[ RadSafe ] FW: Reporter's question about lower limits of detection

[stewart farber]

Hello all,

Firstly, it's important for Chris Busby to read what a person writes
carefully before criticizing it, and to keep in mind the concept of
comparing Apples vs. Oranges.

My remarks yesterday which Busby criticized, made in my comment to a
question from reporter Matt Wald of the NYTimes,  never mentioned the levels
of Cs-137 in air in Japan after the accident, rather the levels of airborne
radioactivity measured in the US following the accident. I made a general
comment, not a distorted point, about airborne levels of Sr-90 IN THE US
having been much higher in the 1960s than they have been IN THE US since the
accident in Japan.

My comment is completely irrefutable based on data derived from proper
sampling techniques used by the USEPA, and the US Environmental Measurements
Lab,  and analytical measurements performed using calibrated geometries in
counting airborne particulate samples gathered in the US after the accident
following the earthquake and tsunami which severely damaged the Fukushima
nuclear complex.

Busby provides a calculated value for airborne Cs-134 at several locations
in Japan based on his collecting and analyzing several auto air filters
while guessing at the volume of air sampled. The numbers he quotes for
airborne Cs in Japan are meaningless based on the major uncertainty of the
sampling technique employed, the uncertainly in many variables like filter
efficiency, and no details on how the auto air filter was configured for
counting in a calibrated geometry. In any case, I wasn't saying anything
about Cs airborne levels in Japan, so any data there no matter how gathered,
is simply irrelevant to my comment yesterday--- Apples.

Oranges:

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
Maximum: 0.116
Average: 0.0189

The above EPA data can be seen at:
<http://oaspub.epa.gov/enviro/erams_query_v2.simple_output?Llocation=EPA+Reg
ion&subloc=09&media=AIR-FILTER&radi=Cesium-137&Fromyear=2011&Toyear=2011&uni
ts=Traditional>


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
the US.

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
measured concentrations. 

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

Cheers as is often said.

Stewart Farber, MS Public Health
 
===========================================
-----Original Message-----
From: Busby, Chris [mailto:C.Busby at ulster.ac.uk] 
Sent: Friday, August 05, 2011 5:46 PM
To: safarber at optonline.net; The International Radiation Protection (Health
Physics) Mailing List; 

Dear Radsafers,
This is a reply to Stuart Farber who talks about trivial levels from
Fukushima. I have measured Cs137 in air filters from cars driving for known
periods of time 100km from Fukushima and in one case in Chiba which is East
of Tokyo. I have used NaiTl and also had the labs at Harwell do high
resolution counting.  Activity of Cs134 in these Filters was between 120 and
270Bq.
This can be shown (from the cubic capacity of the engine, the rpm and the
mileage after Fk) to give levels of Cs137 of about 1-3Bq/cubic metre.
Northerm hemisphere peak activity of Cs137 was about 2 to 3mBq
(milliBecquerels, Yes) Cs-137 per cubic metre as measured in Harwell UK at
the peak opf the fallout in 1963. I just say this to advise you that the
Fukushima releases are not trivial. About 1000 times higher than the peak
fallout levels.
Cheers
Chris

===================
Post excerpt [sent 05/08/11 18:57]
 by S. Farber to Radsafe to which Dr. Busby commented above

"During the days of open air testing of nuclear weapons by the US and
Soviets
[thru 1963] and after 1968 when most of this nuclear bomb released
radioactivity had left the stratosphere and come to deposit on the earth's
surface, Sr-90 and every other fallout radionuclide was much, MUCH higher
than levels one would measure today in almost all sample media. Levels of
Sr-90 in surface water, and air, and fish and other biota were much higher
than today. People [and the media] who have panicked recently from trivial
levels [in terms of radiation dose and risk] of measurable contamination in
the US from Fukushima, overlook the fact that during the days of open air
nuclear testing,  levels of radioactivity were hundreds to thousands of
times
higher in some cases. The amazing thing about measuring radiation is you can
measure a few atoms of some isotope decaying with accuracy and precision,
vs. the best chemical contaminant analytical technique requiring
countess[sic- should read countless] "billions and billions" of atoms as
Sagan so enjoyed saying.

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