[ RadSafe ] FW: Reporter's question about lower limits ofdetection
C.Busby at ulster.ac.uk
Sun Aug 7 07:39:08 CDT 2011
It was my intention to show that the levels in Japan in air were not trivial. I do know this because I have measured it in several car filters for which the engine size is known and the number of km driven after the incident is known. The efficiency of the filters is assumed to be 50% but this is not known for sure although I have asked the manufacturers. The filters showed between 1.2 and 3Bq per cu metre of Cs-137. This can be compared with the attached data from Harwell. The results were from my lab and also from Harwell who we paid to do the analysis.
I am interested to learn that the levels were higher in the USA during the atmospheric tests than in the UK: Stewart Farber says 100mBq/m3. Probably because the US is where many of the tests were done.
But my argument was about Japan, not levels in the USA. I am quite aware that the levels in the USA were far smaller, as we would expect. But i see a maximum of 0.116pCi is 4.29mBq/m3 The average is 0.7mBq/m3. Compare with the graph attached. But I think it depends on where you live, doesnt it? And what other stuff comes along as a passenger.
The US EPA made excellent measurements of airborne Cs-137 in the US released
from Fukushima after the accident. Air particulate samples were taken all
over the USA by the EPA. Based on calibrated Hi-Vo samplers and calibrated
counting geometry for air filters, the highest levels of Cs-137 in air
measured were seen in HI, CA, AZ, NV. Cs-137 levels were reported as
[picoCuries per cubic meter]:
Minimum: 0.000238 pCi/m^3
The above EPA data can be seen at:
Open air testing of 500 nuclear bombs by the US and Soviets, ending in 1963,
led to many years of significant ongoing nuclear fallout from the mid 1950s,
reaching a peak level of total terrestrial deposition in 1968. After 1968
the environmental inventory of Cs-137 and Sr-90 continued to drop steadily
with minor blips in the US from small nuclear bomb tests by India and China.
Chernobyl added no more than 1% to the environmental fallout inventory in
During the MANY YEARS of nuclear test fallout airborne Cs-137 in essentially
the entire Northern Hemisphere, including the US, was roughly about 0.1
pCi/m^3. Peak levels of airborne Cs-137 during the period of open air
testing were commonly measured at 0.5 pCi/m^3 and higher.
As noted above, the EPA measured a SHORT TERM average of airborne Cs-137 in
the US from Fukushima of 0.0189 pCi/m^3 in those states having the highest
The LONG-TERM average level of airborne Cs-137 in the US during the many
years of atomic bomb fallout during and for a few years after open air
testing ended was about 5 times higher than the average SHORT TERM peak
levels of accurately sampled and measured airborne Cs-137 seen in the US
from Fukushima [based upon a few measurements fading away to essentially
nothing after a short time].
Given that what is important in calculating total radiation dose is the
ratio of the time integrated concentration of airborne exposure to Cs-137 in
this case, the total exposure of people in the US from open air testing
fallout is at least 500 times greater than the total exposure from
short-term peak airborne Cs-137 in the US measured after the Fukushima
accident [in looking at the areas in the US that had the highest recent
airborne Cs-137 levels].
And yes, I consider total time-integrated exposure to Fukushima airborne
Cs-137 and Sr-90 in the US that is about one part in 500 [or less] of the
time integrated radiation exposure from nuclear bomb test fallout in the US
to be trivial. -Oranges
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