[ RadSafe ] Swabbing the Bonnet (hood)

[Brennan, Mike (DOH)]

One of the most entertaining ways of calibrating a vacuum cleaner:

(1) set up intake with filter (such as paper napkin held over hose with
hose clamp, rubber bands, bungee cord, whatever)
(2) attach exhaust hose (usually you have to get if from some compatible
vacuum cleaner)
(3) make up a good bubble mixture of soap and water.  
(4) rig a stand for the exhaust hose that hold the end a known distance
from something sharp (actually, anything will do, but sharp looks more
dramatic)
(5) dip end of exhaust hose in bubble mixture, quickly clamp into rig
(6) turn on vacuum cleaner.  Time how long it takes for the bubble to
expand to the point and pop
(7) calculate volume of bubble, assuming it is a sphere (it's always
better if you can assume something is a sphere).  Using the volume and
time, calculate flow rate in whatever units trip your trigger.
(8) don't run the vacuum too long, or the napkin is likely to fail.

If you can't have fun with this set up, you are just doing SCIENCE!
wrong.  

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Rees, Brian G
Sent: Tuesday, August 09, 2011 3:22 PM
To: 'radsafe at health.phys.iit.edu'
Subject: Re: [ RadSafe ] Swabbing the Bonnet (hood)

Along that line, I've run a vacuum cleaner with a napkin on the nozzle
for demos with school kids to collect Rn progeny and to do a half-life
graphing exercise.  Just do a "calibration" just before the demo to
determine how long to run the vacuum that day.

Brian Rees

----- Original Message -----
From: radsafe-bounces at health.phys.iit.edu
<radsafe-bounces at health.phys.iit.edu>
To: The International Radiation Protection (Health Physics) MailingList
<radsafe at health.phys.iit.edu>
Sent: Tue Aug 09 14:26:21 2011
Subject: [ RadSafe ] Swabbing the Bonnet (hood)

Michael Cowie wrote:

>Why bother with the filters at all, you would have been better just
taking a swab of the bonnet (hood for the US contingent).......think
about that!

Hi, Michael.

Interesting you should write that, as I have sent some time thinking
with the idea of how to use cars for sampling in an event.

I like cars as a place to get deposition; certainly better than dirt or
vegetation.  If you pick the vehicle, you can have one that was blown
free of loose contamination prior to a known point in time (when it
parked).  The surface usually does not absorb contamination, so anything
that deposits is loose.  One of the things we've been playing with is
using a slightly sticky material as a collection medium.  I was
originally thinking post-it notes, but packing slip envelopes now seem a
better choice.  I personally like the windshield as a sampling site, as
it is less likely to ruin the paint job (and let's face it; if you are
seriously sampling for radioactive deposition, the owner of the vehicle
may already be stressed, and may not need much prompting to react
poorly).  

A while ago a member of the public who sends me things that fan his
fears about Fukushima (notice the alliteration?  Who says scientists
can't be poets) sent me a link to someone talking about wiping mist off
his windshield and counting with a radiation meter, and it was "hot"
(this was in California in late July).  I tried the same thing here in
Washington, and also found the mist on my windshield to be well above
background.  However, unlike the people claiming that there was material
from Fukushima still falling in the US, I did a decay study, and in 5
hours it had decayed to almost background.  I concluded that all to
almost all (note the inclusion of an uncertainty term, even in a
qualitative description) of the activity was due to radon decay
products.  

Anyway, I think that in the right circumstances useful information can
be had by using a car as a sampling site.   
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