-03-28.pdf
That is the same day that the BRAWM team reported it's high of
4.3E-6 Bq/L or 0.12 pCi/M^3. But, the CDPH result is over 9 times
higher.
Cross-calibration is difficult
Making sure that two different systems measuring the same thing get the same answer is a big deal in science. But it's also a big pain in the neck, since no two systems are alike. At this point, there are things that need to be recalibrated in our system as we refine our measurements, but we also don't have a good idea of what sorts of methods CDPH is using.
A longer explanation of these points:
(1) We are soon going to recalibrate our air system. We did a quick calibration of our air filter geometry when we started back in March, but we have learned so much more since then about how to work with our system. This and any other refinements we do could affect our numbers. However, I don't think we would be more than a factor of 10 away from the absolute activity concentration in the air.
(2) We don't know all the details of the CDPH testing. For example, we don't know what kind of air filters they are using, what kind of airflow they are getting, what kind of gamma-ray detectors they are using, how they calibrate those detectors, and how they calibrate their filter geometry. I'm not saying they are incomplete in how they report their results; it's just that so many technical details go into the final number that we just have no way of knowing where the discrepancy could lie. If anyone finds some of those details, that could be helpful -- but even that probably won't give the answer without a lot of study.
By the way, the answer to question #2 from the OP: If their number is 13 times higher than our number, then just take our "years to breathe the air" and divide by 13. So for our peak number of 4.3E-6 for I-131, we say that it would take 170 years to breathe the air with that concentration to get the equivalent of a plane flight. If you instead use the CDPH number, you get 5.7 years. Let me also note that these are the very highest values for both our results and CDPH, and one would never be able to breathe air at that concentration for even a single day, let alone years.
Mark [BRAWM Team Member]
Factor of 10?
Hi Mark,
"I don't think we would be more than a factor of 10 away from the absolute activity concentration in the air"
Meaning that your peak I-131 result of 4.3E-6 could have been at a time
when the absolute activity concentration was actually 4.3E-5? If so, that
would put the BRAWM number close to what CDPH reported for Richmond and
Livermore at that time.
Also, I've been told that AIR-CHARCOAL sampling can increase results
by a factor of 10 over AIR-FILTER sampling. Is that true?
Based on a comparison we
Based on a comparison we made between our standard HEPA filters and a hybrid HEPA/activated charcoal filter that we constructed, there is not a large gain from using activated charcoal. We found about an 80% increase in the activities in the charcoal+HEPA arrangement over the 0.3 micron HEPA alone. So this led us to conclude that it would not be a factor of 10 increase. We had heard early on that it could be that large, but it might not be the case for us.
So at least in our case, the filter type may increase the numbers by 80%, or a factor of almost 2. The other source of uncertainty is our efficiency calibration, which we are going to re-do soon. A revised efficiency calibration could change the numbers by a factor of maybe 2 -- either higher or lower. That's a very rough estimate though. So my earlier factor of ten might be overstating things -- we're probably pretty close to the absolute number.
Mark [BRAWM Team Member]
Will the numbers reported be updated?
Thanks, Mark!!!
Will the numbers already reported be updated to reflect these changes?
Yes, and we'll describe the
Yes, and we'll describe the changes when it happens. Recalibration will take a couple weeks probably...
Mark [BRAWM Team Member]
Really, really appreciate the transparency!
Really, really appreciate the continuing transparency, detailed explanations, and diligence / faithfulness, Mark, and the entire BRAWM / UCBNE team! ...Just figured I'd say that here, in case you all had missed the other 794 times I'd posted words to that effect. [Grin] Y'all're the best!
Rick Cromack.
Allen, Texas
Ditto!!!
I'm the OP. And I too really appreciate the transparency. I've learned
a lot through our exchanges.
THANKS!!!
Mark, I'd be interested to
Mark, I'd be interested to hear your comments to this post.
Thanks.
BRAWM's calculations agree
BRAWM's calculations agree favorably with the CTBTO monitor in Sacramento, for Iodine and Cesium.
Thanks, Mark!!!
Thanks for responding Mark. I really appreciate it.
I'll see if I can get some of the info from CDPH that you mentioned.
If not to dig into the differences in results, at least just FYI.
Thanks again!!!
Part of the discrepancy may
Part of the discrepancy may have to do with Fukushima radiation plume flow patterns. Some areas of California will be more saturated, while other areas spared on the same given day. I have read that even within a few miles difference, radiation concentration levels can vary significantly. I was trying to track CPMs over time for a number of areas in California, and was struck by the fact that often San Francisco appeared to consistently come in at much lower CPM gross beta rates than did other areas of California, such as Los Angeles, Sacramento, Riverside...
In part, radiation plume flow may explain some of the differences. Unfortunately, we can no longer track these flow patterns. And, something else to consider. In part, radiation readings also appear to vary a great deal between geiger counter brands, and also vary according to how/where the geiger counters are installed to get the readings in the first place. Lots and lots of variable are present....
BRAWM, I, too, am interested in your take in the reading differences between the BRAWM and the Calif. Dept. of Public Health findings. Thanks!
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Can someone on the BRAWM team respond to this? I think they are valid questions and in the area of their expertise.
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