[ RadSafe ] FW: ...detection (BUSBY)

radbloom at comcast.net radbloom at comcast.net
Tue Aug 9 18:42:50 CDT 2011



Your answer is interesting.  In this instance, it is not clear that 50% mass collection of air particulate would be the same as 50% radioactivity collection given that your additional research with the manufacturers of auto filters shows particles of less than 5 to 6 um AMAD (is this the right unit - this is activity median aerodynamic diameter and it seems unlikely that auto manufactures would use this unit [more likely they would care about mass median diameter]?) would not be collected at all.  I'm a little concerned about the reported efficiency with cut off range.  Does this mean some manufacturers report 96% efficiency for particles greater than 5 um AMAD (I'm using your unit, but think it might not be right) and some report the same efficiency for particles greater than 6 um AMAD?  I don't have your reference at this time, but I have to wonder if the atmospheric particles are measured at some great height or if they are measured at ground level.  Also, now that you've led me to think about that, I would guess that the cars would make their own dust clouds, and elevate any settled dust.  Also, I wonder how a speeding (or idling) car would perturb the particle sizes that would impinge upon the air filter.  I don't think you can conclude that if indeed 11% of the atmospheric particles are above 3.2 microns (would that be physical measurement, or some distribution, i.e., mass median diameter [MMD], AMAD, etc.?), that the air radioactivity would be larger, because you don't really have any studies indicating what particle size distribution from Fukishima was airborne during the collection period.  I don't see the origin of your factor of "4 to 5," and am pretty sure you can't really get there from here.  These do seem to be interesting qualitative measurements, but there are so many uncertainties in the many variables you need to quantitatively determine the concentrations, that I don't think you can get to a meaningful quantitative measurement.  Also quantitative measurements should include estimates of uncertainty (always an interesting exercise), and in this case, information regarding the radioactive particle distribution would also be needed. 


As I think about this a bit more, you stated previously that the filters were collected after 150 km of driving - that's about half the distance between Fukushima and Tokyo.  Where did the driving take place?  Was the driving in multiple areas, in a straight line or was it circling some location?  Would temperature, humidity, rain, etc. influence the cited filter collection efficiencies?  I'm not sure what one could to do with a number like this, the average air concentration over a distance of 150  km. 


Rambled and pondered enough, 


----- Original Message -----

From: "Chris Busby" <C.Busby at ulster.ac.uk> 
To: "The International Radiation Protection (Health Physics) Mailing List" <radsafe at agni.phys.iit.edu>, "The International Radiation Protection (Health Physics) Mailing List" <radsafe at agni.phys.iit.edu> 
Sent: Tuesday, August 9, 2011 1:30:06 PM 
Subject: Re: [ RadSafe ] FW: ...detection (BUSBY) 


I already answered this one . 

The activity on the filter is the activity on the filter, as you say. But we dont know how much of the particles in the air are trapped. So we can only use the activity in the filter as a indication of the activity in the air. I assumed 50% mass wiould stick in the filter. This was based on my reasearches on DU particles and filters. Actually now I have gone to the manufacturers and I do know.  The manufacturers tell me that they trap 96% of all particles above 5-6 microns AMAd and let the rest through. The particle size spectrum of atmospheric partciles over the land has been measured (Christian Junge, Atmospheric Radioactivity 1963 Table 28). Using this we can see that actually only 11% are above 3.2 microns. So that means we can calculate that there is more radioactivity in the air than I thought, by a factor of 4 to 5. 
Is that helpful? 

-----Original Message----- 
From: radsafe-bounces at agni.phys.iit.edu on behalf of radbloom at comcast.net 
Sent: Mon 08/08/2011 20:47 
To: The International Radiation Protection (Health Physics) Mailing List 
Subject: Re: [ RadSafe ] FW: ...detection (BUSBY) 



I'm confused.  How could the activity on the filter be larger if your assumptions change?  Isn't the activity on the filter simply what you measure, i.e., the activity on the filter? The calculations  (and assumptions) are all related to determining activity concentrations.  Granted the you could say that the there would have been more or less activity on the filter if collection efficiency, air flow, etc. changed, but all that is getting you back to concentration. 


I would also imagine the uncertainty in the  guestimated  air flow is pretty large and the other contributors' comments regarding particle size distributions, collection efficiency, etc., and driving scenarios (fast, slow, stop and go, idle time) add to the confounding of such calculations. 



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