[ RadSafe ] Field determination of radon progeny

[Brennan, Mike (DOH)]

Another situation in which a tizzy might develop is if you are collecting air particulate samples on a weekly, bi-weekly, etc. schedule, and you shift to daily because of an event.  Even if you wait 5 hours before counting (and depending on how exciting the event, policy makers might not want to wait), the activity per volume of air will be higher when the filters are changed daily, as opposed to a long period.  This is because the radon daughters collected early in the sampling period will be decaying for the entire time the sample is being collected.  Although we use the assumption that the daughters decay away in 5 hours, that isn't really true, and the longer a sample has to decay, the less activity will be on the filter.  

This is a good thing to make clear early, preferably before there is an event.  It saves on stress, latter.  

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu [mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Stewart Farber
Sent: Tuesday, April 13, 2010 12:38 PM
To: Mike (DNRE)McCarty
Cc: radsafe at agni.phys.iit.edu
Subject: Re: [ RadSafe ] Field determination of radon progeny

Hi Mike,
Regarding your question. There are many fine points about the behavior of radon, and background variations related to rainfall, snow cover, ground freeze, etc. Many of these are documented in the literature.

I should have written up the data on rainfall rate, radon daughter washout, and short term gamma exposure rate measurements in the case mentioned as a note to Health Physics at the time [the data was gathered in 1975 or so!!! ].  The data did document an interesting situation. Somewhere, buried in old files are graphs of the variation of background mentioned, plotted along with the rainfall rate. At the time I was acting as staff meteorologist for a central corporate nuclear services division, and also responsible for overseeing environmental rad monitoring at the nuclear plant in question. So continuously monitored rad exposure data measured with a HPIC at the site boundary,   and met data [including rainfall rate] for the same time
 period from a new met tower about 1000' [900 m] away were available, which allowed the relationship mentioned to be clearly seen.

Once used the info mentioned in my prior post  in an Emergency Planning training class to let folks know that you can get short term 75% increases [or perhaps more] in background at any distance from a facility that have nothing to do with a nuclear plant's operation. It is conceivable that such an observation would throw some into a tizzy if there was some report of a problem at the facility and suddenly someone, perhaps dozens of miles away, measured a 75% increase in exposure rate. As an aside, it is possible to infer if the increases in exposure rate at some location are due to airborne plant releases, since the standard deviation of 5 minute averages about the hourly mean generally exceeds a value that is not seen due to other causes.

Stewart Farber, MSPH

Farber Medical Solutions, LLC

Bridgeport, CT 06604



[203] 441-8433 [o]

website: http://www.farber-medical.com

======================