[ RadSafe ] FW: Reporter's question about lowerlimitsofdetection

[Busby, Chris]

When a car engine is running it works at varying rpm from 800 (tickover) to 3500 (revving).  If it is in a traffic jam and going slowly the engine is running slowly and taking in less air. When it is travelling fast, the engine is revving and taking more air.  The history of these cars is known and was reported by the owners. The mileage is on the odometer. I assumed 60km/h and 2500rpm as a mean. Actually this is quite a good method for estimating fuel consumption on a test rig and comparing it with average driving in town. So it is also a reliable estimate of the air flow, since the air mix is proportional to the fuel consumtion. In any case, the revs can only vary between 800 and 3500 rpm so that gives an outside limit. You can assume what you like. Do the sums and see what you get. You will always get a great deal more than the 2.7mBq/m3 from the global fallout or the 10mBq/m3 from Chernobyl in the N hemisphere.
You cannot calibrate an air filter with a vacuum cleaner. What do you mean? How would you measure the air that passed through it?
Chris  


-----Original Message-----
From: radsafe-bounces at agni.phys.iit.edu on behalf of Brennan, Mike  (DOH)
Sent: Mon 08/08/2011 17:03
To: The International Radiation Protection (Health Physics) MailingList
Subject: Re: [ RadSafe ] FW: Reporter's question about lowerlimitsofdetection
 
The number of km driven does not give you good information about how
much air was pulled through the filter, for the simple reason that
distance traveled in an uncontrolled environment does not correlate to
the amount of air that was pulled through the engine.  I have, over the
years, made a number of trips from my home to the nearest major airport,
about 45 miles away.  I have made the trip in as little as 45 minutes,
when traveling in the early morning when traffic was light.  I have also
made the trip in almost 2 hour during the middle of the day.  Same
distance, very different times, gas mileage, and amount of air through
the filter.  Additionally, the daytime trip probably had more
particulate in the air to act as sites for contamination (including
radioactive material) to attach to.  

Given that you could have used a vacuum cleaner with a filter over the
hose, and calibrated the flow with little trouble, I have to admit to
the suspicion that you chose the automobile filter specifically BECAUSE
of the unknowns, which you could manipulate to support your agenda.