Steven Dapra sjd at swcp.com
Tue Aug 9 20:03:19 CDT 2011

```Aug. 9

Let's all take a deep breath. . . .  Forget about filters,
their efficiency, miles driven, and all the rest of it.

Below, Chris Busby says, "The [car] filters showed between
1.2 and 3Bq per cu metre of Cs-137."  Right or wrong, let's stick with that.

Take such a filter and fasten it to the wall three feet
above the floor.  Ten feet from that filter, have reference man sit
in a chair facing the filter 24 h per d, for 365 d.  At the end of
the year, how much radiation exposure will reference man have
received from the 1.2 to 3Bq per cubic meter of Cs-137 that is in or
on the filter?

We need a specific figure, or at least a range within three
sigma.  I am assuming that it is possible to make such a
calculation.  If the answer is at or less than normal background (say
400 mrem), I would have to say that this entire argument about car
filters is a waste of time.

Can such a calculation be made?

Steven Dapra

At 06:39 AM 8/7/2011, you wrote:

>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.
>
>Cheers
>Chris

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